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The Magnetic Universe The Magnetic Universe
The Magnetic Universe

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

The Magnetic Universe

Lucie Green takes a closer look at how magnetic fields have shaped the cosmos.

The Sun's Magnetic Field

The Sun's magnetic field and the release of plasma directly affect Earth and the rest of the solar system. Solar wind shapes the Earth's magnetosphere and magnetic storms are illustrated here as approaching Earth. The white lines represent the solar wind; the purple line is the bow shock line; and the blue lines surrounding the Earth represent its protective magnetosphere. (Image and caption courtesy of NASA Image Gallery)

You can't see it, but it's there. All the time, and all around you. Protecting you from harmful space radiation and preventing our atmosphere from being stripped away by solar winds — it's the Earth's magnetic field.

For most of us, it hardly ever catches our attention. In observational astronomy, the Earth's magnetic poles are far less important than the geographic poles that we rely on to align our equatorially mounted telescopes. Consider this, though: the Earth's magnetic field probably made life on this planet possible, while more distant, cosmic magnetic fields are the reason that pulsars act like radio lighthouses and vast clouds of electrically conducting gas get sculpted into strange and unusual shapes.

As magnetic fields go, Earth's is the one we're most familiar with and its origin lies in the electric currents that flow in the molten iron that makes up our planet's outer core.

Planetary magnetism

Let's take a step back and look at Earth from the surface of the Moon. From here, we can see the land, oceans and atmosphere. What we can't see, however, is how the Earth's magnetic field envelops it all and extends out into space. For most of the time the Moon is inside the Earth's magnetic field. It only pops out for a few days around the time of new Moon. When it does, the Moon moves into the solar wind — the Sun's outer atmosphere that expands into space at a speed of a million miles an hour.

This wind can't penetrate Earth's magnetic field and instead slams straight into it. Although this interaction is invisible to the human eye, it does produce something spectacular: the aurora. As the solar wind pushes against Earth's magnetic field, it adds energy to it that accelerates charged particles down into our atmosphere. When the particles interact with atmospheric gas, they pass their energy on and cause the gas to glow.

The solar wind is blocked from reaching our atmosphere because it too contains a magnetic field. We've learned that any magnetic field that threads through an electrically charged gas (a plasma) is tied to that gas; they can't be easily separated, or decoupled, as the process is known. So when the gusty flow of magnetized plasma reaches the Earth's magnetic field, it flows around it, causing it to move and ripple like a windsock in a breeze. This property prevents the solar wind from reaching our atmosphere and stripping it away, as happened on Mars. It also provides us with protection from electrically charged cosmic rays.

This life-preserving property that planetary magnetic fields have means that it's important to consider them when it comes to studying exoplanets. So far, we're unable to directly observe an exoplanet's magnetic field. But should a technique for detecting them be developed in the future, the presence of a magnetic field around an exoplanet is likely to influence which ones become targets for further study.

The discovery of the Sun's magnetic field came in 1908 and was made by American astronomer George Ellery Hale. It's impossible to look for and study cosmic magnetic fields without the ability to detect them from a distance using electromagnetic radiation. In 1896, Dutch physicist Pieter Zeeman was carrying out experiments when he found that a strong magnetic field could affect the light given off by a "luminous vapor". The spectral lines emitted by the vapor were broadened or, in extreme cases, split into several components. In a paper published in 1897, Zeeman suggested that his discovery might be used to detect cosmic magnetic fields.

Indeed, it was this technique that was used by Hale to detect the magnetic field of sunspots. The Zeeman effect also polarizes the light in particular ways that can be used to understand the strength and direction of the distant magnetic field, allowing astronomers to probe distant magnetism by studying electromagnetic radiation.

In fact, the Sun allows us to investigate cosmic magnetism up close. Observations of the Sun provide a fantastic level of detail that really shows us how dynamic stellar magnetic fields can be. The Sun has an overall magnetic field that connects the north and south magnetic poles, which are close to the heliographic north and south poles, as they are on Earth.

Small-scale magnetism

But closer inspection of the solar atmosphere reveals arches of magnetic field connecting pairs of sunspots and twisted magnetic field structures known as flux ropes. These ropes are revealed because glowing, electrically charged gas traces them out, similar to the way iron filings sprinkled around a bar magnet align themselves to the field lines. If you watch the Sun over time you'll see that these magnetic structures are always changing and often erupt into the Solar System. The Sun's spatially resolved dynamic activity, powered by magnetism, gives us a glimpse of what other stars are also up to. And it's not just main sequence stars that have important magnetic fields.

Pulsars are a sub-set of neutron stars. Formed from the collapsed cores of high-mass stars that have undergone a supernova explosion, they spin extremely rapidly. As they spin, they flash out pulses of radio waves, as if they were cosmic lighthouses. Some of them flash many times a second. When Jocelyn Bell-Burnell discovered pulsars in 1967 they were viewed as curious objects and jokingly labelled LGM for Little Green Men. But the radio flashes can be understood if you combine a very rapidly spinning star with a strong magnetic field.

As a dying star collapses, its magnetic field is also drawn in with the material of the star itself, intensifying the field strength to a trillion times that of the Earth's. The presence of the field causes charged particles to gyrate around the magnetic field lines and when this happens, radio waves can be created. The radio signal will be concentrated at the north and south magnetic poles of the neutron star. The final ingredient in the making of a pulsar is to have an offset between the star's axis of rotation and the axis connecting the magnetic poles. This means that as the neutron star spins, the radio beam will sweep across space and our radio telescopes can detect it. In fact, neutron stars are record holders when it comes to magnetism: another sub-set of these stars harbor the strongest magnetic fields in the Universe, a thousand times stronger than that of the pulsars. These objects are rather unsurprisingly known as magnetars.

Galactic magnetism

The magnetic field of Earth and the magnetic field of the Sun, thanks to the solar wind, are not the only fields we find ourselves immersed in. Our Galaxy, the Milky Way, has a magnetic field too, albeit with a strength tens of thousands of times less than that of the Earth's. What the galactic field does have in common with the Earth, though, is that rotation is at the heart of its existence.

Magnetic fields in astrophysical objects are created by dynamos, a mechanism in which the rotation of an electrically conductive liquid (such as the molten iron in the core of a planet) is converted into magnetic energy. In this way, how fast an astronomical object spins is an important aspect of magnetic fields and dynamos.

In this context we can understand why Earth has a relatively strong field whereas Mars, once thought to be more Earth-like than it is today, doesn't. Inside Earth, the rotating molten shell means its dynamo is still acting. Mars, on the other hand, had a dynamo, but it ceased acting when the interior of this smaller planet cooled and solidified, leaving only a remnant of its magnetic field locked up in its rocks.

When it comes to timescales, stars and planets can take anything from hours to weeks to complete a single rotation. But these bodies have been around for so long that plenty of time has passed during their lifetimes to sustain and even evolve their magnetic fields. For example, the Sun rotates once every 27 days and has been around for 4.5 billion years. Assuming that the rotation rate has been constant during all of this time, the Sun could have spun over 60 billion times. This isn't the case when it comes to galaxies though. Take the Milky Way: our Galaxy rotates once every few hundred million years, which means there has only been time for it to make a few hundred rotations. So, while a dynamo is important for our Galaxy, there are other additional processes that are making an impact and which still need to be understood.

In 2017, a team led by scientists from the Max Planck Institute for Radio Astronomy in Germany published work showing that galaxy observations can be used to investigate magnetic fields when the Universe was much younger too. Their study of a galaxy that is nearly five billion lightyears away allows us to look back into the early Universe to study the history and evolution of magnetic fields, providing insight into a question that astronomers have long wanted to answer: how long have magnetic fields existed for?

Magnetic fields are magnificent and common across the cosmos. From planets and stars, to galaxies and beyond. Along with gravity, magnetism is responsible for shaping and controlling what we observe. So, next time you look up — no matter what you're looking at — remember the invisible force that is helping shape our Universe.


What are magnetic fields?

Magnetism is a force that is intimately related to electricity. Whenever an electric current flows there will be an associated magnetic field in the surrounding space, or more generally, the movement of any charged particle will produce a magnetic field. Try turning your kettle on and off and see if your smartphone's compass app can detect the magnetic field generated as the current runs through the cable.

These fields have a direction, which is why Earth has a north and a south pole. When two magnetic fields come close to each other, they will try to align, potentially causing the physical objects causing them to move — a compass needle has a magnetic field, and so will always try to line up with Earth's field and point north.

Similarly, the motion of a charged particle will change as it passes through a magnetized area, due to the interaction of the electric and magnetic fields. How the direction changes depends on the charge and mass of the particle, the strength and direction of magnetic field and how fast the particle is travelling.

ABOUT THE WRITER
Lucie is a Professor of Physics and a Royal Society University Research Fellow based at the Mullard Space Science Lab.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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Getting to the Heart of Pluto Getting to the Heart of Pluto
Getting to the Heart of Pluto

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Getting to the Heart of Pluto

Two years since the New Horizons flyby, Paul Abel reveals how its data is driving new discoveries about the dwarf planet.

Getting to the Heart of Pluto

Four images from New Horizons' Long Range Reconnaissance Imager (LORRI) were combined with color data from the Ralph instrument to create this global view of Pluto. (The lower right edge of Pluto in this view currently lacks high-resolution color coverage.) The images, taken when the spacecraft was 280,000 miles (450,000 kilometers) away, show features as small as 1.4 miles (2.2 kilometers), twice the resolution of the single-image view taken on July 13 [2015]. By NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research InstitutePublic Domain

On 14 July, it will be two years since New Horizons made its historic closest approach of dwarf planet Pluto. Nine years after its launch in 2006, the spacecraft became the first robotic emissary from Earth to survey this frozen enigma, which has spent much of humanity's existence lost in the frozen darkness of the outer Solar System.

Back in the summer of 2015 we looked at the history of Pluto and made some predictions about what New Horizons might reveal. Now we return to those predictions and look at the exciting discoveries that have been made about this fascinating sentry of the distant Kuiper Belt.

A patchwork surface

In the decades following its discovery Pluto remained little more than a speck of light, even when glimpsed by the world's largest telescopes. In 2002-03, the Hubble Space Telescope produced the first map of its surface, which provided tantalizing hints of a patchwork body. While there was speculation about the existence of cryovolcanism and stunning surface features in the 2015 feature, and some might have thought the author was — as Patrick might have said — letting his imagination run riot, after the flyby it seemed that more imagination was needed.

Dominating the surface of Pluto is the bright, heart-shaped feature known as the Tombaugh Regio, where New Horizons has discovered evidence of some spectacular geological activity. The western lobe is formed by the Sputnik Planitia, a vast, smooth deposit of bright carbon-monoxide ice. It is some 1,050x800km in size, making it the largest glacier in the Solar System. To the south we have the mountains Hillary and Norgay Montes. Norgay Montes is about 3.4km high and largely made of water-ice. There is evidence of ice flows here, and hints of structures that resemble frozen lakes. The views from the top of these mountains are likely to be quite spectacular.

High-resolution images of the Sputnik Planitia show it to be formed of polygon convection cells. It is thought that nitrogen and carbon-monoxide ice is warmed by heat welling up from inside the cells, and that this ice then flows down to lower levels. The small pits located in the ice could be the result of the sublimation of nitrogen-ice. There are no surface craters here, and this has led scientists to conclude that this part of Pluto's surface must be younger than 10 million years old. Clearly, Pluto is still geologically active.

Other areas of interest include ancient dark terrain like the whale-shaped Cthulhu Regio: its dark red coloration is due to the presence of complex hydrocarbons called tholins. The cratering of this part of the surface would suggest it to be a few billion years old, certainly much older than the Sputnik Planitia.

The New Horizons data provides two possible candidates for cryovolcanism: Wright Mons and Piccard Mons. These two features are the tallest objects on the surface of Pluto, reaching a height of 4km. A series of dark irregular patches on the equator form the Brass Knuckles region. The dark patches are separated by bright ice-covered mountains, which themselves contain deep canyons and valleys. It seems that there is no dull place on the surface of Pluto!

A lively atmosphere

It had long been thought that Pluto's atmosphere would be interesting. Due to its rather elliptical orbit, the general consensus was that the atmosphere would freeze to the surface as Pluto moved farther from the Sun. However, scientists now believe that Pluto may have an atmosphere for most, if not all, of its long year. Pluto has a substantial axial tilt of about 120°, so as it orbits the Sun one pole is kept in shadow while the other remains in direct sunlight. New Horizons has revealed that methane and nitrogen are distributed all over the surface. This means that there is probably enough ice to sublimate and keep the atmosphere from completely condensing on the surface.

This does not mean that the atmosphere is static: indeed it is far more dynamic than we thought. Over Pluto's long history, changes in the axial tilt mean there may have been times when the atmosphere was much more dense than it is now. It has been suggested that the atmosphere may even become dense enough to allow the existence of lakes of liquid nitrogen on Pluto.

After New Horizons made its closest approach, its Long Range Reconnaissance Imager began to observe the dwarf planet and it made a surprising discovery: surrounding Pluto was a notable atmospheric haze. Unexpectedly, this haze seemed to be composed of several different layers. It is thought to be due to the interaction of Pluto's atmosphere with sunlight. Although the Sun is weak from this far away, it is still sufficient to break up methane in the upper atmosphere, allowing more complex hydrocarbons to form. These slowly fall to colder, lower altitudes, forming the haze. The Sun's ultraviolet rays convert them into compounds called tholins, the compound responsible for the dark coloration on Pluto's surface. This is a general picture however; the exact details have yet to be determined. No doubt there is a complex interplay between the atmosphere and the surface, creating the dramatic topography we have seen. If anything, New Horizons has revealed the atmosphere of Pluto to be just as fascinating and complex as the planet it enshrouds.

Fellow travelers

Pluto does not wander alone in space: it is accompanied by five satellites, Charon, Nix, Kerberos, Hydra and Styx. Charon is around one-eighth the mass of Pluto, and as a result the pair are tidally locked, which means they always present the same face to each other as they move around the Sun. Unlike our own Moon, Charon does not rise and set over the surface of Pluto, it remains fixed in the black sky.

New Horizons surveyed Charon and the results once more challenged the expectations of planetary scientists. Instead of a dead, cratered world, the spacecraft found a surface every bit as exciting as Pluto's. Charon has a dark red northern polar cap, and this is probably material that has escaped from Pluto's atmosphere. Running along its equator is a vast canyon system nearly 1,600km in length. What could have caused this enormous fracture?

Names from science fiction are given to features here and the aptly named Vulcan Planum is, as Mr. Spock would say, fascinating. There is surprisingly little cratering on this plain, which indicates that some sort of resurfacing has taken place; the fingerprints of cryovolcanism in action. New Horizons was also able to image the other satellites, although Nix was the only other moon close enough to show interesting surface details. The spacecraft showed a red patch on the surface similar to the dark coloration found on Pluto and Charon.

The continuing mission

Although the Pluto flyby has long since passed, New Horizons is far from finished. The mission has already been a spectacular success and it has transformed an object that was once just a pinprick of light on a photographic plate into a complex and diverse world.

The discovery of mountains and apparent ice floes shows that even out here, in the frozen extremities of the Solar System, geological activity is quite common. Like the satellites of Jupiter and Saturn, Pluto and Charon remind us that we were wrong to write them off as dead, airless worlds.

No doubt in years to come the next generation of planetary scientists will use data from New Horizons to formulate new models of these distant wanderers. In the larger picture they will help to provide a better understanding of the early Solar System. I would imagine there will be many more surprises in store as the story of Pluto embarks on a new chapter.

LIFE ON PLUTO

The dwarf planet's subsurface oceans are a well of possibility.

It is currently believed that under the thick icy surface of Pluto there is a vast layer of water-ice. Beneath this lies the core of Pluto, containing radioactive elements that would release heat as they decay, thawing the water-ice above. Indeed, there may have been enough heating to have produced yet-undiscovered subsurface oceans on the dwarf planet.

Data from New Horizons indicates that Sputnik Planitia is probably an impact basin formed when a large object collided with the surface. As a result of the collision, water from this subsurface ocean could have welled up to produce the vast glacier we see today. One can't help wondering whether conditions in the subterranean oceans of Pluto were ever right for life to have got started.

ABOUT THE WRITER
Paul Abel is an astronomer at the University of Leicester. He co-hosts BBC Sky at Night's Virtual Planetarium every month.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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Catching the Milky Way's Monsters Catching the Milky Way's Monsters
Catching the Milky Way's Monsters

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Catching the Milky Way's Monsters

A revolution that began with colliding neutron stars is taking place in astronomy. Will Gater looks at how electromagnetic and gravitational wave observations are expanding our view of the cosmos.

Milky Way 'Nessie'

The "Nessie" infrared-dark cloud observed by the Spitzer Space Telescope. By NASA/JPL/SSC Public domain, via Wikimedia Commons

A brave trio of astronomers based at Harvard's Center for Astrophysics have been monster hunting in the Milky Way. Their first discovery was 'Nessie'; not a creature from the depths of a Scottish loch, but rather a long, dark filament slashed through our Galaxy's disc. The structure, made up of a long thread of relatively dense gas whose sinuous turns reflect those of the monster 'seen' in the classic photo, is hundreds of lightyears long.

When I first heard about it, I thought the existence of such a structure was just a curiosity, but this 'Nessie' is a complicated beast. Understanding how such a filament could have formed, and how it has resisted being ripped apart by the turbulent structure of the Galaxy's gas clouds, is not easy. A proper survey is needed and others have set out on this quest before. Six separate papers have tried to compile catalogues of giant filaments, using data from infrared and radio surveys within which dense clumps of gas stand out. Some inspected their data by eye while others used algorithms and machine learning to look for long filaments, so the first task for Catherine Zucker — the PhD student leading this monster hunt — was to bring these different datasets together in a useful way, using data from ESA's Herschel observatory to measure their properties.

The results of her and her team's hard work are fascinating. There are, it turns out, several types of monsters lurking in the Milky Way. While all share a habitat — closer to the center of the Galaxy than we are, and close to the middle of the disc — there are distinct differences. The most obvious bear similarities to how we imagine the Loch Ness Monster to look: they're long, thin filaments that, thanks to a significant fraction of dense gas, appear capable of forming massive stars (in some, three quarters of their gas is dense enough to be able to form stars). Such large and thin features are almost certainly the result of gravity working on a grand scale. What's more, these giant filaments may be very important, acting like bones to underpin the whole spiral structure of the Milky Way.

The second type, which have less dense gas and a more rounded appearance, may be squeezed versions of normal molecular clouds, which form the bulk of the Milky Way's star-formation regions. A comparison with recent simulations suggests that this idea is at least plausible, though more work — probably with more powerful computers — is needed. The third and final type sits between the previous two; these are as thin as the 'Nessie' filament but contain relatively little dense gas. They seem to be networks of molecular clouds, sorted into a regular pattern by gas collapsing in a particular way, specifically due to something called a 'sausage instability' (a wonderful technical term).

The three types of filaments seem to tell different stories about how gas collapses locally and how the large-scale structure of the Milky Way is put together. In corralling all of these beasts in the same place, Zucker and her team have done a great service to those who'll follow and continue our exploration of the Milky Way's wild places.

ABOUT THE WRITER
Chris Lintott is an astrophysicist and co-presenter of The Sky at Night on BBC TV. He is also the director of the Zooniverse project.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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Ripples, Radiation and Revelation Ripples, Radiation and Revelation
Ripples, Radiation and Revelation

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Ripples, Radiation and Revelation

A revolution that began with colliding neutron stars is taking place in astronomy. Will Gater looks at how electromagnetic and gravitational wave observations are expanding our view of the cosmos.

The Solar System

By ESO (https://www.eso.org/public/images/eso0917a/) [CC BY 4.0], via Wikimedia Commons

Every so often, a true moment of scientific insight comes along, a moment that has a profound impact on how we explore the Universe. One such moment came in 2015 with the first detection of gravitational waves — ripples in the fabric of space-time that propagate from moving celestial bodies and violent events such as the merging of two black holes or neutron stars.

But despite the astronomical possibilities gravitational waves grant us, it was another, more recent, observation that opened up a new field of space science. That new field is multi-messenger astronomy, in which the secrets of the Universe are revealed through detecting and observing not only electromagnetic radiation, but gravitational waves and other celestial phenomena too. And its story begins around lunchtime, in August last year.

At 12:41 UT on 17 August 2017, the Laser Interferometer Gravitational-wave Observatory (LIGO) detectors in Washington and Louisiana, USA, sensed a gravitational wave washing over their respective sites. What happened next would thrill researchers and set off a dramatic chain of events.

Mere seconds later, in space, NASA's Fermi Gamma-ray Space Telescope and ESA's International Gamma-Ray Astrophysics Lab (INTEGRAL) satellite both caught a burst of gamma rays emanating from somewhere in the southern celestial hemisphere. Could the two things be related?

"Less than a minute after the gamma-ray [burst] was picked up by the Fermi team, they notified everyone else that they'd seen something interesting and gave a rough sky map of the location," recalls Dr. Michalis Agathos, a LIGO-Virgo Collaboration researcher based at the University of Cambridge.

The scramble to correlate

As news of the gamma-ray burst started to reach astronomers around the world, the LIGO researchers were already analyzing the wave their detectors had sensed, which they'd now catalogued as GW170817. Like the Fermi and INTEGRAL teams, the LIGO researchers notified collaborators at astronomical organizations around the world with access to telescopes observing across practically the entire electromagnetic spectrum.

Astronomers and gravitational wave researchers have started to work together like this in recent years in the hope of observing electromagnetic radiation (be it visible light, radio waves, X-rays or gammarays) from the events that trigger gravitational waves and send them rippling across the cosmos. Such an observation of electromagnetic radiation had never been made alongside a gravitational wave before but now, with GW170817, the LIGO-Virgo team worked with great urgency to notify their colleagues who had spotted the Gamma-ray burst.

"We already knew that the Fermi team had circulated [news of the Gamma-rays] so everyone at LIGO worked hard to get [details of GW170817] out fast with as much accurate information as possible," says Agathos.

Using data from a third detector, Virgo in Italy, the researchers were able to narrow down the area of the sky that GW170817 had come from. "When we cross-checked our sky map with that of Fermi, which was relatively wide but still narrowed down the location to a few hundred square degrees, we noticed a significant overlap. That encouraged people to believe that this was something that may be picked up by other telescopes," says Agathos.

On the ground, the professional observatories in Chile slewed towards the area specified by the LIGOVirgo team, picking out a new pinprick of light in NGC 4993, a galaxy around 130 million lightyears away. Meanwhile in orbit, both the Hubble Space Telescope and NASA's Swift satellite spotted it too, while the Chandra X-ray Observatory would later detect X-rays streaming from the same location. One estimate from the European Southern Observatory suggests that around 70 observatories saw the glowing dot that had appeared in the distant galaxy. More significant than the large number of eyes on the new spot of light, however, is what the diversity of observations constituted.

For the very first time, researchers had caught both electromagnetic radiation and gravitational waves emanating from an astronomical phenomenon. And with the data they'd amassed, the science of multimessenger astronomy — of studying distant celestial objects by examining more than just the light they emit — took a vast leap forward.

As had long been hoped, decades of technological improvements had brought gravitational wave detection to the point where it could work in concert with all kinds of observatories to provide astronomers with a new way to scrutinize astrophysical processes. And nowhere was this better demonstrated than in the revelations that came from the analysis of the GW170817 event.

Looking beyond the wave

"The data that we see in [a] gravitational wave detection is in a waveform," says Agathos. "You can see it as a wave that evolves in a certain way and the structure of it gives you information about the source that generated it."

Analysis of the GW170817 gravitational wave suggested that the event which had produced it was a violent collision between two neutron stars that had been spiraling in towards each other. When the two stars finally collided, the force of the impact shuddered the fabric of space-time, sending the gravitational wave rippling across the cosmos. It also illuminated their host galaxy with a powerful blast of radiation — the light the world's telescopes picked up in August.

The identification of a neutron star binary system as the origin of GW170817 was important in itself. The initial flash that the Fermi telescope saw was a phenomenon known as a short gamma-ray burst. Short gamma-ray bursts had been observed many times prior to the GW170817 event and one of the theories that astronomers had put forward for what causes them was the merging of neutron stars.

With Fermi's observation of the short gamma-ray burst and a simultaneous detection of a gravitational wave produced by a collision of neutron stars, astronomers now had a key piece of evidence to support that theory.

The kilonova question

This revelation from the study of the GW170817 gravitational wave was the first triumph of multimessenger astronomy, but it wasn't the only one. The telescopes observing the electromagnetic radiation from the explosion caused by the two neutron stars colliding were able to capture spectra of the event. In doing so they were able to shed light on one of the great enigmas in astrophysics: where some of the heaviest elements in the Universe come from.

"Once you have the spectrum you can infer things about the [chemical] composition of the matter that you're observing," says Agathos. "The fact that we saw spectral lines of certain elements in this detection indicated that a big portion of elements, such as gold, platinum, uranium or other heavy elements, [are] actually produced in this type of process. This had been an open question for decades."

Those heavy elements were flung out by the explosion observed by the follow-up telescopes &mash; a powerful blast known as a 'kilonova', which astronomers had for many years suspected would occur when two neutron stars smash together. Kilonovae are fainter and release less material than supernovae, but as they dim rapidly they're much more tricky to catch.

"Sometimes you can see objects that have characteristics which would have looked like the theoretical models put forward for a kilonova," says Dr Kate Maguire, an expert in supernovae from Queen's University, Belfast. "But because they fade away very quickly from their brightness we never had good datasets."

Indeed, the multi-messenger nature of the GW170817 observations was crucial to positively identifying it as the kilonova predicted by models. "This is the first object that's conclusively a kilonova, because we have the gravitational wave detection of the two neutron stars merging," adds Maguire.

More messages

Astronomers hope to make more multi-messenger observations of kilonovae in order to get a better understanding of these events. But future multimessenger astronomy studies may also offer new insight into their more energetic cousins, supernovae, as well. And that's because there's another type of 'messenger' to pick up, a messenger that wasn't detected in the GW170817 event but one that could reveal the inner workings of these violent stellar detonations: neutrinos.

Neutrino particles can be produced in the powerful core-collapse supernovae that occur when a massive star dies, but they're extraordinarily hard to detect and require specialist detectors, such as the IceCube Neutrino observatory located at the South Pole. "We've only seen neutrinos from one supernova, 1987A, and that was 20 neutrinos out nos [a theorized total of] 1058," says Maguire.

Nevertheless if a supernova went off in the Milky Way and enough neutrinos could be detected from the blast, along with gravitational waves and electromagnetic radiation, it would be a pivotal observation. "The neutrinos would tell us about the explosion mechanism of the core-collapse supernova," explains Maguire. "The gravitational wave detection would be very nice for tying down the properties of the system, such as the mass. And we'd have the electromagnetic radiation as well — because it would be a supernova in our galaxy we'd be able to get very detailed observations. It would be incredibly exciting if we were able to do that."

With LIGO coming back online later this year, professional astronomers will be preparing to jump into action when another gravitational wave signal is detected. But there's another development on the horizon that should excite amateur astronomers too. In the future, the private notifications that the LIGO team send out to collaborators alerting them to a potential new gravitational wave event will be made more widely available.

"One cannot exclude the possibility that certain sources may be observable by amateur astronomers with decent telescopes," says Agathos. "For instance the host galaxy of the first neutron star binary [merger] detection was something in the region of [mag.] +12.4 and the source itself was not much dimmer. With a decent telescope, if you're lucky enough and you're in a place where the sky is dark and clear, you may actually be able to discover things before the large telescopes do."

The future of multi-messenger astronomy will certainly involve advanced, professional observatories and rapid-reaction, wide-field telescopes working alongside gravitational wave and neutrino detectors. But in among the authors of forthcoming studies they produce, we may well also see the names of dedicated amateurs working from their own back gardens.

ABOUT THE WRITER
Will Gater is an astronomy journalist, author and presenter. Follow him on Twitter at @willgater or visit willgater.com.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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Spying on the Neighbors Spying on the Neighbors
Spying on the Neighbors

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Spying on the Neighbors

Hubble's successor, the James Webb Space Telescope, will look farther back in time and space than ever before. But this giant telescope could also be turned to targets right in our own cosmic backyard, as Benjamin Skuse reveals.

The Solar System

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Bigger and more powerful than any space observatory ever launched, the James Webb Space Telescope's (JSWT's) infrared gaze will stretch to the very first stars and galaxies being born, offering new insight into the Universe's origins. Its eyes will also scan exoplanets in the search for the building blocks of life beyond our cosmic doorstep, looking for answers to the perennial question: 'Are we alone?'

What many do not realize though is that JWST will not solely be peering at the farthest reaches of the Universe. In fact, with some clever reconfiguring, Webb will be able to cast its spying eye on our closest cosmic neighbors, hoping to uncover some of the secrets hidden within our Solar System.

Adapting JWST for the local nature of Solar System science, however, is fraught with difficulties. The biggest is that the telescope is designed for detecting the faintest, most distant objects. Its extremely sensitive sensors therefore need to be protected at all times from the overpowering light and heat from the Sun, which is why it is equipped with a tennis court-sized sunshield. This would not be a problem but for the fact that Webb will be located at the second Lagrangian point (L2), some 1.5 million km beyond Earth's orbit. As it is, the sunshield permanently shrouds Mercury, Venus, Earth and the Moon from Webb's gaze.

The closest of our neighbors Webb will be able to track are near-Earth objects (NEOs) like Eros and Halley's Comet. "The Earth's atmosphere makes it very difficult to observe NEOs in certain wavelength regions, some of which are very informative and diagnostic of things like water and organics," says NASA research scientist Cristina Thomas. "If we want to focus on origins of life questions, then going outside the atmosphere helps us."

The brightness dilemma

The second nearest target, Mars and its moons, will only be within JWST's spyglass every two years. Webb will add an infrared view to the Mars toolbox of rovers and satellites tasked with studying the planet and its potential for hosting life.

NASA planetary scientist Geronimo Villanueva believes this capability will be invaluable: "JWST will open a new window into the planet's current and past habitability," he says. Villanueva should know. Among other achievements, he was the co-discoverer of methane on the planet (a possible biosignature) and mapped deuterium to hydrogen ratios in Mars's atmospheric water — leading to the realization that the Red Planet had an ancient ocean. "New observations are urgently needed to confirm these findings," he says.

The Red Planet brings us to the second main challenge in using Webb to look over the garden fence: overexposure. Essentially, Mars is far too bright for the Webb's sensitive detectors to cope with. "Even Pluto is bright enough that if we took full-frame data with our widest filters it would saturate," says John Stansberry, a Space Telescope Science Institute (STScI) scientist. "So bright has a different definition for JWST!"

To get round this, NASA will command the instrument to just process a tiny square right in the middle of the full detector array. "Instead of having a 4-megapixel image, we'll take a much smaller postage stamp in the middle," says NASA space scientist Conor Nixon. "That way we can read that out really quickly before it becomes overexposed."

Beyond Mars is where JWST will really have to start getting busy. With an observing window of around 50 days approximately every six months, the giant planets Jupiter, Saturn, Uranus and Neptune will all be viewable, as well as their associated rings and 170 known moons.

While the planets themselves will be monitored by JWST, some of the most interesting science will concern their satellites. From helping to solve the tidal heating conundrum on Jupiter's moon Io to taking over the task of watching the Saturnian moon Titan after the Cassini mission comes to an end or even establishing whether Neptune's retrograde-orbit moon Triton has a subsurface ocean, JWST offers the chance to view and try to understand the most dynamic processes of the Solar System's satellites.

Focus on the small things

However, the bread and butter for JWST's Solar System science will be even less studied, smaller and distant bodies: comets, the main belt asteroids situated between Mars and Jupiter, the Trojan asteroids that share Jupiter's orbit, and the Kuiper Belt objects — including dwarf planet Pluto and the yet-to-be-seen Planet Nine. All could yield clues to how the Solar System came to be the home we know.

"Because they retain material from the very start of Solar System history, they reveal the chemical makeup of the planets and how planets form," says Andy Rivkin, planetary astronomer from Johns Hopkins University.

For these smaller distant bodies and ring systems, NASA has another trick up its sleeve: stellar occultations, where a star is temporarily blocked by a passing Solar System body.

"If you can take data very quickly as an object passes in front of a star, you can measure various things about the object itself," explains Stansberry. By looking at the changes to the star's light as it disappears behind a planet, Webb will be able to look at ring microstructures, and may discover rings around minor planets or even find atmospheres around various Kuiper Belt objects.

All of these proposed targets for Webb suggest the Solar System's most well-hidden mysteries may soon be solved, but one paper really sticks out as having the potential to captivate the public's imagination. In it, the authors propose using JWST and Hubble together to create stereo 3D movies of the planets and moons amateur astronomers have been fascinated by for centuries.

"I worked with a vision scientist colleague to understand the limits of human depth perception," says Joel Green, a project scientist at STScI, who led the study. "It turned out that if you had eyes one million miles apart, and the resolution of Hubble and Webb (roughly 1,000 times better than 20/20 vision), you could actually see objects like Mars, or Jupiter's moon system or Saturn's rings in stereo 3D!"

Not only might this be a boon to astronomers, offering stereo data on weather changes, collisional studies, ring system shocks, and many more, but would also be a first for science education, making ancient astronomical bodies come to life in the classroom. As Green notes: "These are the sorts of images that could inspire a generation."

ABOUT THE WRITER
Dr. Benjamin Skuse is a mathematician turned science writer based in Bristol, UK.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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Grand Designs Grand Designs
Grand Designs

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Grand Designs

Grand Canyon National Park is set to get a whole lot darker as it embraces its International Dark Sky status, writes Jamie Carter.

The Milky Way

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For anyone after an uplifting experience from nature, the Grand Canyon almost has it all. By day you can stand anywhere along its South Rim and peer down nearly 2,000m into its layer-cake bands of red rock, taking you back two billion years into Earth's deepest history. When the Sun goes down, the combination of a high elevation and dry desert air means clear, cloudless night skies are common. So why doesn't the Grand Canyon National Park have a particularly high reputation among amateur astronomers and astrophotographers?

Five million visitors per year, that's why. Most of them visit Grand Canyon Village on the South Rim, which is easily accessible from Flagstaff in Arizona and only a few hours from Las Vegas in neighboring Nevada. Over the years the undeniably picturesque properties on the South Rim added lighting. And then more lighting. Even the pathways along the rim were floodlit.

This wilderness gateway is now a major light polluter, but that's all set to change in the wake of the June 2016 announcement that the reserve has been provisionally designated as an International Dark Sky Park. This certification is awarded by the International Dark-Sky Association (IDA), a US-based organization that encourages others to maintain the darkness of the night sky for future generations.

The 'provisional' status reflects the complex job ahead. There are thousands of light fixtures on both rims and within the canyon itself, and the National Park Service has set a deadline of June 2019 — the park's centenary year — to retrofit two-thirds of them to comply with the IDA's lighting guidelines.

Harking back to darker times

"Technology is coming along nicely, with excellent night sky and eye-friendly choices now on the market, with prices that are becoming competitive with more common fixtures and bulbs," says Jane Rodgers, deputy chief science and resource management at Grand Canyon National Park, who applied for the Dark Sky Park status. "Backpackers and campers within the canyon will look up at the South Rim and see fewer, more subdued lights, most of which are illuminated only for a few hours after sunset and an hour or so before sunrise. The general aesthetics will hark back to the time when the village was first developed, where the natural world dominated and visitors experienced the feel of an amazing night sky."

Not that the national park doesn't already promote itself as a dark-sky destination. Its rangers are well informed about the night sky, and a star party has been held here each June for over a quarter of a century. Last year's even included talks in the visitor center, constellation tours and free telescope viewing outside the building and at nearby Mather Point, a 10-minute walk away on the rim.

The north-south divide

At other times of year (May to September pretty much guarantees a dry climate and crystal clear night skies), there are night-time walks and talks by rangers, who often set up a telescope for public use. Amateurs and professional astronomers from nearby Lowell Observatory in Flagstaff (where Clyde Tombaugh discovered Pluto) make visits, while on the darker North Rim, the Saguaro Astronomy Club of Phoenix set up telescopes on the porch of the Grand Canyon Lodge.

Mather Point is the best place for stargazing on the South Rim, though Rodgers is looking into establishing a designated night-sky viewing area. Nearby Hermit's Rest and the many pullouts on the flat Rim Trail are perfect, as are the remoter Desert View and Lipan Point on the South Rim, about 30km drive from Grand Canyon Village.

Alternatively, pitch a tent in one of the reserve's campgrounds. Here you may well find a ranger who can point out the local Navajo tribe's giant constellations: the First Revolving Male, First Revolving Female and the Central Fire. You'll recognize them; they're based on the Plough, Cassiopeia and Polaris, respectively. The constantly turning circumpolar stars represent the Navajo ideal home of a husband, a wife and an abode. By protecting natural darkness as well as the natural landscapes, Grand Canyon is itself committing to a beautiful billion-year marriage all of its own.

ABOUT THE WRITER
Eclipse-chaser and dark skies expert Jamie Carter is the author of A Stargazing Program for Beginners: A Pocket Field Guide

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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Capturing the Hunter Capturing the Hunter
Capturing the Hunter

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Capturing the Hunter

The familiar winter constellation of Orion holds many surprises for imagers who want to delve a little deeper, says Will Gater.

Orion Nebula

Photo taken by astrophotographer Steve Peters at Fremont Peak, California.

There are few constellations that grab the attention quite like that icon of the winter heavens, Orion. The glittering bright stars, the instantly recognizable 'belt' and the many glowing nebulae scattered within the Hunter's boundaries all make Orion a wonder to behold on a frosty, dark night. But the constellation is also a rich hunting ground for astrophotographers seeking captivating targets of many kinds. In this article we're going to explore some of the different ways Orion's splendors can be captured on camera, from a simple nightscape that conveys the naked-eye view to advanced CCD imaging techniques that can reveal the constellation's extraordinary deep-sky features. And hopefully, by the end of this piece, you'll agree with us that no matter how many times you catch sight of the Hunter, you'll always find something new to inspire you and test your astrophotography skills.

The Hunter in his element

Experience Level: Beginner to Intermediate
What You'll Need: A DSLR or bridge camera and a sturdy photographic tripod. A wide kit lens (of the kind that comes with most DSLRs) will be perfectly sufficient. More experienced astrophotographers may also want to use a portable tracking mount to capture longer exposures.

There's something tremendously evocative about glimpsing the bright stars of Orion over a wintery landscape — or towards the end of the autumn months just as the nights start to get longer and colder — so in this project we're going to look at how to shoot a 'nightscape' that attempts to capture some of that magic.

STEP 1: Make a conceptual plan
Thinking about the emotions you want to convey or elicit with your shot can help you to plan a powerful picture, and it'll inform every stage of the photographic process. For example, if you wanted to evoke the harsh iciness of winter observing you might shoot Orion over an isolated, leafless tree in a barren landscape, and process in such a way as to create a hard contrast between land and sky.

STEP 2: Select your focal length or a prime lens
Once you've thought about what atmosphere you want to capture with your image, you can select the focal length you'll be shooting at. A typical kit lens set to around 24mm, or an equivalent prime lens, provides a wide field of view for Orion on a camera's sensor, allowing you to fit in the brighter central stars and the Hunter's fainter outlying 'arms'.

STEP 3: Focus the view
Next focus the view. Some cameras have a live preview function that can be zoomed onto a suitable star, giving you instant feedback as you make slight focusing adjustments. With Orion there's no shortage of bright stars that can be used for this. Repeat the process a few times — checking that the star is a small as possible — so you're certain the image is as sharp as it can be.

STEP 4: Compose with the landscape and sky conditions
To compose your nightscape you can take short, very high ISO test exposures to show you the balance and positioning of foreground and sky, and any structures or landscape features in frame. Try to use the foreground — trees, buildings, etc. — to lead the viewer's eye toward Orion. Sometimes clouds can be used as a framing device too, and thin cloud can even 'bloat' and enhance the colors of bright stars.

STEP 5: Set the exposure length, aperture and ISO
When shooting, keep the lens aperture wide open (lowest f-stop), though some lenses will perform better when reduced a few stops. Experiment with the ISO and exposure length until you're happy with the look. You may need to use an exposure that very slightly trails the stars in order to define the foreground.

STEP 6: Process your image
When processing nightscapes, reducing the noise in the image and bringing out foreground detail are the main challenges; as long as you shoot in RAW format, modern image-processing software is well-equipped to handle these tasks. In Photoshop or GIMP you can correct the color balance, and use the 'Curves' tool to bring out star fields and improve overall contrast and definition.

Far and Wide

Reveal the hidden delights lurking within Orion with the help of long-exposure, wide-field imaging.

Experience Level: Intermediate
What You'll Need: A DSLR, a tracking mount and either a relatively long focal length camera lens (between 100 and 300mm focal length on a full-format DSLR) or a short focal length refractor. You could use a CCD camera, but the field of view produced by your setup will need to be at least 5° across or you'll need to mosaic.

One of the things that makes Orion so attractive for astrophotography is the diversity of deep-sky objects within its borders, from pinkish-red star forming regions to blue-tinted reflection nebulae.

The proximity of these targets to one another means that long-exposure wide-field imaging of Orion can produce some spectacular compositions. Not only do such wide-field images show the positions of objects such as the Orion and Horsehead Nebulae in relation to one another, but they can also reveal the rarely seen fainter surroundings of objects that are usually given the 'close-up' treatment, such as the aforementioned nebulae.

A DSLR with a long focal length lens and mounted on some form of equatorial tracking mount is probably the simplest setup with which to get started in wide-field imaging. Unlike most deep-sky imaging, wide-field deep-sky astrophotography generally doesn't require auto guiding, as it's possible to capture good data with unguided sub-exposures of just a minute or two.

With fast prime lenses and those relatively short exposure lengths, you may be surprised at how easily you can pick up some of Orion's most recognizable deep sky objects. For the best results capture multiple sub-exposures (as well as dark frames and flat fields) and then calibrate and stack them, using software such as the free DeepSkyStacker, before final enhancements in your preferred image processing software.

Colorful captures

With the right setup you can show Orion is more than just white stars against a black background.

Experience Level: Beginner

What You'll Need: A basic DSLR or bridge camera fitted with a lens that allows manual focusing (some compact digital cameras will also work depending on the lens/focusing mechanism they use). You'll also need a photographic tripod and your camera will need to be able to take exposures of a few seconds.

The color variation of Orion's bright stars is one of the most captivating things about the constellation, yet it can be tricky to capture these wonderful hues as the chromatic aberration in some camera lenses overwhelms the true star color. One method for showing the tints of stars such as Betelgeuse, Rigel and W Orionis is to manually defocus the image. It's a technique that was made famous by the renowned astrophotographer David Malin many years ago. You can use this method with a wide lens (or a fast long lens) on a static tripod, as long as you use short exposures — a second or so in the case of a longer lens. All you do is frame the star (or constellation), defocus the lens a little by hand and capture an exposure, usually at a mid-to-high level ISO setting. In the two composite images below we focused on Betelgeuse and Rigel. We captured a number of exposures and in between each one we defocused the lens a bit more. Then we combined them into one frame using processing software. It's a very artificial composition, but it does give a flavor of one of the things that makes observing and imaging Orion special.

Portrait of a stellar nursery

Capture the Orion Nebula's ethereal pink swirls of gas and dust that are giving birth to new stars.

Experience Level: Intermediate to advanced
What You'll Need: A small refractor or Newtonian telescope carried on a motorized tracking mount, plus a monochrome CCD camera (and a computer to control it) with a set of LRGB imaging filters and a filter wheel. For exposures of more than a few minutes it's also a good idea to use an autoguiding system alongside the above, though this is not absolutely necessary.

There are few greater tests of a deep-sky astrophotographer's skills than the magnificent Orion Nebula, M42. Among the many challenges it provides are the faint outer regions of the nebula that can be lost in processing, or simply not picked up at all during the imaging process, and its dazzlingly bright core that requires careful planning to capture. In the step-by-step guide below we've described the basic process of how to go about shooting M42 with the kind of setup you might typically have if you're starting out in CCD imaging — that is a monochrome CCD camera and a set of LRGB filters (luminance, red, green and blue) with which to make a full-color image.

STEP 1: Set up and polar align accurately
Once you've got your equipment set up, spend some time finessing the polar alignment of your mount. This is so you'll be able to get the longest unguided exposures your mount is capable of before the stars drift out of position — this is especially important if you're not using autoguiding equipment.

STEP 2: Capture different length luminance exposures
Use short, 'binned', test exposures to compose the image. Then take three groups of exposures through a clear luminance filter: short ones for M42's bright core, longer ones for the main body and, for the faint outer regions, as long as your unguided mount can manage without the stars 'wandering' (usually several minutes).

STEP 3: Get the RGB color
When you've got around 10-15 sub-exposures for each of the three groups of luminance data, you can move on to capturing the color data through red, green and blue filters. Capture at least 10-15 images per color channel — aim for an exposure length similar to your shots of the main body of M42 with the luminance filter.

STEP 4: Take dark frames and flat fields
After capturing each 'LRGB' channel, carefully stretch a clean white pillowcase or t-shirt over the scope aperture (without touching the lens) and illuminate it with a torch before taking an image. This is a flat field, which records image artefacts such as vignetting and dust on the optics. Also take a set of dark frames if the data from your CCD needs them.

STEP 5: Stack and calibrate the data
You should now have six sets of sub-exposures: three luminance groups of varying exposure length and one for each of the RGB channels. Load them into your preferred astronomical image processing software (for example, DeepSkyStacker) and use the flat fields and dark frames to calibrate them before stacking those calibrated sets into six images.

STEP 6: Combine the three luminance images
Bring the three luminance images into layers-based image processing software, such as Photoshop or GIMP. With each image in a separate layer, erase the overexposed portion of the long-exposure image so that the 'main-body' exposure shows through — do the same for the main body layer so the core shows clearly. Merge the layers.

STEP 7: Add the color and make final processing adjustments
Next, place your red, green and blue filtered images in their respective color 'channel' in a new image file. Copy the resulting full-color image, as a separate layer, into the luminance file created in Step 6 and turn its blending mode to 'Color'. Lastly make any final image tweaks to your taste.

ABOUT THE WRITER
Will Gater is an astronomy journalist, author and presenter. Follow him on Twitter at @willgater or visit willgater.com.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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Mission to Mercury Mission to Mercury
Mission to Mercury

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Mission to Mercury

October will see the launch of a European mission to the innermost world in our Solar System.

Mercury

By NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington [Public domain], via Wikimedia Commons

"A peculiar planet of mysteries and surprises" — this is how European planetary scientist Johannes Benkhoff describes Mercury. In October this year, ESA will launch the BepiColombo spacecraft to the Solar System's smallest and innermost planet. Some eight years from now, it will begin studying Mercury in meticulous detail across the electromagnetic spectrum. According to Benkhoff, the mission's project scientist, planetary researchers expect BepiColombo to solve many Mercurial mysteries. It's a planet, he says, that is also a key element in understanding the formation of the Solar System.

The mission's Ariane 5 rocket launch from French Guiana will send two orbiters to the planet: the relatively small Japanese Mercury Magnetospheric Orbiter (MMO) and ESA's 4,100kg Mercury Planetary Orbiter (MPO). Both are mounted on a six-meter tall transfer module that will deliver the two craft into orbit around the 4,879km-diameter planet.

"It's a very harsh environment," says Benkhoff, referring to Mercury's distance from the Sun, which varies between just 46 and 69 million km. "But if we're lucky, the nominal mission duration of one year may be extended up to four years."

Although Mercury is much closer to Earth than, say, Saturn, it's tough to get there, basically because the planet's orbital speed is much higher than Earth's. The first Mercury probe, NASA's Mariner 10, didn't even make it into orbit. Launched in 1973, it performed three close flybys in 1974 and 1975, before ending up orbiting the Sun. Mariner 10 mapped just shy of half of the planet's surface, revealing a crater pocked landscape. It also discovered a weak magnetic field: quite a surprise, since no one expects Mercury to have retained a molten core.

It would be 30 years before another probe set course for Mercury. NASA's MESSENGER spacecraft launched in August 2004, and orbited the barren world between March 2011 and its intentional crash in April 2015. From its polar orbit, MESSENGER collected nearly 290,000 images and mapped the planet's topography. Among other things, it discovered deposits of ice at the floors of permanently shadowed polar craters, mysterious 'hollows' beneath the surface, signs of relatively recent volcanic activity, and a mysterious displacement of the magnetic field by 400km northwards with respect to the planet's center.

So what's left for BepiColombo to discover? A lot, says former project manager Jan van Casteren at the European Space Research and Technology Center (ESTEC) in Noordwijk, the Netherlands. Originally, he says, BepiColombo was scheduled to arrive first, but the project was delayed by technological problems, cost overruns and redesigns. "Still, in 2009, ESA's Science Programme Committee decided to give the go-ahead for the mission because of its great scientific potential. BepiColombo is a much more versatile mission than MESSENGER, which was relatively simple."

No easy journey

During its seven-year cruise phase, BepiColombo's solar orbit will gradually be tweaked by one Earth flyby, two Venus flybys and no less than six Mercury flybys. This 'gravity assist' technique, pioneered by Mariner 10, was invented by Italian astronomer Giuseppi 'Bepi' Colombo, after whom the mission is named. The craft's versatile ion engine will perform additional orbital corrections. Eventually, in early December 2025, BepiColombo will arrive in its elliptical polar orbit. A few months later, the lowest point of the orbit is brought down to just 250km, and science operations will begin.

At Mercury, a spacecraft receives about 10 times more solar energy than it would in Earth orbit: some 14,500 watts per square meter. Moreover, Mercury's surface is so hot (430°C) that BepiColombo's main orbiter needs to be protected from the planet's infrared radiation, which delivers more energy: 5,500 watts per square meter. To cope with these extremes, the craft is completely wrapped in thick, multilayer thermal blankets. A huge contraption of silver-coated titanium fins always points away from the planet to radiate excess heat away into space.

You might expect that the use of solar panels is straightforward when you're so close to the Sun, but you'd be wrong, as Markus Schelkle of Airbus Defence and Space in Germany (the spacecraft's prime contractor) explains. "The solar array had to be newly developed using novel materials," he says. "It's very difficult to make them resistant to both high temperatures and strong ultraviolet radiation." The same is true for the large solar arrays on BepiColombo's transfer module, which provide the energy for the ion engine. "Developing the solar arrays took as long as developing the whole spacecraft," says Schelkle.

As the MPO studies the planet up close, the smaller MMO will monitor the solar wind, the planet's magnetic field and the extremely tenuous sodium-rich 'exosphere'. Because of strong solar wind buffeting, Mercury's magnetosphere can sometimes be pushed back all the way to the surface. As a result, the solar wind directly interacts with the surface, possibly releasing sodium atoms in the process. "It's one of the questions we want to answer," says Hajime Hayakawa of the Japanese space agency JAXA. Another big issue he hopes MMO will solve is the mysterious 'shift' of Mercury's magnetic dipole. Meanwhile, as project scientist Benkhoff recounts, the MPO will map the elemental and chemical composition of the planet's surface, look for morphological changes in the mysterious subsurface 'hollows' (which may be due to the loss of volatiles), hopefully elucidate the origin of the polar ice deposits and study the planet's relatively large iron-nickel core. "Also," says Benkhoff, "Mercury's potassium/thorium ratio is much higher than current planetary formation models predict. The mission may shed new light on the origin of the Solar System." Van Casteren is confident that the ambitious €1.65 billion mission will be worth every penny. "The highest resolution images will reveal details as small as 5m," he says, "and BepiColombo has an impressive suite of 11 science experiments. It would have been nice to be the first, but in the long run, it's the science that counts."


TARGET MERCURY

Why is studying Mercury so tricky, and what might we learn from doing so?

Mercury is the smallest and innermost planet in the Solar System. Studying it from Earth (or with an Earth-orbiting instrument like the Hubble Space Telescope) is difficult, because it always appears close to the Sun in the sky.

Because Mercury is orbiting the Sun so fast (48kms on average), a spacecraft launched from Earth has to undergo a large change in velocity to end up orbiting the planet. That's one reason why there have been so few Mercury probes so far.

Visible light, X-rays and ultraviolet radiation from the Sun are about 10 times more powerful at Mercury than they are on Earth. The solar wind (charged particles from the Sun) is also more energetic. This is another reason why Mercury has remained relatively unexplored.

Compared to the other terrestrial planets, Mercury has a very large iron-nickel core. No one knows why. Maybe a huge primordial impact blew away most of its rocky mantle. Or maybe scientists need to adapt their pet theories on the formation of the Solar System.

Learning more about Mercury and its extreme environment will also help in understanding habitable-zone exoplanets that orbit at comparable distances to their parent dwarf stars.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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The Three Types of Twilight The Three Types of Twilight
The Three Types of Twilight

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

The Three Types of Twilight

The period between 'day' and 'night' is complex, and so is the sky at this time.

earth

By Pmurph5 (Own work) [CC BY-SA 4.0], via Wikimedia Commons

The changes that occur during dusk can be as striking as anything we observe in nature. Everything we can see changes, as the brightness of the sky drops to less than 3/10,000ths of a per cent of its intensity at sunset. Yet this daily spectacle is often lost to us, perhaps obscured by cloud, but also obliterated by artificial lighting and sometimes simply ignored because of its regularity.

Twilight is not a single, fixed state, but a gradual change that has three distinct phases. The first is civil twilight, which begins as the upper limb of the Sun disappears below the horizon and ends at civil dusk, when the geometric center of the Sun is 6° below the horizon. During this period, you can carry on doing things much the same as if the Sun were above the horizon, lit only by the still-blue overhead sky. The first half an hour being dubbed by photographers as the 'blue hour'.

We tend to look to the west at sunset, drawn by the coral pink hues above the horizon, and miss the more dramatic changes that are happening behind us. Here, we see a band of more muted amaranth pink, dubbed the Belt of Venus, illuminated by red sunlight that is not scattered in its passage through the atmosphere. Below is a rising purple swathe, that part of the visible sky that is in Earth's shadow. During civil twilight, only the very brightest stars and planets become visible.

Civil dusk signals the beginning of nautical twilight, which persists until the geometric center of the Sun is 12° below the horizon — nautical dusk. At nautical dusk, it's sufficiently dark that a sailor at sea would not be able to see the horizon, hence its name. Our monochrome scotopic (low light) vision begins to dominate and colors fade as everything on land takes on shades of grey. The purple in the east merges with darkening sky above. First-magnitude stars begin to appear. Initially they seem lonely points of light, but they gradually multiply as the sky darkens and fainter stars join them. Eventually, the entire Plough asterism in Ursa Major appears, pointing to Polaris, so at last we can polar align our equatorial mounts. Night is approaching, but the sunlit sky is still visible on the sunset horizon. The third phase, astronomical twilight, is beginning.

Light's last gasp

As the Sun descends past nautical dusk and into astronomical twilight, when our star is between 12° and 18° below the horizon, its illumination is replaced by other sources. For too many of us, this is the skyglow from artificial light, but even in unlit places on a Moonless night the sky is never completely dark. The combination of an imperceptibly faint auroral glow, the zodiacal light (sunlight reflected off interplanetary dust particles), and the light of diffuse matter in our Galaxy all contribute, though their contribution is less than that of a single mag. +6.5 star if it was distributed over an area the size of the Moon.

Astronomical dusk takes place when the Sun's geometric center drops to 18° below the horizon. Above our heads we will see, with dark-adapted eyes, objects as faint as we are likely to. Away from light pollution, the Milky Way shows structure sculpted by the dust of dark nebulae. The Andromeda Galaxy and the Double Cluster in Perseus may show themselves even without binoculars. The varied colors of stars become more apparent, and our awareness of the existence of artificial satellites and sporadic meteors grows. The glittering sky-dome above our heads appears to have come closer. This is night.

Then, all too soon, it is over. The sky brightens, the stars fade, the twilight phases play out in reverse. Dawn, and a brand-new day, is upon us.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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Our Fortunate Earth Our Fortunate Earth
Our Fortunate Earth

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Our Fortunate Earth

Our world would be a much more chaotic place if Jupiter's orbit was only slightly different.

earth

This color image of the Earth was obtained by Galileo on Dec. 11, 1990. Image credit: NASA/JPL

One of the central questions in planetary science, and the possibility of life elsewhere in the cosmos, is how ordinary our own planet is. Is Earth in some way in a special situation, offering unusually clement conditions for the emergence of life, or are there potentially multitudes of planets in our Galaxy that could be alive? This question is becoming more and more important in light of the fact that we continue to discover extoplanets. What features would these far-flung worlds need to offer the best hope for harboring extraterrestral life, and therefore which candidates should we shortlist for our follow-up telescopic observations of their atmospheres to look for signs of biology?

In particular, it's been argued that Earth may have offered an especially stable climate over the billions of years of its existence. Earth's climate has varied over planetary history — from the hot and humid times of the early Triassic period 250 million years ago, to the 'Snowball Earth' episodes when much of the world is thought to have frozen over. But overall, the terrestrial climate has remained remarkably stable. Some of the main drivers for a fluctuating climate, seen over the past few million years of the world swinging between ice ages and warmer interglacial respites, are the Milankovitch cycles. These are cosmic cycles in the eccentricity of Earth's orbit (how circular or egg-shaped it is), the planet's obliquity (how much its axis tilts), and the timing of the seasons — all affected by the gravitational influences of the other planets in the Solar System. The orbital eccentricity of Mercury, for example, varies far more than that of Earth. So the key question is, if the architecture of the Solar System was slightly different, how would this affect our world's orbit?

Jonathan Horner, at the University of Southern Queensland, and his colleagues have explored just this. They used a computer model of the Solar System to track how Earth's orbital oscillations changed as they tweaked the orbits of Jupiter, Venus or Mars in the Solar System, trying almost 40,000 different situations for each planet.

The most obvious result of their simulations, although not entirely unexpected, is that if Jupiter was slightly closer to the Sun it would completely disrupt Earth's stable orbit. Similarly, moving Venus further out than about 0.92 AU spells disaster. Interestingly, though, they did find that Venus and Earth could be stable even with both orbiting at 1 AU if they were located in a 1:1 orbital resonance — just like the Trojan asteroids in a locked orbit with Jupiter. This is one possibility for habitable worlds in exoplanetary systems with warm Jupiters.

The most important results, however, are the ones looking at more subtle shifts to Earth's Milankovitch cycles and how these might affect the planet's climate. The team intend to apply their modelling approach to Earth-like exoplanets, as and when they are discovered. Any worlds likely to experience more pronounced climate variability could have a lower chance of maintaining life, and Horner says that these can be ruled out and our attentions instead focused on the more promising worlds.

ABOUT THE WRITER
Lewis Dartnell is an astrobiology researcher at the University of Westminster and the author of The Knowledge: How to Rebuild our World from Scratch (www.theknowledge.org)

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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Imaging for Science, Asteroids Imaging for Science, Asteroids
Imaging for Science, Asteroids

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Imaging for Science, Asteroids

Pete Lawrence looks at how your images can help monitor the position of potentially hazardous objects crossing Earth's orbit.

asteroid

This computer-generated image depicts the flyby of asteroid 2014 JO25. The asteroid safely flew past the Earth on April 19, 2017 at a distance of about 1.1 million miles (1.8 million kilometers), or about 4.6 times the distance between Earth and the moon. Image credit: NASA/JPL-Caltech

Asteroids or minor planets are small Solar System bodies that are visible because they reflect sunlight. The larger members of this group have dimensions measured in hundreds of kilometers, but asteroids can be as small as 1m along their largest axis. Most asteroids are located in what's known as the main belt, a huge repository for such objects located between the orbits of Mars and Jupiter. In all but very rare circumstances, asteroids appear star-like through amateur scopes. Visually, they can be measured in terms of their brightness, position and occasional apparent interactions with other objects.

The sheer number of asteroids in orbit around the Sun means that occasionally we get to see one occult a distant star. Asteroid occultations provide an important way to determine the shape profile of these rocky bodies.

Accurate date and time recording is vital when observing asteroids, as it is this information which ultimately is used to refine the objects orbit and position.

Asteroids look just like stars when viewed through a telescope. It's only when their positions have been noted or photographed over an extended period — normally days — that their motion and true nature is revealed. Most asteroids appear to move slowly against the background stars but those that venture close to Earth may have enough apparent speed to appear to move in real time when viewed through a telescope or binoculars.

Bodies that have orbits bringing them close to Earth are known as near-Earth objects (NEOs) of which near-Earth asteroids (NEAs) are a subset. NEOs larger than 140m that cross Earth's orbit are classed as potentially hazardous objects (PHOs) and again, asteroids form a subset known as potentially hazardous asteroids (PHAs). To date, all known PHOs are PHAs.

Scientific asteroid images for astrometry and photometry need to record the body as a sharp dot without trailing. For slow-moving asteroids this may not be an issue, but fast movers require short exposures or setups that track the asteroid itself. This is especially useful for the high-cadence photometry necessary to determine the light curve, and hence spin-rate, of an asteroid.

For more general appeal, in outreach material for example, a fast-moving asteroid provides a convenient way to produce a trail that would otherwise take many extended exposures to capture. In this instance, a correctly polar aligned telescope tracking at the sidereal rate or, better still, autoguided on the stars, will produce a sharp star field with the asteroid as a light trail. A similar effect can be created by aligning shorter exposures on the stars, and stacking them with the brighter elements set to show through.

Many asteroids are within range of a basic telescope and DSLR setup. For scientifically calibrated work, CCD cameras, (preferably with specialist filters) are recommended. By using planetary imaging techniques, larger telescopes may even be able to capture larger asteroids as extended discs during favorable oppositions, rather than the usual star-like dot.

Project 2: Asteroid astrometry

Use software to help you plot the exact position of small space rocks

Measuring the position of an asteroid is an important step in determining and refining its orbit. This is especially true for asteroids on eccentric orbits, which have the capacity to pass close to Earth. Smaller bodies returning to the inner Solar System may have been gravitationally perturbed, leading to changes in the previously established orbit, and these need to be monitored.

The astrometry of asteroids is similar to comet astrometry, with the exception that asteroids are somewhat easier to measure, appearing as singular dots of light without the complexity that accompanies the expansive head of a comet.

It is recommended that serious astrometric measurements follow the guidelines set out by the International Astronomical Union's Minor Planet Center (MPC), available online at www.minorplanetcenter.net/iau/info/Astrometry.html.

The basic workflow for the astrometric measurement of an asteroid is quite straightforward. First you need to obtain a set of images that include the object you intend to measure. Then you'll need some software assistance to measure the position accurately; the shareware Astrometrica is highly recommended.

Astrometrica allows you to 'blink' your images, which should reveal the asteroid moving against the static star field. The software will need to identify the star field in the images in order to determine the asteroid's position. You can help here by manually identifying the star field and supplying Astrometrica with the correct RA and dec. coordinates for the center of the imaging frame. Once entered, the program attempts to match the star field.

If it doesn't quite get things right, you can adjust the alignment manually. Astrometrica's star template can be adjusted for scale with a focal length used setting, for rotation with a position angle setting and positionally with an onscreen arrow key pad. Once the alignment has been set, clicking on the object will generate an MPC compatible log file of positional data which can then be submitted according to the submission guidelines.

Project 3: Asteroid photometry

Accurately plotting of the brightness and shape of distant asteroids is a team effort

Occasionally an asteroid will pass in front of a star, dimming the star's light as it goes. There are numerous programs available to predict such events as well as websites, such as Euraster, which presents results without you having to having to calculate them yourself.

A typical asteroid occultation path will be a narrow track and may require you to travel to a specific location in order to view and record the event. This adds additional complexity in that it requires the use of a portable observing and recording setup and a means to accurately calculate your location and altitude. The modern way to do this is with some form of GPS recorder.

One of the hardest parts of observing asteroid occultations is to locate the star that is going to be occulted. This can be done using a Go-To system, but you often need to use very accurate star charts to augment the process, especially when the star to be occulted is very faint.

A common way to record asteroid occultations is with a low light video camera. The resulting video, normally recorded in the AVI format, can then be analyzed by specialist programs such as LiMovie or Tangra, which are both available for free.

A successful occultation should produce a light graph for the star that shows it dim as the asteroid passes in front of it and brighten as the asteroid moves out of the way. Accurate timing of the star's dimming will produce a line profile across the asteroid. Interesting though this is, such profiles really become useful when multiple observers record and communicate these events. With multiple profiles recorded, it's then possible to produce a more complete profile of the asteroid.

Obviously for this to be of any worth, a highly accurate time signal needs to be used. A device such as the International Occultation Timing Association's video time inserter (IOTA-VTI; https://occultations.org) is an ideal way to do this as it has the capability to insert coordinated Universal Time (UTC) on every frame of a recorded video signal.

ABOUT THE WRITER
Pete Lawrence is an expert astronomer and astrophotographer who holds a particular interest in digital imaging.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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The Wonder of Satellites The Wonder of Satellites
The Wonder of Satellites

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

The Wonder of Satellites

Astro imager Will Gater explores the photo opportunities presented by the myriad spacecraft that can be seen speeding overhead through the night.

asteroid

AEHF (Advanced Extremely High Frequency) Satellite. Image By USAF (Los Angeles AFB) [Public domain], via Wikimedia Commons

Nightscapes with a bit of Sparkle

Nightscape images that contain glinting Iridium flares or space stations have been a staple of astro-imaging for decades. For beginners, they're great targets to practice your skills on, and it's possible to get really striking images with a basic setup consisting of nothing more than a DSLR and tripod. If you have a bit more experience, don't dismiss shooting a satellite or space station; even advanced photographers can find fresh challenges in experimenting with the framing and foreground of such photos, and in finessing the quality of the final shot. Done well, these pictures can really spark the imagination in ways that other types of astro-images might not.

The timing, brightness and location on the sky of any potential Iridium flares is dependant on your location, so — just as with ISS and other bright-satellite passes — in order to find out when and where one will be visible from your site you'll need to consult a website like Heavens Above (www.heavens-above.com). Once you have this information you can set about planning your shot.

The free planetarium software Stellarium (www.stellarium.org) is particularly useful for this as you can use its plugins to overlay a rectangle showing the size of your camera's field of view on the sky. By cross-referencing the Stellarium view with the information and star chart from Heavens Above, you can identify the path and position of whichever satellite you're aiming to catch and try out different compositions. Stellarium can show the track of the ISS on the sky, and the paid app SkySafari Plus can also perform the same task.

Shooting a series of consecutive 10- to 20- second exposures at a mid-range ISO with a DSLR, kit lens and static tripod will pick up most bright satellite passes. With Iridium flares, aim to start capturing images about 90 seconds prior to the predicted flare time and end the series about the same amount of time after the flare reaches its brightest; this way you'll capture a pleasing trail that slowly builds in brightness, peaks, then fades away. You can then bring the series of images you've captured into processing or stacking software and combine them, so that the short trail in each photo joins the others to form a longer one.

Since most satellites zip across the sky, capturing a series of photos from a static tripod will result in gaps in the final 'combined' satellite trail due to the short delay between exposures. To get around this you can mount your camera on a tracking mount and take one, much longer, single exposure. This requires balancing the exposure length — which will need to be several minutes — with the lens aperture, ISO setting and sky brightness, but can produce attractive unbroken satellite trails against rich, starry skies. Remember, if you do this any foreground will be slightly blurred.

A Split-Second Spectacular

One of the most exciting areas of satellite astrophotography to develop in recent years is imaging the International Space Station passing in front of the Sun or Moon. Imaging these 'transits' requires extensive planning, but the resulting pictures are extraordinary. A typical transit might last seconds, — sometimes much less — and will only be visible from within a narrow strip of Earth's surface. To find out when an ISS transit is visible near your location you can use the excellent ISS Transit Finder (transit-finder.com). If you intend to image a solar transit, where the space station is silhouetted against the disc of the Sun, you'll need to use a certified solar filter for your telescope and be sureto remove any finderscopes. Here are the key steps required to capture this thrilling phenomenon with a scope and DSLR camera.

Step 1: Plan
Find out when a transit will be visible nearby using the ISS Transit Finder website. You may have to travel to be in a position to capture the event. Use planetarium software to check where in the sky the Sun or Moon will be.

Step 2: Setup
Next set up your scope and have it track at the solar or lunar rate (depending on your target). If you're imaging the ISS transiting the Sun, fit a specialist, certified solar filter and remove any finder scopes.

Step 3: Focus and exposure
Focus the view — use the terminator if viewing the Moon, or sunspot or the solar limb if viewing the Sun. Whether you capture stills or video, make sure that the exposure length is very short so that the ISS does not blur.

Step 4: Capture video or a rapid burst of stills
Start capturing video or a burst of stills as the moment of the transit approaches; that way if there is a slight error in your timing you'll still get the shot. For a DSLR video use the highest frame rate that the camera allows.

Step 5: Review, extract and process
Review and process the frames from our video or still images that show the ISS. Software such as PIPP (https://sites.google.com/site/astropipp) can extract still frames from videos. Then process and enhance the images.

Catch a Dragon

If, like us, you remember fondly the days of NASA's Space Shuttle, you may well recall that on occasions the spacecraft and its — just-detached — external fuel tank would be visible passing over the UK shortly after launch. There was nothing quite like watching the rocket roar off the pad live on NASA TV then seeing the very same shuttle and orange fuel tank — both appearing as points of light; the orbiter appearing white, the fuel tank a subtle ochre tint — silently glide overhead. Though the Space Shuttle is no longer flying, there's still occasionally a chance to catch a similar spectacle thanks to one of the new generation of ISS-servicing spacecraft: SpaceX's Dragon capsule.

Whether you'll be able to see the capsule on its way to the ISS just after lift off depends on the conditions of its launch. For the capsule to be visible, it needs to be dark or deep twilight in the UK, but the Dragon itself has to be in sunlight as it flies over. Helpfully, the CalSky website (www.calsky.com) publishes visibility predictions for some of the Dragon spacecraft around the time of scheduled launches to the ISS; you simply input your location details and it will tell you if the Dragon will make any visible passes. The pass you want to look out for — if it's listed — is the one that's about 20 minutes after the expected launch time, as that'll be the Dragon making its first flyover after departing the Florida coast. It's worth keeping an eye on either the NASA TV or SpaceX online video stream that usually accompanies the launch too, as it'll let you know if the lift off gets scrubbed.

One of the things that's so exciting about catching the ISS-bound Dragon just after lift off is that, from here in the UK, it's not just the capsule you get to see. Dragon is propelled into orbit by a SpaceX Falcon 9 rocket, and the separated upper stage of that rocket is visible next to the capsule as it passes over.

Not only that, but Dragon itself jettisons two solar-panel covers after lift-off and these appear either side of the spacecraft as two points of light which repeatedly brighten and fade during the pass as they tumble away. It's a truly electrifying sight and one that can be captured easily using a DSLR, static tripod and 50-100mm lens, and the same basic technique described in 'Nightscapes with a sparkle'. We've even been able to film Dragon firing one of its thrusters during a pass, using a DSLR and a telephoto lens.

The ISS up Close

Ordinarily, high frame rate cameras are used to create detailed images of targets like the lunar surface and planets. But it's also possible to use them to capture high-resolution shots of the ISS showing its modules and solar arrays.

The primary challenge with this type of imaging is tracking the rapidly-moving ISS, since most high frame rate camera and telescope combinations will provide a small field of view that is tricky to keep centred on the station.

Tracking is typically done manually with the help of an accurately aligned finderscope and the mount's handset set at the highest possible slew rate or, in some cases, carefully manoeuvring the telescope by hand. Essentially you start your computer recording a video from the camera and hope that at some point during the pass your guidance causes the ISS to race through the frame.

Focusing can be done in advance on a bright star — or even better, the Moon — while the correct exposure length will depend on the setup you're using; crucially it'll need to be short enough to stop the ISS from blurring and this may mean that you have to greatly increase the camera's gain to compensate.

Fade to Orange

The reason it's possible to see the ISS against the starry sky is that, at the altitude of its orbit, it's still illuminated by the Sun. Sometimes, however, the ISS will disappear into the darkness of Earth's shadow. Just before it does that you can see and image one of the most beautiful satellite phenomena of all: the ISS experiencing 'orbital sunset'.

As the station slips into the shadow, the Sun sinks below the Earth's limb as seen from the ISS in orbit. In the last moments leading up to that 'sunset' the whole structure is bathed in a deep-orange light. And because that light is the same sunlight that illuminates the station as it passes over us, from the ground the ISS turns from a brilliant white to a deep orange-red, before disappearing.

This effect can be seen clearly in binoculars from suburban sites, but is a particularly rewarding target for imagers and naked-eye observers under darker skies. The passes in which the ISS moves into Earth's shadow are clear in the night-sky charts that accompany each ISS pass prediction on Heavens Above (www.heavens-above.com); they're the ones where the pass seems to abruptly 'stop' amongst the stars. Point your camera in the direction of that end point and — with a long exposure of a minute or so using a DSLR on a tracking mount — you should pick up the gradual fade to orange in the ISS's trail.

What is an Iridium flare?

Iridium 'flares' appear as a brief and slow-moving point of light that brightens rapidly and fades just as fast. They are produced when the antennas of any of the numerous of Iridium communications satellites catch the Sun's light and reflect it back to Earth. In January, the first in a new fleet of Iridium satellites was launched. The antennas of these new satellites aren't as reflective, so the days of Iridium flares could be numbered.

ABOUT THE WRITER
Will Gater is an astronomy journalist, author and presenter. Follow him on Twitter at @willgater or visit willgater.com

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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The Sky in Motion at US Store The Sky in Motion at US Store
The Sky in Motion

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

The Sky in Motion

Astronomer Will Gater reveals the best way to observe and image transient and evolving celestial phenomena, and how you can help scientists in the process.

asteroid

This NASA Hubble Space Telescope set of images from Sept. 10, 2013 reveals a never-before-seen set of six comet-like tails radiating from a body in the asteroid belt designated P/2013 P5. Image Credit: NASA, ESA, D.Jewitt/UCLA

For most of us our interest in astronomy is, and hopefully will continue to be, a lifelong passion. In 10, 20, even 30 years from now we'll look up to the night sky and in the stars, galaxies and nebulae that fill our view we'll see old friends, unchanged over all that time. The truth is, of course, that the stars and galaxies we see are moving through space, and nebulae are evolving — they're just changes that are unfolding on an extraordinarily long cosmic timescale.

But that's not to say that we humans can't perceive any alteration or movement in the night sky. Quite the opposite. One could argue that the heart of amateur astronomy — and indeed one of the key elements of astronomy as a field of scientific study — is a rich and deep tradition of observing the changing night sky, from the appearance of comets to the monitoring of variable stars and the searches for supernovae in distant galaxies.

In the following pages we're going to explore some other transient and evolving celestial phenomena that you can observe and photograph with relatively simple equipment — the kind of kit that many amateurs have access to — so that you can see for yourself that the sky, and indeed the cosmos all around us, really is in motion.

Watch an Asteroid Whizz By

While the planets might be the quintessential 'wandering stars', drifting against the night sky's sparkling backdrop over weeks and months, there are other objects within the Solar System whose movement across the heavens is far more dramatic — so much so that their motion against the stars can be discerned over hours and minutes, rather than many days. Near-Earth asteroids are small, typically irregularly shaped bodies, whose orbits bring them relatively close to our planet at times. If a near-Earth asteroid is big and bright enough it can be a thrilling object to catch sight of in a telescope eyepiece, or capture on camera, as it makes a close approach. ESA maintains a database at http://neo.ssa.esa.int/web/guest/close-approaches that you can examine to see when any large, relatively, bright objects are next passing by — and of course the BBC Sky at Night magazine Sky Guide will usually contain news of upcoming notable near-Earth asteroid passes.

Capturing a Near-Earth Asteroid Pass on Camera

Watching a near-Earth asteroid slowly wander across a star field at the eyepiece can be tremendously exciting, but it's the sort of target that really requires a medium- to large-aperture instrument to be seen well. On the other hand, even a modest astrophotography setup can capture brighter near-Earth asteroids — here we explore how.

Step 1 — Equipment
Small refractors or Newtonians combined with a CCD camera or DSLR are well-suited to imaging bright near-Earth asteroids; we've even had success using just a DSLR and a 135mm telephoto lens. You'll also need a mount that can track the sky accurately for a few minutes at least.

Step 2 — Track and focus
Set up your imaging kit. If you're using an equatorial mount get the polar alignment (and thus the mount's tracking) as accurate as you can, as this will help both image quality and processing later on. Next, focus on a bright star — ideally with the help of a Bahtinov mask.

Step 3 — Locate and image capture
Use Stellarium (stellarium.org) and its Solar System Editor plug-in to find a near-Earth asteroid's location. Slew to the coordinates, take brief test exposures, then cross-reference the star field with Stellarium. When you've confirmed the near-Earth asteroid is in frame, check it's not moving out of shot. Capture a series of exposures.

Step 4 — Stack or animate
You should now have a set of images (typically taken over several tens of minutes) that shows the near-Earth asteroid moving between frames. You can now process and stack these together with your chosen image processing software to show the asteroid's path, or collect and save the frames as an animated GIF.

Marvel at a Lunar Sunrise

As astronomers we're familiar with the Moon's phases, caused by its movement around the Earth and the changes in illumination that come from the varying geometry of the Earth, Moon and Sun relative to one another. Prior to full Moon, the boundary demarcating night and day on the lunar globe, and the line that gives the phase its 'shape' — called the terminator — is the swathe of terrain where the Sun is rising over the lunar landscape. At this point in the lunar cycle the phase is waxing (growing), as the terminator travels across the disc. After full Moon the terminator moves westwards from the eastern limb once again, but is now where the Sun is setting, with the phase waning (shrinking).

This night-by-night movement of the terminator, and consequently the daily change in the lunar phase, is large and easily visible to the naked eye. But you can also observe and image subtle variations in the Moon's phase over the course of just one night. Watching the Sun rise or set over a chain of mountains or a large crater rim is a captivating observing experience; it is quite something to see the lighting change, and shadows lengthen or shorten. It's evidence of the Moon's orbital motion, happening right in front of your eyes.

The UK winter months, when the Moon is high for hours in a dark sky, are an ideal time to attempt the observation. Our favourite targets to see this phenomenon on are the large craters Copernicus and Plato — the latter especially, for the shadows from its rim that creep across its smooth floor — the lunar Alps and the Sinus Iridum.

A high frame rate camera and a modest amateur telescope can capture the changes easily. If you are able record an AVI video every 20-30 minutes or so for several hours, you can create dramatic animations of the changing illumination. This requires each processed image produced from the raw AVI videos to be brought into software — such as Photoshop or GIMP — as a separate layer. Multiple layers within a single picture can then be saved as an animated GIF file.

How You Can Help The Professionals

Taking pictures or making observations of some of the phenomena we've covered in this article can be an exciting experience in itself, but it's also possible that your records could help professional astronomers with their research. For example, if asteroid imaging is your thing, the scientists working on the OSIRIS-REx mission — which will return samples from the surface of the asteroid 101955 Bennu in 2023 — run a project called Target Asteroids! (https://www.asteroidmission.org/get-involved/target-asteroids) It uses data captured by amateurs to help learn more about certain asteroids. Alternatively, if you've been lucky enough to capture a picture or timelapse of the Northern Lights on holiday, the Aurorasaurus citizen-science project (http://aurorasaurus.org) is collecting images of a poorly-understood auroral phenomenon dubbed, rather unusually, 'Steve' — if your snaps show the unusual filamentary feature they could be useful to researchers.

And of course many national astronomical societies and organisations gather reports and observations of transient and changing astronomical phenomenon sometimes for publication and analysis in their journals.

So whether it's through a citizen-science project or a more traditional endeavour, like meteor counting, planetary imaging or variable star observing, there are many ways that we amateurs can make a meaningful contribution.

The Spectacular Seething Sun

We needn't look lightyears out into space to find evidence of the dynamic and ever-changing nature of the cosmos we live in. In fact you'll find it on our celestial doorstep in the form of our star, the Sun. This seething ball of plasma is constantly changing. Its churning 'surface' — the photosphere — is occasionally pockmarked by dark, transitory, blemishes known as sunspots, while above huge tendrils of plasma, called prominences, rise and waver as they are corralled by the star's magnetic fields.

To observe these features safely however you'll need specialist equipment. To study the photosphere, for example, a telescope needs to be fitted with a certified solar filter and any finder scopes should be removed too. With careful and correct use and installation — conforming to the manufacturer's instructions — certified solar filters can provide superb views of evolving sunspots and large sunspot groups.

There are also specialist dedicated solar telescopes available which, as well as filtering the Sun's light so it is safe to view, show only certain specific wavelengths of the Sun's radiation. One type of dedicated solar telescopes shows what's known as the 'hydrogen-alpha' band in the Sun's spectrum. These solar scopes reveal a layer in the Sun's atmosphere known as the chromosphere and in doing so open a window onto one of the most dynamic regions of our star.

While an ordinary certified solar filter will show the solar photosphere as a smooth whitish or yellowish disc, perhaps marked by sunspots or speckled bright patches known as faculae, a hydrogen-alpha solar telescope will show the Sun's chromosphere as a bright, scarlet-red globe shrouded in a mass of plasma 'fibres'.

A hydrogen-alpha solar telescope will also often reveal the prominences leaping off the limb of the Sun, and these can change in literally a matter of minutes, meaning they are a wonderful target for high-resolution imaging where spectacular animations can be made of their evolution. Sketching can be a great way to record the changes in these features too.

The powerful magnetic fields associated with sunspots also have an effect in the chromosphere. There they manifest themselves as bright 'active regions' where loops of plasma twist and turn around the dark sunspots. Like prominences these too can change and evolve over short periods. Sometimes they may even exhibit very bright, fleeting, beads or filaments of light. These are thrilling events for solar observers and imagers, and are known as solar flares.

Create a Timelapse of the Turning Sky

One of the most obvious signs that we live on a rock spinning in space is the motion of the stars across the sky during the course of a night. This movement is a result of Earth rotating on its axis, and you don't need a hugely advanced setup to capture it on camera; a DSLR, wide kit lens and static tripod are ideal for tackling a classic star trail shot. Leave the shutter open for 30-60 seconds and the rotation of the Earth will blur the stars into short arcs. If you want to take things a step further, try creating a timelapse of the sky — and perhaps the Milky Way too — moving. You can use the same kit as for a star trail shot, but you'll need to approach the way you capture the images in a slightly different way. For timelapses you don't actually want the stars to trail. What you need are for them to be points of light so that when you come to animate the shots it looks almost as if the sky is a static picture that's drifting over a landscape. This may mean that you have to keep the exposure length short, increase the ISO and open your lens's aperture right up to compensate. When you've found the right settings, set the camera taking exposures continuously, say for 30 minutes for a short timelapse. You'll typically capture hundreds of photos doing this, so make sure your camera's memory card and your computer are up to the task! The images can then be processed as a group in image processing software and then imported into a video editor to be animated into a smooth video. There are numerous ways of achieving the latter — for example in iMovie you'd do it by setting the 'duration' of each still image to 0.1 seconds. This technique can also be used to make timelapses of other dynamic astronomical phenomena, such as aurorae and noctilucent clouds.

The Skies In Motion This Month

A particularly fine chance to watch the motion of the heavens is on offer in the UK this month when, in the early hours of the morning on 6 November, the gibbous Moon will occult (slip in front of) the bright star Aldebaran in Taurus. As the Moon journeys across the background stars of Taurus, Aldebaran will disappear behind the brightly lit western limb of the Moon, emerging 40-60 minutes later from behind the unlit eastern limb. Occultations are great events for video astronomy, so if you have a digital camera that can shoot video try capturing Aldebaran suddenly popping into view as it reappears from behind the Moon. The exact moment of Aldebaran's reappearance (and disappearance) will depend on where in the UK you're observing from, so consult a planetarium programme, such as Stellarium (http://www.stellarium.org), for location-specific times.

ABOUT THE WRITER
Will Gater is an astronomy journalist, author and presenter. Follow him on Twitter at @willgater or visit willgater.com

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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Chasing the Moon's Shadow Chasing the Moon's Shadow
Chasing the Moon's Shadow

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Chasing the Moon's Shadows

This summer, Elizabeth Pearson travelled across the US to hunt down the total eclipse of the Sun on 21 August 2017.

Mars

By Zombiepedia - Own work, CC BY-SA 4.0, Link

In 1999, a total eclipse of the Sun passed over Cornwall. And I missed it. Ever since, I have wanted to see totality, and so when I heard that the Moon's shadow would be passing coast to coast over the US mainland on August 21st 2017, I knew I had to be there. I decided to take a road trip that would end up taking me almost 3,000km across the country as I attempted to chase down the lunar shadow.

My journey started in Salt Lake City, Utah, where I picked up the hire car that would prove to be my faithful steed for the week. My first stop was Salt Lake City's Clark Planetarium, where I found queues out the door. The crowds had been brought in by an email from a major online retailer recalling eclipse glasses, sparking a panic.

"A lot of people who thought they had glasses just got emails saying their glasses cannot be trusted, and have come to the Clark Planetarium because we have the real ones. We never thought we'd be the only supplier in town. We have a supply for today, we may even have a supply for tomorrow, but then who knows," says Seth Jarvis, the director of the Clark Planetarium.

Like most of the nation, Salt Lake City would only see a partial eclipse, making appropriate eyewear crucial. But for me, the 91 per cent it would see wasn't enough. I wanted totality. It was time to start chasing that shadow.

As I drove from Utah into Wyoming, I began to see signs that I was heading into totality country. On the highways there were notices banning heavy vehicles on August 20-22 to keep traffic moving, while in towns handwritten signs offered eclipse parking. Every business, it seemed, had special 'Totality Deals'.

The Building Buzz

Eventually I made it to Casper, Wyoming, the largest town on the eclipse's central line and host to the Astronomical League's annual AstroCon convention — which happened to coincide with my visit. The event had drawn people from all over the world, keen to see the eclipse.

"Once you've seen totality, you've just got to see it again," says Sue Baldwin, an eclipse chaser from Auckland, New Zealand. "The first time I saw it I bawled my eyes out for 30 seconds, and actually had to hit myself so I could look at the totality. It's just that emotional, there is no comparison."

With so many eclipse enthusiasts together under one roof I couldn't help picking up on their excitement. And it only grew when I drove on to my next pit stop of Alliance, Nebraska. "They're saying that there are going to be 20,000 people in town altogether," says Jessica Hare, the acting manager for local monument 'Carhenge', a replica of Stonehenge made from scrap cars and the reason this remote location is so busy when I arrive.

"For the most part people in town are excited. There's a reason we live here, though: we're not into big crowds," Hare continues. "But it's a change of pace for a few days and then we've got something to talk about for 60 years."

With only two days to go, people were already arriving and setting up camp. But amongst the bustle, an air of disquiet was beginning to form. People were checking the weather and all was not well. On August 21st, clouds were forecast across the eastern side of the US. Combined with the eclipse glasses scare, it looked like huge numbers of people might not get to witness the great event.

By the time I reached Sutherland in central Nebraska, where I had planned on watching the eclipse, the forecast had grown even worse. The nearest place with completely clear skies forecast was almost 400km back the way I had just come, along roads already gridlocked with traffic. Did I stay and risk being clouded out, or go and risk getting stuck on the highway?

I had come too far to end up staring at clouds. Time to chase those clear skies. Wanting to avoid the most horrific traffic, I picked a town just off the centerline and at 4am on 21 August, I was back in the car.

As I set off, the fog was so thick that at times I could barely see 30m ahead of me. But I was determined to beat the clouds and fought on until four hours later I reached my final destination — an old airfield in Mitchell, Nebraska. A few hundred people had already arrived, most of whom had also undertaken long treks, and were ready to see their first eclipse when it started at 10:25am.

The Moment of Darkness

When the hour came, we donned our (certified) eclipse glasses to watch as the Sun was slowly eroded away by the Moon. As the spectacle unfolded, the dwindling sunlight made its effect felt. The air, which should have been uncomfortably hot by now, felt more like a breezy afternoon.

With around 20 minutes to go, I reached to take my sunglasses off before realising I wasn't wearing them. The light was fading and taking the colour out of the world with it, like an old photograph that's been left in the Sun.

At 11:46am, with one minute left, the Sun was down to the merest sliver. I turned to the west to watch as a wall of darkness seemed to advance across the sky.

Turning back, I watched as a sudden explosion of diamond light came from the Sun as the last of its rays were covered, accompanied by a huge cheer from the crowd.

Where once the Sun had been, there was now a hole of utter blackness. A crown of light danced around it and I could almost see the fine tendrils swaying with the breeze. It seemed huge, stretching over a much larger area of sky than I'd expected. Around me, the sky was in twilight with pink trimming every horizon, as if the Sun had just set in all directions together.

The crowd was quiet now. After all the excitement and panic, I felt a sense of quiet calm. I was under the shadow of the Moon, watching plasma arcing a million kilometres out of the Sun. It was humbling, a reminder of our small place in the grand Universe.

The Chance of a Lifetime

All too soon, I could tell totality was reaching its end. The perfect circle of blackness was beginning to look lopsided. One minute, 53 seconds after the first, there was a second burst of light as the shadow passed, sweeping across the nation and taking the spectacle to the millions who waited farther east. As others rushed home, I stayed to watch as the Sun returned, taking a moment to appreciate what I had just witnessed.

Later that evening, back in Sutherland (where the weather had been perfect, of course), I headed out to look at the Milky Way, knowing our Galaxy is only one of billions that all move together in the ballet of the Universe. I've devoted my life to studying that dance, but I have never grasped its majesty like I did in that one minute and 53 seconds.

Once you've seen totality, you really do have to see it again. On April 8th, 2024, another eclipse will sweep across the US and I plan on being under the Moon's shadow once more. Maybe I'll see you there.

Stargazing Central

Sandhills, NE
The rural state of Nebraska is home to some of the darkest accessible skies in the world, making it a dream destination for deep-sky imagers.
https://visitnebraska.com/stories/visit-the-sandhills

Strategic Air and Space Museum, Omaha, NE
The museum is home to several space artefacts and a tribute to Nebraskan astronaut Clay C Anderson, as well as dozens of aircraft.
http://sacmuseum.org

Clark Planetarium, Salt Lake City, UT
As well as shows in the dome, the Clark Planetarium houses a space museum with interactive exhibits to enthuse little astronomers.
https://slco.org/clark-planetarium

Yellowstone National Park, WY
Spend the days exploring the world-class park and the nights taking in the dark skies. An astronomy program runs in summer.
www.nps.gov/yell/index.htm

Carhenge, Alliance, NE
This huge replica of Stonehenge made from cars was built in 1987 as a tribute to the artist's father, and has proved to be a popular road trip stop ever since.
http://carhenge.com

Craters of the Moon, ID
Follow in the footsteps of the Apollo 14 crew, who underwent geology training in this volcanic landscape prior to their trip to the Moon.
www.nps.gov/crmo/index.htm

ABOUT THE WRITER
Dr Elizabeth Pearson is BBC Sky at Night Magazine's news editor. She gained her PhD in extragalactic astronomy at Cardiff University.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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Why We've Got to Get to Mars Why We've Got to Get to Mars
Why We've Got to Get to Mars

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Why We've Got to Get to Mars

He may be one of the most famous moonwalkers, but Buzz Aldrin has spent the past 30 years developing a plan to get people to Mars. He tells Jamie Carter why.

Mars

By ESA - European Space Agency & Max-Planck Institute for Solar System Research for OSIRIS Team ESA/MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA - http://www.esa.int/spaceinimages/Images/2007/02/True-colour_image_of_Mars_seen_by_OSIRIS, CC BY-SA 3.0-igo, Link

Colonising the Solar System is becoming the 'in' thing among billionaires. SpaceX supremo Elon Musk recently talked putting a million people on the Red Planet within 100 years, while Blue Origin's Jeff Bezos thinks he can help spread a trillion people throughout the Solar System. That's big talk, but there's one man who's spent the last three decades telling anyone who'll listen about his plans to go to Mars, and why it's so important we do so.

"I'm 87 years old and I'm getting impatient," says Dr Buzz Aldrin, who walked on the Moon in 1969 as part of Apollo 11. "We've been stuck in low-Earth orbit for too long and I believe that we need to break this malaise," he says. "I do believe we can establish permanent habitation on Mars by 2039, and I have a plan to achieve it."

If that date seems rather specific, there's a good reason for it: it would be the 70th anniversary of Apollo 11's Moon landing. Not that Aldrin wants to be constantly reminded of that. It may be regarded as a seminal moment for humanity, but only until someone sets foot on Mars. "I want to be remembered as the man who led the world to Mars, for a permanent settlement," he points out.

Occupation vs. Exploration

Aldrin, who is constantly refining the ideas he first set out in his 2013 book Mission to Mars: My Vision for Space Exploration, now wants to play a pivotal role in the push to the Red Planet. But there remains a fundamental question: why do we need to occupy Mars? Why not just pay it a quick visit?

"What concerns me most about expeditionary missions is that we may go there once or twice and never go back — it would be flags and footprints again," says Aldrin, citing the Apollo Moon landings, the last of which was 45 years ago. "But the more important reason is that it's vastly more expensive to send people up there with all their infrastructure in one spacecraft and the quality of the science would be dramatically lower."

According to Aldrin, once you have the right kind of surface and transportation infrastructure, the cost of sending individual astronauts would be affordable. His is a pragmatic plan built upon orbital calculations that could make inhabiting Mars far more affordable than anyone imagines.

Aldrin's idea revolves around the concept of 'Cycling Pathways': one or possibly two Earth-Mars spacecraft (a 'Cycler') that travel constantly between Earth and Mars. "The astronauts will be transported to the Earth-Mars Cycler with a single launch, with refuelling in Earth orbit," explains Aldrin. "Using spacecraft that cycle between Earth and Mars would be an order of magnitude cheaper than using an entirely new series of rockets to send each crew to Mars."

Following on From Von Braun

Although his ideas pre-date those currently being proposed by various billionaires, Aldrin is certainly not the first to consider how to carry out a manned mission to Mars. Dr. Wernher von Braun, developer of the Saturn V rocket, briefed NASA's Space Task Group just after the Moon landings on a plan to land two expedition spacecraft on Mars in 1982. "Werner von Braun's vision of Mars exploration was a tremendous inspiration to many of us," says Aldrin. "But von Braun was really interested in using very large rockets. I think we can get to Mars without the same reliance on state-developed and operated rockets." Aldrin's plan also differs from Von Braun's in its level of reusability.

Ambitious space exploration plans always come with a huge caveat: politics. Aldrin was recently at the White House, standing alongside President Donald Trump as he signed an executive order re-establishing the National Space Council after its 24-year hiatus, but he's not getting too carried away with that decision. "I don't expect the Space Council to fundamentally change the US space programme by itself. But it will really become critical if the administration decides to fundamentally rethink major aspects of our civil and national space programmes," says Aldrin. That's what he's hoping for.

Aldrin will be keeping a close watch on what President Trump says on 24 July 2019 when the world marks 50 years since Aldrin and Neil Armstrong set foot on the Moon. "I'm personally very committed to the idea that the President should, and indeed must, announce a major US commitment to Mars permanence by the 50th anniversary", he says. "It's essential to force us to make the hard choices we must make in order to get to Mars in the next 20 years."

ABOUT THE WRITER
Jamie Carter is the author of A Stargazing Program for Beginners: A Pocket Field Guide and edits WhenIsTheNextEclipse.com

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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Secrets Erupt from Jupiter at US Store Secrets Erupt from Jupiter at US Store
Secrets Erupt from Jupiter

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Secrets Erupt from Jupiter

In January 1979, after a journey of 15 months, Voyager 1 began to photograph the first planet on its Grand Tour, the gas giant Jupiter. Voyager 2 followed a few months later, and together they rewrote almost everything we thought we knew about the Jovian system — not least the fact that volcanism exists beyond Earth.

Jupiter

Photograph by Cherdphong Visarathanonth in Prawet district, Bangkok, Thailand

At first glance, it resembled nothing more than a blemish on Voyager 1's lens. But as 26-year-old engineer Linda Morabito peered closer at the image of Jupiter's moon, Io, she realised she was looking at something extraordinary. The blemish was actually a faint, bluish crescent that was protruding from beyond the moon's limb.

This all occurred on 9 March 1979, four days after the probe had made its closest pass — 349,000km — of the broiling Jovian cloud tops. Morabito was part of the optical navigation team, plotting Voyager 1's trajectory to Saturn, three-quarters of a billion kilometres and 20 months away. She had just made the most significant discovery of the entire mission.

The long-exposure shot, taken a day earlier, viewed Io from a parting distance of 4.5 million km. Analysis revealed the crescent to be a plume — rising over 280km into space — from a volcano. Later named 'Pele' after the Hawaiian goddess of volcanoes, it was the first of hundreds of such features to be found on Io. As the days wore on, infrared data pinpointed regions rich in sulphur dioxide, where temperatures soared up to 200°C higher than the surrounding terrain. Four months later, on 9 July, Voyager 2 revealed that Pele had fallen dormant, although several other volcanoes remained active.

Big Surprises

It was a big surprise on a natural satellite with a size and density roughly equal to that of our geologically inactive Moon. Io's proximity to its giant host (it orbits just 421,800km from Jupiter's centre) forces it to bear the brunt of a punishing magnetic field. This is hundreds of times stronger than Earth's and 'co-rotates' with Jupiter's interior every 10 hours, transporting vast quantities of energetic plasma back and forth along magnetic field lines. The field is inflated at the magnetic equator, pushing the plasma outwards in a huge, tilted 'sheet' that rises and falls, flopping north then south, during each rotation period.

The relationship between Jupiter and Io is a complex one. As Jupiter's magnetic field sweeps past Io it strips 1,000kg of mass from the moon every second. This forms a doughnut-shaped 'torus' of charged particles, the existence and extent of which was first inferred by Pioneer 10. Ground-based observations also identified a neutral sodium cloud around Io, formed by atmospheric sputtering, as well as the spectroscopic fingerprints of sulphur dioxide.

Not until the discovery of Io's volcanism did the process of how this torus was maintained begin to make sense. Under Voyager 1's gaze, twice-ionised oxygen and sodium atoms glowed brightly at ultraviolet wavelengths. To achieve such intensities, electron temperatures have to surpass 100,000°C and radiate a trillion Watts — double the power-generating potential of the entire US — along a 'flux-tube' into Jupiter's magnetosphere. Voyager 1 tried to fly through this flux-tube, but missed its centre by around 5,000km.

Lava Lakes and Lights

Morabito's chance discovery identified Io as the most volcanically active place in the Solar System. It yields twice as much energy as all of Earth's volcanoes combined, despite having a fifth as many hotspots and being only a third of the size of our planet.

Voyager 1 found virtually no impact craters on its young and dynamic surface, just a few per cent of which was pockmarked with dark-centred volcanoes. From these snaked red and orange lava flows, some fanning out in wide arcs, others forming a series of twisting tentacles. Pele was surrounded by a hoofprint-shaped lake of sulphur dioxide, while 200km-wide Loki — more powerful than all of Earth's volcanoes, put together — had increased in magnitude and evolved into a two-plume eruption by the time Voyager 2 was able to observe it.

Jupiter's torus offered a contributing reservoir of energetic particles, which spiralled along magnetic-field lines to fuel the planet's spectacular aurorae. One display extended 30,000km across its north polar region and generated extraordinary 'whistling' radio emissions. The Voyager 1 image that confirmed the existence of the 'Jovian Lights' also picked out massive electrical discharges from 19 lightning 'superbolts', while Voyager 2 went on to locate eight additional flashes.

Jupiter's magnetosphere is a truly colossal powerhouse. The Pioneer probes revealed its sunward extent and raised speculation of a bullet-like 'magnetotail' in its wake. Voyager data confirmed the tail's existence and showed that it extended 740 million km beyond the planet, as far as Saturn's orbit. Increased solar activity since 1974 had compressed the sunward boundary and a continuous push-pull dynamic saw both spacecraft repeatedly enter, exit, then re-enter the magnetosphere — Voyager 2 recorded 11 boundary crossings. This showed the variability of the magnetosphere's size, as the boundary rhythmically flashed in and out in response to solar wind pressure.

Moving Pictures

The two Voyagers spent months examining Jupiter, both before and after their closest passes. From January until April 1979, Voyager 1 transmitted data across the 778-million-km gulf to Earth, while Voyager 2 did likewise between April and August. Pictures received during those periods showing how the differential rotation of Jupiter's atmosphere produces a colorful latitudinal display of bright 'belts' and dark 'bands', prompted comparisons to the work of Vincent van Gogh.

Movies made with overlapping photos of Jupiter's rotation showed clouds swirling around the edge of the planet's famous Great Red Spot and clipping along at 100m/s. Twice the size of Earth and observed telescopically since the 17th century, the spot inhabits the southern hemisphere and rotates anticyclonically, bearing many hallmarks of a high-pressure region. With no solid surface or continents to anchor pressure waves, Jupiter's storms can (and do) endure for centuries. The Pioneer probes saw uniform color within the spot and its attendant clouds, but by 1979 south temperate latitudes had altered considerably, producing complex turbulence. In July, Voyager 2 hurtled past at a distance of 576,000km and revealed a notable 'thinning' of bands at the spot's southern rim, a spreading-out of clouds to the east and a greater evenness of color. Three oval-shaped white spots, first seen four decades earlier and each the size of our Moon, had also worked their way steadily eastwards.

A Ring Is Revealed

At 1,300 times the size of Earth, Jupiter is the biggest and most massive planet in the Solar System. Infrared data from Voyager pegged its composition at 87 per cent hydrogen and 11 per cent helium, with trace amounts of methane, water, ammonia and rock. A seething mass of clouds, storms and eddies within its bands and belts moved crisply across its disc, indicating that the motion of material, rather than energy, was at work deep in the interior. Westward-blowing zonal winds extended at least 60° north and south, far closer to the poles than expected. But the surprises didn't end there.

Before 1979, only Saturn and Uranus were known to have rings; theoretical models of long-term stability had not predicted any to exist at Jupiter. That prediction was proven wrong just 17 hours after Voyager 1 made its closest approach, when a photo taken to search for new moons picked out a tenuous ring only 30km wide.

It was intrinsically dark and composed of tiny, rocky grains, with a reddish hue similar to the surfaces of the newly found moons Thebe, Metis and Adrastea. Long-range imagery also revealed a red surface on the elongated and cratered moon Amalthea. This prompted speculation that the ring might have evolved from an ancient moon torn apart by tidal forces and it was argued that Adrastea could provide a suitable reservoir of material for it.

Voyager 2 revealed the ring to be quite narrow — one scientist called it "ribbon-like" — and its proximity to Jupiter implied that it was quite young. Its main body was joined by an interior 'halo' of dust and an outer 'gossamer' ring, which petered out into the background darkness, 180,000km above the planet's cloud tops.

New View, New Details

The Voyager probes unveiled the Jovian system in its entirety for the first time and showed us the vast differences between the four Galilean moons. Even the finest telescopes of the era were only capable of showing Io, Ganymede, Europa and Callisto as tiny, dancing points of light. The two Voyager spacecraft revealed them to be four distinct worlds that varied in size from smaller than our Moon to almost as big as Mars.

Giant Ganymede is the largest planetary satellite in the Solar System, with an equatorial diameter of 5,270km, slightly pipping Saturn's moon Titan. Voyager 1 uncovered the presence of a thin atmosphere on Ganymede with a pressure equivalent to just one billionth of the sea-level pressure on Earth. Images taken by the probe showed a terrain split between dark, heavily cratered ancient areas and brighter, more youthful patches intersected by ridges and furrows.

The dominant feature on Ganymede's surface is the Galileo Regio, a 4,000km-wide dark patch big enough to cover the 48 adjoining US states. This vast oval-shaped remnant of Ganymede's primordial crust is punctuated by craters nicknamed 'palimpsests', after pieces of reused medieval parchment that allow the original, partly erased work to show through the new writing. The region and its craters offer a tantalising glimpse of Ganymede's past tectonic upheavals. Elsewhere, younger craters exhibit dark rays, extending for hundreds of kilometres across the surface.

An Old Moon

Callisto, although eight per cent smaller in equatorial diameter than Ganymede, was expected to be similar, as both moons are approximately half-water and half-rock and, unlike Io, are far enough from Jupiter to escape serious magnetospheric bombardment. Voyager 1 saw Callisto on the outward leg of its journey and found a surface without high mountains or deep ravines but dominated by the 600km-wide bullseye of the Valhalla impact crater and its surrounding array of concentric rings.

Vast tracts of heavily pitted terrain revealed a world whose origin may stretch as far back as the accretional stages of the giant planets themselves, some 4.5 billion years ago. 'Large' craters, exceeding 150km in diameter, were conspicuously absent, however, leading to theories that Callisto's ice-rock composition had somehow altered the ability of its thin crust to support them. Even at the time of the Voyager encounters, it was argued that ice floes over millions of years probably filled and obliterated craters of this size.

As for Europa, the two spacecraft saw the smallest Galilean moon as a highly reflective globe, reminiscent of a "string-wrapped baseball". It was a description inspired by the moon's striking linear features, from its scalloped ridges to meandering dark stripes that crisscrossed the surface for thousands of kilometres, while mysterious 'triple bands' made up of two parallel ridges, separated by a depressed central gorge. One of the few craters on Europa is 26km-wide Pwyll, which is surrounded by bright rays of ejecta that run for hundreds of kilometres out from its central basin.

Interestingly, the Pwyll impact seemed to have occurred on a particularly thin portion of the crust, for iceberg-shaped chunks of subsurface material protruded from its floor. Dark areas, nicknamed 'maculae', were identified as potential upwellings from deep within Europa's interior, while the side of the moon, which faces away from Jupiter was characterised by huge, wedge-shaped bands, many kilometres long.

More to Discover

The Voyagers' discoveries at Jupiter underlined the unpredictability of planetary exploration, for the largest planet in the Solar System had begrudgingly surrendered only a handful of the mysteries it held. For the Voyager scientists, it had been a once-in-a-lifetime experience. NASA's associate administrator for space science Thomas Mutch likened it to "being in the crow's nest of a ship during landfall and passage through an archipelago of strange islands". Volcanism on Io, colossal polar aurorae, along with unknown and unseen rings and moons could never have been confidently predicted before we turned our knowledge-gathering capabilities over to the Voyager robots, millions of kilometres from home; robots whose findings rewrote the textbooks on Jupiter for the next quarter of a century.

The Radiation Problem

Before 1970, it was theorised that large quantities of abrasive dust might endanger a spacecraft as it attempted to pass through the asteroid belt between Mars and Jupiter. Several years later, when the Pioneer probes crossed the belt, they showed the dust was no danger. But upon their arrival at Jupiter, a new problem emerged: the Pioneers' circuits had been fried and their optics darkened by the savage Jovian radiation belts. They'd endured 1,000 times the human-lethal dose of high-energy protons and electrons.

As well as building a plasma-wave instrument to analyse this environment, engineers worked to toughen the Voyager probes' electronics ahead of their visits to Jupiter and Saturn. Radiation-resistant materials, including tantalum, were tested to maximise their reliability, before being added into each of the spacecraft. Particularly sensitive areas received additional spot-shielding.

The Voyagers made it through the radiation belt but not wholly unscathed. Voyager 1 experienced a 'timing offset', which caused its on-board clock to slow down. Moreover, its two computers drifted out of synchronisation with each other and the flight data systems. These glitches led to some photographs being taken 40 seconds too early, which induced blurring and the loss of high-resolution images of Io and Ganymede.

Fortunately, Voyager 2 passed Jupiter at a much wider distance than its twin so its problems were correspondingly lessened. Its computer had also been reprogrammed to synchronize automatically, every hour. In this fashion, the complications of image-smear by the high radiation levels were largely avoided.

A Fresh Glimpse Of An Old Great

Measuring 26,000km in its east-west diameter and half as much north-south, the enigmatic Great Red Spot lies 22° south of Jupiter's equator and has been observed telescopically for more than three centuries. Its discovery is usually attributed either to the English scientist Robert Hooke or the Franco-Italian astronomer Giovanni Cassini, both of whom are believed to have seen and recorded it between 1664 and 1665. Writing in the Philosophical Transactions of the Royal Society, Hooke identified the feature's presence "in the largest of the three observed belts of Jupiter" and noted that "its diameter is one-tenth of Jupiter".

The spot was seen intermittently up until 1713, before seemingly vanishing. Heinrich Schwabe saw it again in 1831. Since then, it has changed both in size and color: ranging from an extraordinary brick-red hue to a more mellow ruddy brown and swelling at one stage to 40,000km in diameter. Voyager observations revealed it to be a high-pressure region, significantly colder at the cloud-tops, although the reason for its color remains a mystery.

Due to the lack of solid surfaces on the giant planets, long-lived storms of this type have been identified on Saturn and Neptune, although not in the same league as the Great Red Spot. It's possible that such features draw energy from the sides or below, or perhaps that they accrue their size simply by gobbling other smaller spots and eddies. It seems that thanks to the immense depth of the atmosphere and the absence of continents to dissipate the storm's energy, the Great Red Spot has settled into a semi-stable state.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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Titanic Discoveries at Saturn Titanic Discoveries at Saturn
Titanic Discoveries at Saturn

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Titanic Discoveries at Saturn

Long regarded as the 'wow' planet of the Solar System, Saturn proved more magnificent than anyone had imagined. While it was in the neighbourhood, Voyager 1 skimmed past Titan, still the only moon we know of with a thick atmosphere.

Saturn

Photograph by Cherdphong Visarathanonth in Prawet district, Bangkok, Thailand

On the evening of 6 November 1980, less than a week before reaching Saturn, Voyager 1 fell abruptly, though not unexpectedly, silent. Bruce Murray, then serving as director of the Jet Propulsion Laboratory (JPL) in Pasadena, California, was not alone in having expressed consternation over the hazardous manoeuvre that was about to take place. After all, the tiny spacecraft was three years into an epic mission of exploration that had already rewritten the textbooks on Jupiter. Now, more than 1.4 billion km from Earth, it was having its critical communications link with Earth intentionally severed so the craft could be turned towards Titan.

"Isn't it risky," Murray asked at one of the last pre-Saturn meetings, "to break communications, so close to encounter?" It was indeed a dauntingly bold move, but there was a clear rationale for it. Voyager 1 was following a route known as 'Jupiter-Saturn-Titan' so it could observe, at close quarters, the only natural satellite in the Solar System definitively known to possess a dense atmosphere.

If it was to fly within 3,900km of Titan's soup-like canopy of gases and particulate haze, a trajectory-correcting firing of the spacecraft's thrusters was needed. And to accomplish that, Voyager 1 had to reposition itself a quarter-turn away from its lock on Earth.

The Deep Space Network's tracking station in Goldstone, California, duly transmitted the requisite commands up to the spacecraft. It took 84 minutes, travelling at the speed of light, for those commands to cross the immense gulf between Earth and the Saturnian system.

Voyager 1 responded crisply, rotating its high-gain antenna away from Earth. Its hydrazine-fuelled thrusters hissed for almost 12 minutes, affording it a slight sideways nudge for the Titan flyby. The probe then realigned itself with our world. To everyone's immense relief, communications were restored 84 minutes later.

Investigations Begin

The first dividend was paid soon after. Early on 11 November, the spacecraft's radio signal passed through Titan's thick orange clouds, gradually faded and then vanished, reappearing after 13 minutes. The signal's 'occultation' allowed investigators to show that Titan's atmosphere — first detected spectroscopically in the 1940s — was far more substantial than anticipated. Later analysis of the signal data revealed the existence of a solid surface with a temperature of –180°C.

The radio signal also showed the moon to have an equatorial diameter of around 5,150km. This was a significant find as, until 1980, the unknown size of Titan's opaque veil had spawned the erroneous assumption that it was the biggest natural satellite in the Solar System, larger even than Jupiter's moon Ganymede. An occultation of our Moon, seen from Earth a few years earlier, suggested an optical size of 5,800km, but this figure was biased by a lack of precise detail regarding the thickness of Titan's clouds. With Voyager 1's data, it was possible to ascertain that Ganymede is marginally the larger of the two, and that both moons are bigger than the Solar System's innermost planet, Mercury.

Titan's equatorial tilt causes distinct seasons and Voyager 1 was able to show that gases and particulates migrate from one hemisphere to the other. Along with the sheer density of the atmosphere, this highlighted broad differences in albedo. Neither Voyager 1 nor Voyager 2, which swept 907,000km past Titan in August 1981, saw any trace of a solid surface through the murk, but they did identify a dark brown 'hood' of detached haze over the north pole. This contrasted starkly with the far brighter south and provided a glimpse of the seasonal variation — at the time it was spring in the north and autumn in the south.

The moon's atmosphere was known to contain methane long before the Voyager probes arrived, although it turns out that methane only accounts for a few per cent. In fact, protons from Saturn's fierce magnetosphere and ultraviolet photons from the solar wind separate molecules of nitrogen and methane. Their atoms recombine into a raft of trace constituents, including hydrogen cyanide and acetylene, many of which were detectable to the Voyagers' infrared instruments. Hydrogen cyanide plays an important role in the synthesis of amino acids and its discovery at Titan triggered early theories that the moon might harbour the building blocks for complex organic chemistry. Indeed, it may even mirror conditions on the infant Earth, as it was billions of years before life evolved here.

A Complicated Picture

During their rapid transits, the Voyagers observed cooler temperatures nearer the moon's and warmer ones in the high troposphere, a phenomenon known as 'temperature inversion'. It's driven primarily by ultraviolet sunlight and contributes to Titan's already complicated photochemical picture, which is dominated by a dense layer of hydrocarbon 'smog', 200km thick, whose particulates vary in size from 0.2µm to 1µm. Even in 1980, it was argued that these particulates could 'snow' onto Titan's surface, and so the existence of hydrocarbon lakes and seas was plausibly considered for the first time.

Eighteen hours after leaving Titan, Voyager 1 hurtled 64,200km past the sickly yellow cloud-tops of Saturn, the Solar System's most visually spectacular planet. Its intricate rings, which so puzzled Galileo in 1610, before they were correctly described and identified by Christiaan Huygens in 1655, have a radial breadth of 282,000km, equivalent to three-quarters of the distance but are believed to be no more than 1.4km thick.

Three rings, dubbed A, B and C, together with the 4,800km-wide Cassini Division, were known to astronomers long before the dawn of the Space Age. In September 1979, Pioneer 11 found the F ring, which resembled a contorted tangle of narrow strands. Moreover, its data hinted strongly at the possible existence of tiny 'moonlets', which somehow anchored, or 'shepherded', the ring material along its million-kilometre-long tracks. A year later, Voyager 1 discovered the moonlets Prometheus and Pandora, both of which straddled and possibly influenced the structure of the F ring. Unfortunately, a defective photopolarimeter meant that the probe was unable to examine them in great detail.

Still, Voyager 1 managed to locate the dusty D ring and the exceptionally slender G ring. Nine months later, Voyager 2 encountered Saturn with a fully functioning photopolarimeter and managed to resolve groups of hitherto-unseen 'ringlets', showing that very few gaps existed anywhere in the rings.

Even the notionally 'empty' Cassini Division, the broad, dark band of which separates the bright A and B rings, turned out to be populated by a vast mass of dust and rocky fragments. Radio-science measurements confirmed that the most closely spaced particles ranged in size from under 1cm to 10m or more.

The Rings' Origins

The principal constituent of the rings is water-ice. It makes up 99.9 per cent of the rings and is what makes them so dazzlingly reflective, although both Voyagers saw discoloration in places, perhaps due to the presence of impurities such as tholins or silicates. Until 1980, scientific consensus favoured gravitational forces as the driving force behind the rings' formation. Yet the Voyager probes uncovered radial features, including spokes and kinks that are inconsistent with gravitational orbital mechanics.

Voyager 1 took a sequence of images during one of Saturn's rotations that revealed the spokes' formation and dissipation lifecycles. The images showed them to be charged particles that levitated above the rings.

It had been argued that divisions within the rings were formed by the process of orbital 'resonance', whereby particles were confined to specific regions by the gravitational attraction of neighbouring shepherd moons. The discovery of Prometheus and Pandora lent credence to this idea, and particles bordering the Cassini Division are thought to be influenced by the presence of the moon Mimas.

Elsewhere, particles near the edge of the A ring are 'sharpened' by the moonlet Atlas — its astonishing equatorial ridge might represent a deposit of swept-up ring material — and by the co-orbiting moonlets Epimetheus and Janus.

Another moonlet, the walnut-shaped Pan, was found in 1990, following an analysis of old Voyager 2 images. It's thought to be responsible for 'scalloping' the edges of the 325km-wide Encke Gap in the A ring and keeping it free of particles. Still other openings in the rings — including the Cassini Division and the narrower Huygens Gap — are thought to be controlled in part by the influence of Mimas. Another gap, measuring 42km in diameter and named in honour of astronomer James Keeler, was detected by the Voyagers deep within the A ring.

Giant Storms

Unexpectedly, the composition of Saturn's atmosphere was quite distinct from Jupiter, with smaller helium abundances and a larger relative share of hydrogen — about 96 per cent, compared to the Jovian 87 per cent. Like its larger cousin, Saturn was shown to radiate more heat into space than it absorbed from incident sunlight and it rotates rapidly upon its axis, generating the polar flattening and outwardly bulging equator that's a curious characteristic of all four giants.

In a further contrast to Jupiter, Saturn is 30 per cent less massive, leading to the famous idiom that if a sufficiently large bathtub could be found, it might float on the water. Its latitudinal banding is also much less obvious. But the world whose name pays homage to the fabled father of Jupiter and Bringer of Old Age is by no means an inactive place. Half a century before the Voyagers visits, comedian and amateur astronomer Will Hay observed an elliptical white spot near Saturn's equator, one of several periodic sightings of large-scale storms at work.

When Voyager 2 flew past the planet on 25 August 1981, it revealed eastward-gusting jet-streams, which peaked at 1,800km/h — five times faster than those on Earth. Marginally greater winds were also clocked at higher latitudes. Data from both spacecraft uncovered powerful polar aurorae at latitudes above 65°N, together with ultraviolet emissions of hydrogen at mid-latitudes.

A Parting Gift

It was Pioneer 11 that first detected the unusual alignment of Saturn's magnetic field, which is tilted by less than 1° with respect to its rotational poles, while the Voyagers observed a strange 'torus' of positively charged hydrogen and oxygen ions about 400,000km above the cloud tops. The strong emissions associated with this torus were measured by the fields-and-particles instruments, revealed a million-kilometre-wide 'sheet' of plasma, perhaps supplied by atmospheric material from Saturn and Titan. The planet's magnetosphere is much smaller than the enormous cavity that encapsulates Jupiter, but was still shown to span over two million km by Voyager 1. Nine months later, when Voyager 2 arrived, solar wind pressures had heightened and markedly compressed the sunward boundary. Then, as the spacecraft departed Saturn on the outward leg of its journey, its instruments detected a sudden drop in solar wind pressure and the magnetosphere rapidly ballooned outwards in less than six hours.

It was a final parting gift. Then Voyager 2's instruments were deactivated and the spacecraft entered hibernation for its lonely, five-year trek to Uranus; the timing had almost been poetic. It seemed as if Saturn was bidding its visitors farewell, by offering up one more mystery to perplex and astound us.

Why Does Saturn Have Such Grand Rings?

For over three centuries, from the earliest observations by Galileo Galilei and Christiaan Huygens, Saturn was believed to be the only planet to have rings. More recently, its three giant cousins have revealed their own assemblages of dust and rocky grains. Despite being far less grandiose than those of Saturn, the creation and endurance of ring systems was a mystery it was hoped the Voyagers could help solve.

Two main theories took centre-stage before 1980. The first, by Edouard Roche, postulated that small moons residing at specific distances from a given planet would be torn apart by tidal forces and the debris might settle into rings. The second, by Pierre Laplace and Immanuel Kant, argued that the rings formed at the same time as Saturn, in a process similar to how the Solar System formed from a large disc.

As viewed by the Voyager probes, discrete particles in the rings were so bright and pristine — formed almost wholly water-ice, with some trace contaminants — that they seemed no older than a few hundred million years. Some particles are so small (from car-sized boulders to sand-like grains) that they would have been pulled into the atmosphere if they were much older than this. Furthermore, the Voyagers revealed exceptionally low levels of ambient radiation at Saturn, implying that the rings have thrived in a relatively benign environment.

This contributed to early theories that Jupiter, Uranus and Neptune lost their primordial gaseous discs quite early in their evolution, leaving mainly volatiles from which to assemble their far darker and less expansive ring systems. Saturn, on the other hand, cooled sufficiently early for water vapour to condense and eventually produce far more brilliant rings. During their encounters, the Voyagers also uncovered much more intricate detail, from spokes and kinks to ringlets and shepherd moons, than had been expected.

A Growing Moon Menagerie

Around a dozen moons were known to orbit Saturn before the Voyagers visited, the largest among them being the planet-sized Titan. Next largest was rocky Rhea, one-third the size at 1,530km in diameter.

It was Rhea — stripped of a 'sensible' atmosphere, globally crater-scarred and seen only from a great distance by both Voyager craft — that had endured two savage epochs of meteoroid bombardment in its youth. Those epochs are thought to have generated many craters on Saturn's other moons. Most intriguing are Tethys and Mimas, both predominantly water-ice, which showcase the biggest craters in proportion to their size ever seen. In fact, Mimas's Herschel crater (almost 10km deep and 130km across) covers a third of its diameter, so enormous that its causative impact must have almost broken the moon apart. Tethys boasts a shallower, more ancient feature, called Odysseus, which also spans a wide fraction of its terrain.

Then there's enigmatic Iapetus, which a bewildered Giovanni Cassini identified as 'two-toned' — bright on one face, dark on the other. The Voyagers revealed a meandering, 300km-wide transitional zone between the two halves, suggesting that preferential bombardment of Iapetus's leading hemisphere by darkened material could be responsible. Elsewhere, icy Enceladus reflects virtually all incident sunlight, rendering it the brightest-known natural satellite and raising early suspicions of 'cryovolcanism'. Rugged Dione was shown to possess a co-orbital companion moon, while potato-shaped Hyperion might be the remnant of an ancient collision and blob-like Phoebe could represent a seized asteroid.

With the Voyagers' close-range observations of Janus and Epimetheus, the floodgates opened. Three more moons (Atlas, Prometheus and Pandora) were found by the Voyagers and later Earth-based work on their imagery led to the detection of others, including Pan. Today, it's known that more than five dozen moons with confirmed orbits exist at Saturn, but the presence of innumerable particles within the rings — from grains to moonlets — could carry this figure into the thousands or beyond.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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Voyager: The 40-Year Space Journey Voyager: The 40-Year Space Journey
Voyager: The 40-Year Space Journey

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Voyager: The 40-Year Space Journey

In 1977, two spacecraft left Earth to explore the gas and ice giants. On the anniversary of their departure, Jenny Winder charts their journey towards the edge of the Solar System

Artist's concept of Voyager in flight

Artist's concept of Voyager in flight. By NASA/JPL [Public domain], via Wikimedia Commons

Forty years ago, in August and September 1977, NASA launched two spacecraft on an audacious mission that would eventually study all four giant outer planets and 48 of their moons, and go on to explore the outer reaches of our Solar System. Today, Voyager 1 is our most distant spacecraft, and in 2012 became the first to enter interstellar space. Voyager 2 isn't far behind; it's hoped that it too will 'go interstellar' in the next five years.

The origins of the mission hark back to 1965, when it was realised that a planetary alignment in the latter half of the 1970s would enable a spacecraft to make a complete survey of Jupiter, Saturn, Uranus, Neptune and Pluto. Such an alignment only occurs every 175 years — it was an opportunity not to be missed.

To make the most of it, NASA settled on two identical spacecraft to travel on two separate trajectories. Both would study Jupiter and Saturn. Voyager 1 would then go on to fly by Saturn's largest moon Titan. Voyager 2, meanwhile, would have the option to go to Uranus and Neptune, becoming the first spacecraft to visit either. Each planetary flyby would alter the spacecraft's flight path to deliver it onto the next planet and increase its velocity, reducing the flight time to Neptune from 30 years to just 12. Pluto was off the table; the choice was between it and Titan, and Titan was seen as a more interesting target.

Budget constraints meant the spacecraft were officially only built to last five years, with the hope that they would be able to complete the extended mission to Uranus and Neptune. They launched with 11 scientific instruments: four on Voyager 1 continue to send back data about its surroundings, while five remain operational on Voyager 2.

One of the instruments still active on both is the low-energy charged particle detector (LECP) instrument, which scans the sky through 360° every few tens of seconds measuring cosmic rays. That it continues to function is extraordinary, says its principal investigator, Dr Stamatios M Krimigis.

"The most remarkable design feature of LECP was the stepper motor," he says. "A mechanical device like this in space was frowned upon because everyone thought it could get stuck in short order. We tested the motor for about 500,000 steps, twice the expected usage and it survived. Now it's performed over seven million steps and counting."

Science data from the instruments is returned to Earth in real time via each probe's high-gain antenna. The signals are picked up by the Deep Space Network (DSN), a global spacecraft tracking system, which was also used to reprogram the spacecraft remotely on more than one occasion. Travelling too far from the Sun for solar panels to be employed, the probes rely on three radioisotope thermoelectric generators for power. These convert heat produced from the radioactive decay of plutonium into electricity.

Messages for ET

Each spacecraft also carries a message from humanity in the form of a 12-inch gold-plated copper record. The cover for the Golden Records bear diagrams explaining how to play them, showing the location of our Sun and the two lowest states of the hydrogen atom as a fundamental clock reference.

The selection of content for the record, by a committee chaired by Carl Sagan, was completed in six weeks, chosen to portray the diversity of life and culture on Earth. There are spoken greetings in 55 languages; 116 images; recordings of natural sounds; music from Bach, a Navajo Indian song, Azerbaijani folk music and Chuck Berry; and even a recording of the brainwaves of Ann Druyan, the creative director of the project.

Voyager 1 was launched two weeks after Voyager 2, but on a shorter and faster trajectory that would see it overtake its twin and reach Jupiter first. Between January and August 1979, the Voyagers studied the Jovian system. They revealed Jupiter's famous Great Red Spot to be a complex anticyclonic storm, found smaller storms throughout the planet's clouds and saw flashes of lightning in the atmosphere on the night side. Jupiter's faint, dusty rings were also discovered, along with the satellites Adrastea, Metis and Thebe. But the highlight of the Jupiter mission was the discovery of active volcanism on the moon Io. Together, the Voyagers observed the eruption of no fewer than nine volcanoes on Io. "At that time, the only known active volcanoes in the Solar System were here on Earth, and here was a moon, just a moon of Jupiter, that had 10 times more volcanic activity than here on Earth," explains Voyager project scientist Ed Stone, who has been with the mission from the start. The Voyagers also found Io was shedding a thick torus of ionised sulphur and oxygen, and revealed evidence for an ocean beneath the icy crust of Jupiter's moon Europa.

At Saturn, they studied the planet's complex rings and its atmosphere, and found aurorae at polar latitudes and aurora-like emissions of ultraviolet hydrogen at mid latitudes. They measured Titan's mass, studied its thick nitrogen atmosphere and imaged 17 of Saturn's moons, including three new discoveries: Atlas, Prometheus and Pandora.

From there the two probes parted company as Voyager 1 began its long journey out of the Solar System. Voyager 2 headed to Uranus, where it discovered 11 new moons and visited 16. It discovered the planet's magnetic field and studied the ring system. At Neptune Voyager 2 discovered storms, including the Great Dark Spot, and 1,600km/h winds — the strongest on any planet. It imaged eight of Neptune's moons, discovering five of them and saw active geysers on the largest moon, Triton.

One last glimpse

On Valentine's Day 1990, Voyager 1 took the final pictures of the mission. Turning its camera back towards the Sun, from about 6 billion km away, it took images of Neptune, Uranus, Saturn, Jupiter, Venus and — suspended in a beam of sunlight — the now famous 'Pale Blue Dot' image of Earth. Carolyn Porco planned and executed this Family Portrait alongside Carl Sagan. "As soon as I joined the Voyager imaging team in fall 1983, the idea arose in my mind to take an image of the planets, but especially Earth, as they would be seen from far away, to force that 'reckoning' that comes from seeing our cosmic place as it really is ... alone and isolated," she says.

This marked the end of the Voyagers' planetary explorations — the Grand Tour, as it's known — and the beginning of the Interstellar Mission. In 1998, Voyager 1 overtook Pioneer 10 to become the most distant spacecraft from the Sun. Voyager 2 is expected to pass Pioneer 10 by April 2019.

In December 2004, Voyager 1 crossed the termination shock, marked by a massive drop in particles detected from the Sun and a rise in cosmic ray particles. Voyager 2 followed in August 2007. Finally, on 25 August 2012, at 121 AU from the Sun, Voyager 1 officially crossed into interstellar space.

The Voyager team is still listening. "We listen every day, for four to eight hours per day, per spacecraft, and we'll continue to do that as long as they are sending us something new to learn," explains Ed Stone. From 2020, however, the remaining instruments will be switched off one by one to conserve power. It's hoped they will fly for at least 10 more years. "My goal is to have a 50th anniversary party for Voyager," says Suzanne Dodd, project manager of the Voyager Interstellar Mission.

Stone considers the Voyagers to be "our silent ambassadors". In 40,000 years, they will each pass 1.5 lightyears from stars in Andromeda and Camelopardalis. Having increased our knowledge of our solar neighborhood, the Voyagers will take the story of Earth on to other star systems.

Voyager Mission Timeline

On their long travels, the Voyagers visited four planets and imaged 48 moons. Now they are at the very edge of the Solar System.

20 August 1977
Voyager 2 launches from Cape Canaveral at 14:29 UT atop a Titan IIIE-Centaur launch vehicle

5 September 1977
Voyager 1 launches at 12:56 UT from Cape Canaveral also atop a Titan IIIE-Centaur

10 December 1977
Voyager 2 enters the asteroid belt, swiftly followed by Voyager 1

19 December 1977
Voyager 1 overtakes its twin, placing it on course to reach Jupiter first

8 September 1978
Voyager 1 exits the asteroid belt and continues on to Jupiter

21 October 1978
On a slower trajectory, Voyager 2 finally exits the asteroid belt

5 March 1979
Voyager 1 makes its closest approach to Jupiter

9 July 1979
Voyager 2 makes its closest approach to Jupiter

12 November 1980
Voyager 1 flies by Titan and Saturn, then begins its journey out of the Solar System

25 August 1981
Voyager 2 flies by Saturn but remains within the plane of the planets, bound for Uranus

24 January 1986
Voyager 2 has the first-ever encounter with Uranus, revealing a bland visible surface

25 August 1989
Voyager 2 is the first probe to observe Neptune, a stormier planet than its neighbor

14 February 1990
Voyager 1 takes the Pale Blue Dot image of Earth from 6 billion km away

17 February 1998
Voyager 1 becomes the most distant human-made object in space

17 December 2004
Voyager 1 passes the termination shock and enters the heliosheath

30 August 2007
Voyager 2 passes the termination shock and enters the heliosheath

25 August 2012
Voyager 1 crosses the heliopause and enters interstellar space

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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The Unknown Realm of the Ice Giants The Unknown Realm of the Ice Giants
The Unknown Realm of the Ice Giants

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The Unknown Realm of the Ice Giants: Uncharted Territory — Uranus & Neptune

In January 1986 and August 1989, Voyager 2 flew past the outer giants Uranus and Neptune — becoming the first spacecraft to visit either. In its brief visits, these cold worlds almost beyond the reach of the Sun's warmth were revealed to be every bit as mysterious as their closer cousins.

Uranus as seen by NASA's Voyager 2

Uranus as seen by NASA's Voyager 2. By NASA (http://photojournal.jpl.nasa.gov/catalog/PIA18182) [Public domain], via Wikimedia Commons

Perhaps the toughest kind of exploration is studying a pair of planets about which virtually nothing is known with certainty. In February 1984, several dozen scientists gathered in Pasadena, California, to consider the scant level of knowledge about Uranus and Neptune. These two giants, which reside on the fringe of our planetary system, had only been discovered in the preceding two centuries. And as Voyager 2 journeyed towards them for humanity's first-ever visits, neither had revealed itself as much more than a fuzzy blob in an ocean of emptiness.

Worth a visit

The desire to travel to Uranus and Neptune originated with NASA's Grand Tour programme, but a subsequent rescoping of the mission led to a revised focus on Jupiter and Saturn. Nevertheless, in 1976 NASA approved an extension to Uranus on the condition that all primary objectives were met. A modified infrared detector was built to achieve the necessary resolution at Uranian distance — 2.6 billion km from Earth — but when the Uranus flyby formally began it did so with a greatly reduced budget and a leaner workforce.

By that time Uranus was known to possess five moons, named after characters from the works of William Shakespeare and Alexander Pope. The first pair, Titania and Oberon, were found in 1787 by Uranus's own discoverer, William Herschel, with Ariel and Umbriel observed by William Lassell in 1851 and tiny Miranda identified by Gerard Kuiper in 1948. Some 1.6 billion km beyond Uranus, Neptune was attended by Triton and Nereid, fittingly named after classical deities of the sea. All were barely detectable with Earth-based instruments before the Voyager 2 probe arrived.

Following Uranus's discovery in 1781 and the finding of Neptune thanks to the mathematical predictions and telescopic observations of Johann Galle, Urbain Le Verrier and John Couch Adams in 1846, there existed only the most general and sweeping awareness of either planet. They were known to be near-twins in size, with equatorial diameters around 50,000km, four times bigger than Earth and over 15 times more massive. The probe confirmed hydrogen and helium as their predominant constituents. Uranus's plain aquamarine colour and the richer, sky-blue façade of Neptune also betrayed the presence of ammonia, methane and hydrogen sulphide.

Data gathering

Travelling at 64,000km/h, Voyager 2 had only six hours on 24 January 1986 to make its close-range observations of Uranus. But to maximise the scientific yield of its flyby, the probe took measurements of the planet continually for 16 weeks from November 1985 until February 1986. A similar campaign was adopted at Neptune from June to October 1989. "We had a prediction of where the spacecraft would be at each point in time," recalled Voyager imaging team member Andrew Ingersoll. "We told the engineers what latitude and longitude we wanted to look at and they told the camera to take a picture. These commands had to be worked out and radioed to the probe weeks in advance."

Due to Uranus's 98° axial tilt, Voyager 2 approached the planet's sunward-facing south pole and generated time-lapse movies to track cloud movements and wind speeds. Unlike on Jupiter and Saturn, there was little evidence of storms or latitudinal banding, which led the imaging team to wryly dub themselves 'the imagining team'. However, infrared data revealed clouds beneath a high-altitude layer of hydrocarbons and the probe's radio-science and ultraviolet instruments revealed uniform temperatures throughout the atmosphere of around -216°C.

Theories abounded that this atmosphere might extend more than 3,000km beneath the cloud tops, perhaps terminating in a slushy ocean of water, ammonia and methane, girdling an Earth-sized rocky core. A similar situation is also thought to exist at Neptune. Voyager 2 was unable to prove the existence of such oceans, but did detect radio signals induced by interactions between the solar wind and electrons in the planets' magnetic fields. This enabled its magnetometer to measure Uranus's day at 17.25 hours and Neptune's day at 16.1 hours, which in turn helped provide wind-speed estimates.

The dark of the moons

To great surprise, Uranus's magnetic field extended only 600,000km sunward, but wound backwards, like a giant corkscrew, 10 million km beyond the planet. Ultraviolet observations of polar aurorae showed that the field was tilted at 59° to Uranus's rotational axis — a curiosity that, on Earth, would be equivalent to having our north magnetic pole in the Florida Keys — and bore a powerful sting in the guise of trapped, high-energy radiation. This clearly manifested itself on the surfaces of Uranus's moons.

All five moons appeared intrinsically dark, suggesting that radiation had broken down any methane on their surfaces within a few tens of millions of years, darkening them and leaving a thick, charcoal-like dusting. Umbriel is by far the darkest, although it does exhibit a few splotches of bright material, including an enigmatic 'Cheerio' in the crater Wunda at its equator. As for its siblings, Titania — the largest, at 1,580km across — is marred by huge faults and winding canyons, pointing to a violent tectonic past. Oberon revealed bright and dark regions, not unlike our Moon, indicating meteoroid bombardment and perhaps the volcanic extrusion of subsurface material.

But it was Miranda and Ariel to which Voyager 2 devoted the most attention. The latter is the brightest Uranian moon, with an ancient and heavily cratered terrain that features rolling plains, parallel ridges and troughs lying tens of kilometres apart. Miranda, less than 500km in diameter, was the most closely inspected, principally due to the flyby geometry needed by Voyager 2 to reach Neptune.

It revealed unmistakable evidence of billions of years of impacts, which tore Miranda apart, then hammered it back together, gouging out 20km-deep canyons, at least three enormous, oval-shaped 'coronae' and broad terraces of old and young, bright and dark, lightly and heavily cratered terrain. One area, the 200km-wide Inverness Corona, showed a bright chevron-like feature between dark layers, possibly a result of reaggregated bits of Miranda's original crust, poking out from the present surface.

New moons

Voyager 2 also found 10 new moons, ranging from 160km-wide Puck to diminutive Cordelia, about an eighth as large. A small subset that share similar orbits, surface colouration and generally elongated shapes was classified as the 'Portia Group' (named for its biggest member). Another object was photographed by the probe, but went unrecognised as a moon until 1999. It was fittingly named 'Perdita', the Latin word for lost.

Something that had already been seen at Saturn was the pivotal role tiny 'shepherd' moons play in anchoring ring material. Several narrow rings had been detected around Uranus by ground-based observers in the 1970s, but Voyager 2 uncovered another pair. The probe revealed the new pair to be relatively insubstantial, although the brighter 'Epsilon ring' achieved a maximum extent of 96km.

Up to 18 shepherd moons were predicted to exist at Uranus, but only two — Cordelia and Ophelia — were detected, lying astride and 'binding' the inner and outer edges of the Epsilon ring. The general darkness of the rings underscores their extreme youth, for they are probably no more than 600 million years old. Data from Voyager 2's photopolarimeter and other instruments revealed them to be so sharp that the Epsilon component can't be greater than 150m thick.

Rings were also eagerly anticipated at Neptune, with ground-based studies between 1968 and the early 1980s suggesting that incomplete 'arcs' might run part-way around the planet. Numerous theories postulated that the arcs were held in place by tiny shepherd moons or maybe new rings were in the process of forming. With just two weeks to go until Voyager 2's arrival, their true nature was revealed. A pair of incomplete arcs did appear to exist, with three shepherd moons (Galatea, Larissa and Despina) interacting with them.

Building rings

As the probe drew nearer, it became apparent that more rings extended around the planet. Their uneven 'clumpiness' and irregularly distributed particles offered an early explanation for why arcs had been suspected for so long. Indeed, Neptune's outermost 'Adams' ring revealed several clods of material, up to 50km wide. It was argued that debris from ancient moons could have contributed to this unequal distribution of mass and a pair of tiny moons, Thalassa and Naiad, could themselves someday be torn apart and incorporated into the system.

Voyager 2 confirmed the existence of six new moons at Neptune, including potato-shaped and heavily cratered Proteus, which is thought to be almost big enough for gravity to pull it into a spherical shape. Eccentric-orbiting Nereid, discovered by Gerard Kuiper in 1949, was also seen by the probe, but at a distance of 4.7 million km it was still too far away to resolve any surface detail, much less measure its rotational characteristics.

Before it found any rings, it was hoped that Voyager 2 would fly within 10,000km of the planet's largest moon, Triton, which ground-based observations had shown to possess nitrogen ices on its surface. To avoid the risk of colliding with ring particles, the probe's trajectory was altered to carry it 4,950km over Neptune's north pole — the closest planetary encounter achieved by either Voyager craft — on 25 August 1989. It then plunged south, passing within 39,800km of Triton, five hours later.

Circling Neptune in a highly inclined 'retrograde' orbit, the moon proved smaller than predicted, at just 2,700km across, and a stellar occultation allowed Voyager 2 to measure its 800km-deep atmosphere, all the way down to its surface, the coldest known in the Solar System at a frigid -236°C. In fact, Triton's tenuous mix of gases and particulates is virtually a vacuum, barely capable of supporting thin nitrogen-ice clouds and haze at an altitude of 13km.

Voyager 2 strongly hinted that these constituents originated from the evaporation of surface ices, with winds transporting dust particles up to 50km across its terrain. Triton is the most spectroscopically diverse object in the Solar System, reflecting over 85 per cent of incident sunlight — eight times more than our Moon — and this extreme brightness was a key reason why such a tiny, distant body was found telescopically by William Lassell in October 1846, just weeks after Neptune itself.

Freeze-thaw effect

The probe imaged a third of Triton's surface, uncovering a greenish landscape, nicknamed 'cantaloupe', due to its similarity to the scaly skinned melon. It was crisscrossed with circular depressions, each around 25km wide, and long, interconnecting ridges were thought to be the result of epochs of melting and refreezing. This reinforced the notion of Triton as a captured Kuiper Belt object and that the tidal heating from Neptune's gravity had left its interior fluid for a billion years, underpinning these complex internal processes.

Voyager 2 also revealed a pinkish southern polar cap, abutted by a blue-tinged crustal region, indicative of the presence of methane, nitrogen and water ices. And it was from within the polar caps that a moderate greenhouse effect could have been nurtured, forcing exotic ices to 'de-gas' and build pressure, before prompting one of the most surprising discoveries at Triton: erupting geysers.

In August 1989, only Earth and Jupiter's moon, Io, were known to harbour active volcanism, but dark streaks across Triton's southern polar cap indicated that such phenomena were commonplace, even in this far-flung corner of the Solar System. One geyser was observed to hurl carbonaceous material to an altitude of several thousand metres, while other measurements allowed local wind speeds to be clocked at 54km/h, as strong as a moderate gale on Earth.

Providing a backdrop to these discoveries was magnificent Neptune itself, whose outward similarity to Uranus belied a far more active world. Despite its greater distance from the Sun, infrared data showed it to radiate 2.6 times as much heat from incident sunlight as Uranus. And although the near-twins are thought to have similar compositions, Neptune is marginally more massive, which influences its magnetic field and internal heat. "Wow," exulted one planetary scientist, breathlessly, as Voyager 2 became the only spacecraft in history to visit four planets. "What a way to leave the Solar System!"

Beefing up the Voyagers from the ground

Orbiting billions of kilometers beyond Saturn, the outer giants Uranus and Neptune inhabit a gloomy region of the Solar System, requiring Voyager 2 to examine worlds where high noon is dimmer than dusk on Earth. One scientist likened the problem to photographing a pile of charcoal briquettes lying at the foot of a Christmas tree, lit by a single-Watt bulb.

Stability was crucial, but even turning its tape recorder on and off was enough to induce a disruptive 'nodding' effect in Voyager 2. Its gyroscopes could keep the instruments reasonably steady, but engineers had to halve the duration of thruster firings to allow the probe to settle after manoeuvres. At Neptune, longer exposures of 96 seconds and thruster firings under four milliseconds became necessary. Image motion compensation allowed Voyager 2 to resolve finer detail, but at the expense of picking out irritating optical flaws, including dust on its lenses.

Back on Earth, the three tracking stations that make up NASA's Deep Space Network (located in Canberra, Australia, the remote foothills west of Madrid in Spain and in California's Mojave Desert) received a $100 million facelift to boost Voyager 2's ever-weakening signal, which by January 1986 was a billion times fainter than a watch battery. All three stations had their 64m antennas augmented for Uranus, electronically synchronising them to strengthen the signal. Further upgrades to 70m were implemented for Neptune and two additional tracking stations in Japan and New Mexico were called into duty.

Due to the position of Uranus in Earth's skies in the winter of 1985-1986, Canberra was the main tracking station, following Voyager 2 for 12 hours per day and allowing a 21.6kbps downlink rate. In support, a 400km microwave connection was established with the Parkes radio telescope in New South Wales, bolstering it by 25 per cent and allowing up to 50 extra photographs to be returned every day.

The Bullseye Planet

Uranus is unique among the planets in our Solar System thanks to its extraordinary rotational tilt of 98° — Uranus presents itself to observers as a world tipped on its side. Its poles lie where its equator should be and receive a correspondingly higher level of incident sunlight. Situated 2.8 billion km from the Sun, Uranus circles its parent star every 84 years, with each pole rhythmically illuminated, before being plunged into frigid darkness, every four decades.

When Voyager 2 viewed the planet only the southern pole was in direct sunlight. Its five main moons orbit their giant host within its equatorial plane, placing their southern halves at the height of Uranian summer in January 1986 and casting their northern extremities into a 21-year-long winter season.

How Uranus's axial tilt came about remains a mystery, although a collision with an Earth-sized impactor has been proposed. The fact that the moons circle within its equatorial plane implies that they formed much later from debris placed into orbit by this impact. Moreover, Uranus radiates hardly any heat into space — its temperatures dip as low as -224°C, giving it the coldest planetary atmosphere in the Solar System — and it's possible that whatever hit the planet caused it to expel much of its primordial heat.

A World Of Wild Weather

Four-and-a-half billion kilometres from its parent star, recipient of half as much sunlight as gloomy Uranus and with temperatures as low as -218°C, Neptune should be an inactive world. Yet Voyager 2 revealed it to be surprisingly energetic, with the oval-shaped Great Dark Spot observed at a latitude of 22°S. This counter-clockwise-rotating vortex bore many uncanny parallels with Jupiter's Great Red Spot, in terms of relative size, motion and position within the atmosphere.

As the probe drew closer, a second, smaller dark spot was found, together with a chevron-shaped, westward-moving cloud feature, whose rapid 16-hour transit around Neptune's atmosphere generated the nickname of 'Scooter'. The Great Dark Spot, in keeping with its name, was 10 per cent darker than its surroundings and hustled northwards through the atmosphere at 1,100km/h. At its edge was a hovering, shape-shifting 'bright companion' cloud. The spot lay 50km below Neptune's main cloud deck, with the companion at a slightly higher altitude, creating analogies with lenticular cloud formations on Earth.

Elsewhere in the sky-blue atmosphere were cirrus streaks of methane-ice, which cast shadows, tens of kilometres long, on Neptune's cloud deck at low northern latitudes. How such wild weather can manifest itself on such a cold planet must be related to its dense interior and the fact that it emits 2.6 times as much heat as it receives from incident sunlight. It has been suggested that temperature differences between Neptune's internal heat and its cold atmosphere could trigger instabilities and induce large-scale meteorological phenomena.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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Missions of the Future Missions of the Future
Missions of the Future

Orion is proud to partner with BBC Sky at Night Magazine, the UK's biggest selling astronomy periodical, to bring you this article as part of an ongoing series to provide valuable content to our customers. Check back each month for exciting articles from renowned amateur astronomers, practical observing tutorials, and much more!

Missions of the Future

With a fleet of probes being readied for flight over the next few years, Elizabeth Pearson looks at the destinations these missions will be heading to throughout our Solar System, as well as what they hope to uncover

Space probe and Jupiter

Image from Pixabay courtesy of Andrew-Art, Space probe and Jupiter

Mercury

Only two spacecraft have ever been sent to the innermost planet of our Solar System, but that number is set to double. Two probes will fly to Mercury together as part of the BepiColombo mission, due for launch in 2018: ESA's Mercury Planet Orbiter and JAXA's Mercury Magnetospheric Orbiter. These two spacecraft will work together to provide a complete study of the planet's geology, composition, structure and interior when it arrives at the planet in 2024. The aim is to understand Mercury's place in our Solar System's creation and history. One of the greatest mysteries the two the probes will address is that of planet's magnetic field, first detected by Mariner 10 in 1974.

Mercury should be too small to host a molten core, thought to drive the magnetic fields of other planets; uncovering the interior of this world will help clarify which planets are capable of hosting a magnetosphere, both in this planetary system and beyond.

The Moon

Since the early days of the Space Race, reaching the Moon has been a symbol of a country's prowess as a spacefaring nation. But with NASA's eyes on Mars and Russia's lunar exploration programme suspended until 2025, it's time for new players in the space game to join the ranks of lunar explorers.

Both China and India have already conducted lunar missions and both are planning on building on their successes. Chang'e 5 will continue the China National Space Administration's (CNSA's) robotic exploration of the Moon in 2017, and return up to 2kg of material to the Earth — the first fresh lunar samples since 1976.

Set to launch in 2019, another Chinese mission, Chang'e 4, was initially intended as a back up to Chang'e 3. Following that mission's success it was reconfigured to land on the far side of the Moon, an area that has never been visited. The Indian Space Research Organisation (ISRO) is also hoping to cement its spacefaring credentials with the Chandrayaan-2 mission in 2018. The mission will land a rover on the lunar surface — the nation's first attempt touch down on another world.

But the days of space agencies holding sole claim to the Moon could be about to change, as a fleet of private companies are in the final leg of their own race to the lunar surface. The Google Lunar X Prize challenged private groups to land a rover on the Moon by the end of 2017. Three companies have arranged launch contracts so far. After many years of silence, the lunar surface is about to get a lot busier.

Mars

The Red Planet has had its fair share of visitors in recent years, a trend that will continue for the next decade as several new missions head for Mars.

NASA will continue its long legacy of Martian exploration with the InSight (Interior Exploration using the Seismic Investigations, Geodesy and Heat Transport)mission due for launch in 2018. It is a stationary lander that will measure the planet's seismological and thermal activity to work out what's going on under Mars's crust.

In 2020, not one but two new rovers will launch for the Red Planet — NASA's Mars 2020 rover and the second phase of ESA's ExoMars mission, which began in 2016 with the Trace Gas Orbiter. Both of these missions will look for signs of life, past and present, and try to determine if Mars was ever habitable.

But the time of robotic dominion over Mars could soon be at an end, as several key players are beginning to make real moves towards landing humans on the Martian surface. Both Chinese and US officials have stated a desire to start crewed missions to Mars over the next few decades. However, it might not be a government agency to put the first person on Mars, but a commercial one. SpaceX has always been vocal about its intention not only to launch a manned Mars mission, but also to set up a permanent base there. As a first step the company plan to fly and land a modified version of the Dragon module, currently used to send supplies to the International Space Station. This robotic mission, slated for 2018, could be a first step towards the century long journey of making humankind a multi-planet species.

Asteroids

The rubble of our Solar System's formation survives all around in the form of asteroids. Though mostly found in the asteroid belt, there are hundreds of these space rocks that regularly cross Earth's orbit, making them a tempting target for study.

Two missions to visit these cosmic wanderers are already underway, and both hope to return samples to Earth. JAXA's Hayabusa-2 spacecraft launched in 2014, bound for asteroid 162173 Ryugu. Once the probe arrives in 2018 it will obtain three samples, one of which will be excavated using an explosive charge, returning them in 2020. Its launch was followed by NASA's OSIRIS-REX, which set off for asteroid 101955 Bennu in 2016. Once there it will use gas jets to blast dust and rock off the surface before returning them home in 2023.

But robotic missions can only do so much, and NASA is currently planning an audacious mission to send humans to one of our rocky neighbours. The Asteroid Redirect Mission (ARM) will send a robotic probe to a near-Earth asteroid in the 2020s, retrieving a boulder weighing several tons from its surface and transferring it to Earth orbit.

From there, NASA will stage a series of manned missions to the boulder using the Orion crew module, which itself is still in development and hopes to fly in 2021.

This would be the first time such studies have been performed on the primordial bodies in space, rather than being returned to Earth. The mission would also provide a test bed for technologies that could one day take humanity deeper into the Solar System. Asteroids may prove a vital part of such endeavors, as mining them could provide raw materials for building spacecraft in orbit, as well as water. This could can be split into hydrogen and oxygen, and used in rocket fuel.

The Outer Solar System

The Solar System beyond the asteroid belt has remained relatively unexplored since the Voyager probes passed through three decades ago. But the giants of the outer Solar System will soon be giving up their secrets, as several missions to visit this mysterious region are planned. Juno is in the process of mapping out the largest of the gas giants, Jupiter, but it is this planet's companions that will be the next targets.

ESA's first mission to Jupiter, the Jupiter Icy Moons Explorer (JUICE) is currently being designed to make detailed observations of not only the planet, but three of the Galilean moons — Ganymede, Callisto and Europa. All of these worlds could potentially host liquid water oceans beneath an icy crust, making them the likeliest places to discover life beyond Earth. Aiming for a 2022 launch date, JUICE will find out not only if such oceans exist, but how they came to be and how likely it is that such moons are habitable.

Meanwhile NASA is planning a mission for the late 2020s that will perform multiple flybys of Europa, to help us understand its geology. Still in the concept phase, there is the potential for a lander, but it would not be capable of tunnelling through the several kilometers of ice to reach the subsurface ocean. Luckily, the Hubble Space Telescope has spotted jets of water shooting hundreds of kilometers above the moon's crust. If the main probe could fly through one of these, it could take a sample that originated deep within the moon.

NASA plans to venture even further into the outer reaches with its following mission — to Uranus. Currently under consultation, the spacecraft would orbit around the planet, which hasn't been visited in over three decades. Back then, Voyager 2 gave us only a handful of images of a seemingly placid world. Though it's unlikely we will see such a mission before the 2030s, it's worth the wait to see what Uranus hides beneath this calm exterior.

Beyond the Solar System

Though much of the focus of future space missions is on the planets around us, there is a much wider Universe waiting to be explored.

Exoplanets are one of the hottest research topics at the moment and there are several new observatories on the way. NASA's Transiting Exoplanet Survey Satellite (TESS) has already been built, ready for launch later in 2017. It will search the whole sky for exoplanets, but its main aim is to track down Earth-sized planets around nearby bright stars. Once found, those similar to our own world would be prime targets for follow up study by the Characterising Exoplanet Satellite (CHEOPS), which ESA is building for a 2018 launch. Looking at already known exoplanets, CHEOPS will be able to determine their precise orbital properties and radii.

The next goal will be to understand the atmosphere that surrounds these worlds. The UK-built Twinkle satellite, which has just finished its design phase and is planned to launch in 2019. Its aim is to capture the 0.01 per cent of starlight that shines through an exoplanet's atmosphere, which can then be untangled to reveal what chemicals compose it. Perhaps the most anticipated tool in the exploration of exoplanets, however, is the James Webb Space Telescope. From 2018 onwards, this amazing infrared telescope could be used to look at these distant planetary atmospheres, and will be able to do much more besides. Touted as the Hubble Space Telescope's successor, the JWST will be able to study everything from the origin of the Solar System to the first light that ever shone in the Universe.

ESA plans to extend its own cosmic vision with the construction of two deep space observatories — Euclid in 2020 and Athena in 2028. These will help to identify the structure and geometry that govern our Universe, and to unlock the answers of how the cosmos we know came to be.

Future missions at a glance

There are dozens of missions set to take flight in the next decade, but where will they be headed?

2017:

Chang'e 5
Type: Lunar lander
Goal: Sample return

TESS
Type: Satellite
Goal: Exoplanet search

Google Lunar X Prize candidates
Type: Lunar lander and rover
Goal: Dependant on winner

2018:

BepiColombo
Type: Mercury orbiter
Goal: Geological and magnetospheric survey

Hayabusa-2
Type: Orbiter
Goal: Asteroid sample-return mission

OSIRIS-REX
Type: Orbiter
Goal: Asteroid sample-return mission

CHEOPS
Type: Satellite
Goal: Exoplanet measurement

InSight
Type: Mars lander
Goal: Seismic and geological survey

James Webb Space Telescope (JWST)
Type: Space observatory
Goal: Infrared imaging

Red Dragon
Type: Spacecraft
Goal: Test flight to Mars

Chandrayaan-2
Type: Lunar orbiter, lander and rover
Goal: Mineralogical and geological survey

2019:

Chang'e 4
Type: Lunar lander and rover
Goal: Mineralogical and geological survey

2020:

Mars 2020
Type: Mars rover
Goal: Habitability search

ExoMars 2020
Type: Mars rover
Goal: Habitability search

Euclid
Type: Space observatory
Goal: Observing the early Universe

2021:

Juice
Type: Orbiter
Goal: Observe Gallilean satellites at Jupiter

Plato
Type: Satellite
Goal: Exoplanet characterisation

Europa Clipper
Type: Orbiter
Goal: Habitability study of Europa

Athena
Type: Space observatory
Goal: X-ray imaging

Neptune Orbiter Mission
Type: Orbiter
Goal: Planetary observation

Arm
Type: Crewed
Goal: Redirect and survey asteroid

ABOUT THE WRITER
Dr. Elizabeth Pearson is BBC Sky at Night Magazine's news editor. She has a PhD in extragalactic astronomy.

Copyright © Immediate Media. All rights reserved. No part of this article may be reproduced or transmitted in any form or by any means, electronic or mechanical without permission from the publisher.

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