Posted on by Paul Scott Anderson

When Stars Play Planetary Pinball

Artist's conception of a binary star sunset seen from the planet Kepler-16b. Credit: NASA/Ames Research Center/Kepler Mission

[/caption]

Many of us remember playing pinball at the local arcade while growing up; it turns out that some stars like it as well. Binary stars can play tug-of-war with an unfortunate planet, flinging it into a wide orbit that allows it to be captured by first one star and then the other, in effect “bouncing” it between them before it is eventually flung out into deep space.

The new paper, by Nick Moeckel and Dimitri Veras of the University of Cambridge, will be published in a future issue of Monthly Notices of the Royal Astronomical Society.

The gravitational pull of large gas giant planets can affect the orbits of smaller planets; that scenario is thought to have occurred in our own solar system. In some cases, the smaller planet may be flung into a much wider orbit, perhaps even 100 times wider than Pluto’s. In the case of single stars, that’s normally how it ends. In a binary star system, however, the two stars may play a game of “cosmic pinball” with the poor planet first.

Moeckel and Dimitri conducted simulations of binary star systems, with two sun-like stars orbiting each other at distances between 250 and 1,000 times the distance of the Earth from the Sun. Each star had its own set of planets. The planetary systems would often become unstable, resulting in one of the planets being flung out, where it could be subsequently captured by the other star’s gravity. Since the new orbit around the second star would also tend to be quite wide, the planet would be vulnerable to recapture again by the first star. This could continue for a long time, and the simulations indicated that more than half of all planets initially ejected would get caught in this game of “cosmic pinball.”

In the end, some planets would settle back into an orbit around one of the stars, but the majority would escape both stars altogether, finally being flung out into deep space forever.

According to Moeckel, “Once a planet starts transitioning back and forth, it’s almost certainly at the beginning of a trip that will end in deep space.”

We are fortunate to live in a solar system where our planet is in a nice, stable orbit. For others out there who may not be so lucky, it would be like living through a disaster movie played out over eons.

The paper is available here.

Posted on by Paul Scott Anderson

600 Million Year Drought Makes Life on Surface of Mars Unlikely

View of Mars' surface near the north pole from the Phoenix lander. Polygon shapes can be seen in the soil. Credit: NASA/JPL-Calech/University of Arizona

[/caption]

Mars is often referred to as a desert world, and for good reason – its surface is barren, dry and cold. While water was abundant in the distant past, it has long since disappeared from the surface, although ice, snow, frost and fog are still common. Other than liquid brines possibly trickling at times, all of Mars’ remaining water is now frozen in permafrost and in the polar ice caps. It has long been thought that the harsh conditions would make current life unlikely at best, and now a new study reaffirms that view.

The results come from continued analysis of the data from the Phoenix lander mission, which landed in the arctic region near the north pole of Mars in 2008. They suggest that Mars has experienced a prolonged drought for at least the past 600 million years.

According to Dr. Tom Pike from Imperial College London, “We found that even though there is an abundance of ice, Mars has been experiencing a super-drought that may well have lasted hundreds of millions of years. We think the Mars we know today contrasts sharply with its earlier history, which had warmer and wetter periods and which may have been more suited to life. Future NASA and ESA missions that are planned for Mars will have to dig deeper to search for evidence of life, which may still be taking refuge underground.”

The team reached their conclusions by studying tiny microscopic particles in the soil samples dug up by Phoenix, which had been photographed by the lander’s atomic-force microscope. 3-D images were produced of particles as small as 100 microns across. They were searching specifically for clay mineral particles, which form in liquid water. The amount found in the soil would be a clue as to how long the soil had been in contact with water. It was determined that less than 0.1 percent of the soil samples contained clay particles, pointing to a long, arid history in this area of Mars.

Since the soil type on Mars appears to be fairly uniform across the planet, the study suggests that these conditions have been widespread on the planet, and not just where Phoenix landed. It’s worth keeping in mind though that soil particles and dust on Mars can be distributed widely by sandstorms and dust devils (and some sandstorms on Mars can be planet-wide in size). The study also implies that Mars’ soil may have only been exposed to liquid water for about 5,000 years, although some other studies would tend to disagree with that assessment.

It should also be noted that more significant clay deposits have been found elsewhere on Mars, including the exact spot where the Opportunity rover is right now; these richer deposits would seem to suggest a different history in different regions. Because of this, and for the other reasons cited above, it may be premature then to extrapolate the Phoenix results to the entire planet, similar soil types notwithstanding. While this study is important, more definitive results might be obtained when physical soil samples can actually be brought back to Earth for analysis, from multiple locations. More sophisticated rovers and landers like the Curiosity rover currently en route to Mars, will also be able to conduct more in-depth analysis in situ.

The Phoenix soil samples were also compared to soil samples from the Moon – the distribution of particle sizes was similar between the two, indicating that they formed in a similar manner. Rocks on Mars are weathered down by wind and meteorites, while on the airless Moon, only meteorite impacts are responsible. On Earth of course, such weathering is caused primarily by water and wind.

As for the life question, any kind of surface dwelling organisms would have to be extremely resilient, much like extremophiles on Earth. It should be kept in mind, however, that these results apply to surface conditions; it is still thought possible that any early life on the planet could have continued to thrive underground, protected from the intense ultraviolet light from the Sun, and where some liquid water could still exist today.

Given Mars’ much wetter early history, the search for evidence of past or present life will continue, but we may have to dig deep to find it.

Posted on by Paul Scott Anderson

New Study Shows How Trace Elements Affect Stars’ Habitable Zones

Comparison of the habitable zone around the Sun in our solar system and around the star Gliese 581. Credit: ESO

[/caption]

Habitable zones are the regions around stars, including our own Sun, where conditions are the most favourable for the development of life on any rocky planets that happen to orbit within them. Generally, they are regions where temperatures allow for liquid water to exist on the surface of these planets and are ideal for “life as we know it.” Specific conditions, due to the kind of atmosphere, geological conditions, etc. must also be taken into consideration, on a case-by-case basis.

Now, by examining trace elements in the host stars, researchers have found clues as to how the habitable zones evolve, and how those elements also influence them. To determine what elements are in a star, scientists study the wavelengths of its light. These trace elements are heavier than the hydrogen and helium gases which the star is primarily composed of. Variations in the composition of these stars are now thought to affect the habitable zones around them.

The study was led by Patrick Young, a theoretical astrophysicist and astrobiologist at Arizona State University. Young and his team presented their findings on January 11, 2012 at the annual meeting of the American Astronomical Society in Austin, Texas. He and his colleagues have examined more than a hundred dwarf stars so far.

An abundance of these elements can affect how opaque a star’s plasma is. Calcium, sodium, magnesium, aluminum and silicon have been found to also have small but significant effects on a star’s evolution – higher levels tended to result in cooler, redder stars. As Young explains, “The persistence of stars as stable objects relies on the heating of plasma in the star by nuclear fusion to produce pressure that counteracts the inward force of gravity. A higher opacity traps the energy of fusion more efficiently and results in a larger radius, cooler star. More efficient use of energy also means that nuclear burning can proceed more slowly, resulting in a longer lifetime for the star.”

The lifetime of a star’s habitable zone can also be influenced by another element – oxygen. Young continues: “The habitable lifetime of an orbit the size of Earth’s around a one-solar-mass star is only 3.5 billion years for oxygen-depleted compositions but 8.5 billion years for oxygen-rich stars. For comparison, we expect the Earth to remain habitable for another billion years or so, for about 5.5 billion years total, before the Sun becomes too luminous. Complex life on Earth arose some 3.9 billion years after its formation, so if Earth is at all representative, low-oxygen stars are perhaps less than ideal targets.”

As well as the habitable zone, the composition of a star can determine the eventual composition of any planets that form. The carbon-oxygen and magnesium-silicon ratios of stars can affect whether a planet will have magnesium or silicon-loaded clay minerals such as magnesium silicate (MgSiO3), silicon dioxide (SiO2), magnesium orthosilicate (Mg2SiO4), and magnesium oxide (MgO). A star’s composition can also play a role in whether a rocky planet might have carbon-based rock instead of silicon-based rock like our planet. Even the interior of planets could be affected, as radiocative elements would determine whether a planet has a molten core or a solid one. Plate tectonics, thought to be important for the evolution of life on Earth, depend on a molten interior.

Young and his team are now looking at 600 stars, ones that are already being targeted in exoplanet searches. They plan to produce a list of the 100 best stars which could have potentially habitable planets.

Posted on by Paul Scott Anderson

How Plants May Have Helped Create Earth’s Unique Landscapes

Credit: Wikimedia Commons

[/caption]

According to conventional thinking, plant life first took hold on Earth after oceans and rivers formed; the soil produced by liquid water breaking down bare rock provided an ideal medium for plants to grow in. It certainly sounds logical, but a new study is challenging that view – the theory is that vascular plants, those containing a transport system for water and nutrients, actually created a cycle of glaciation and melting, conditions which led to the formation of rivers and mud which allowed forests and farmland to later develop. In short, they helped actually create the landscapes we see today.

The evidence was just published in two articles in a special edition of Nature Geoscience.

In the first article, analysis of the data proposes that vascular plants began to absorb the carbon dioxide in the atmosphere about 450 million years ago. This led to a cooling of temperatures on a global scale, resulting in widespread glaciation. As the glaciers later started to melt, they ground up the Earth’s surface, forming the kind of soils we see today.

The second article goes further, stating that today’s rivers were also created by vascular plants – the vegetation broke the rocks down into mud and minerals and then also held the mud in place. This caused river banks to start forming, acting as channels for water, which up until then had tended to flow over the surface much more randomly. As the water was channeled into more specific routes, rivers formed. This led to periodic flooding; sediments were deposited over large areas which created rich soil. As trees were able to take root in this new soil, debris from the trees fell into the rivers, creating logjams. This had the effect of creating new rivers and causing more flooding. These larger fertile areas were then able to support the growth of larger lush forests and farmland.

According to Martin Gibling, a professor of Earth science at Dalhousie University, “Sedimentary rocks, before plants, contained almost no mud. But after plants developed, the mud content increased dramatically. Muddy landscapes expanded greatly. A new kind of eco-space was created that wasn’t there before.”

The new theory also leads to the possibility that any exoplanets that happen to have vegetation would look different from Earth; varying circumstances would create a surface unique to each world. Any truly Earth-like exoplanets might be very similar in general, but the way that their surfaces have been modified might be rather different.

It’s an interesting scenario, but it also raises other questions. What about the ancient river channels on Mars? Some appear to have been formed by brief catastrophic floods, but others seem more similar to long-lived rivers here on Earth, especially if there actually was a northern hemisphere ocean as well. How did they form? Does this mean that rivers could form in a variety of ways, with or without plant life being involved? Could Mars have once had something equivalent to vascular plant life as well? Or could the new theory just be wrong? Then there’s Titan, which has numerous rivers still flowing today. Albeit they are liquid methane/ethane instead of water, but what exactly led to their formation?

From the editorial in Nature Geoscience:

Without the workings of life, the Earth would not be the planet it is today. Even if there are a number of planets that could support tectonics, running water and the chemical cycles that are essential for life as we know it, it seems unlikely that any of them would look like Earth. Even if evolution follows a predictable path, filling all available niches in a reproducible and consistent way, the niches on any Earth analogue could be different if the composition of its surface and atmosphere are not identical to those of Earth. And if evolution is random, the differences would be expected to be even larger. Either way, a glimpse of the surface of an exoplanet — if we ever get one — may give us a whole new perspective on biogeochemical cycling and geomorphology.

Just as the many exoplanets now being found are of a previously unknown and amazingly wide variety, and all uniquely alien, even the ones that (may) support life are likely to be just as diverse from each other as they are from Earth itself. Earth’s “twin” may be out there, but in terms of outward appearance, it may be somewhat more of a fraternal twin than an exact replica.

Posted on by Paul Scott Anderson

Hayabusa 2 Mission Approved by Japanese Government

Artist's conception of Hayabua 2 approaching the asteroid 1999 JU3. Credit: Akihiro Ikeshita/JAXA

[/caption]

In 2010, the Japanese spacecraft Hayabusa completed an exciting although nail-biting mission to the asteroid Itokawa, successfully returning samples to Earth after first reaching the asteroid in 2005; the mission almost failed, with the spacecraft plagued by technical problems. The canister containing the microscopic rock samples made a soft landing in Australia, the first time that samples from an asteroid had been brought back to Earth for study.

Now, the Japanese government has approved a follow-up mission, Hayabusa 2. This time the probe is scheduled to be launched in 2014 and rendezvous with the asteroid known as 1999 JU3 in mid-2018. Samples would again be taken and returned to Earth in late 2020.

1999 JU3 is approximately 914 metres (3,000 feet) in diameter, a little larger than Itokawa, and is roughly spherical in shape, whereas Itokawa was much more oblong.

As is common for any space agency, the Japanese Aerospace Exploration Agency (JAXA) is working with tight budgets and deadlines to make this next mission happen. There is a possibility of a back-up launch window in 2015, but if that deadline is also not met, the mission will have to wait another decade to launch.

The asteroid Itokawa, visited by Hayabusa in 2005. Credit: JAXA

One of the main problems with Hayabusa was the failure of the sampling mechanism during the “landing” (actually more of a brief contact with the surface with the sample capturing device) to retrieve the samples for delivery back to Earth. Only a small amount of material made it into the sample capsule, but which was fortunate and ultimately made the mission a limited success. The microscopic grains were confirmed to have primarily come from Itokawa itself and are still being studied today.

To avoid a repetition of the glitches experienced by Hayabusa, some fundamental changes needed to be made.

This next spacecraft will use an updated ion propulsion engine, the same propulsion system used by Hayabusa, as well as improved guidance and navigation systems, new antennas and a new altitude control system.

For Hayabusa 2’s sample-collecting activities, a slowly descending impactor will be used, detonating upon contact with the surface, instead of the high-speed projectile used by Hayabusa. Perhaps not quite as dramatic, but hopefully more likely to succeed. Like its predecessor, the main objective of the mission is to collect as much surface material as possible for delivery back home.

Hopefully Hayabusa 2 will not be hampered by the same problems as Hayabusa; if JAXA can achieve this, it will be exciting to have samples returned from a second asteroid as well, which can only help to further our understanding of the history and formation of the solar system, and by extrapolation, even other solar systems as well.

Posted on by Paul Scott Anderson

Canada Looks to the Future in Space

The Canadarm on the Space Shuttle. Credit: NASA

[/caption]

When it comes to space, the first thing most people think of is NASA. Or Russia and the European Space Agency, or even more recently, countries like China and Japan. In the public eye, Canada has tended to be a bit farther down on the list. There is the Canadian Space Agency, but it is better known for developing space and satellite technologies, not awe-inspiring launches to the Moon or other planets, which naturally tend to get the most attention.

Canada has its own astronauts, too, but they go into orbit on the Space Shuttle or Russian rockets. Canada’s role in space should not, however, be underestimated. It was, for example, the first country to have a domestic communications satellite in geostationary orbit, Anik A1, in 1972. There is also the well-known Canadarm used on the Space Shuttle and Canadarm2 on the International Space Station, as well as the space robot Dextre on the ISS. Canada has also contributed technology to various robotic planetary missions as well.

But even in these times of budget constraints, new ventures are being planned, including a mission to place two video cameras on the International Space Station late next year, via a Russian mission.

The cameras will provide near real-time video broadcasting continuously in high-definition. The cameras are being developed by Urthecast, a Vancouver-based firm, which is investing $10 million in the project.

Like their American counterparts now, the investment and development of space technology is coming increasingly from the private sector instead of the government. In 1996, the Canadian government contributed 32% to domestic space revenue; in 2010, it was only 18% and it is estimated to drop again over the next three years.

Because of smaller budgets, the CSA focuses on assisting with larger missions from other countries instead of developing its own launch vehicles. According to Mark Burbidge, head of industrial policy at the CSA, the Canadian Space Agency doesn’t have the money for such projects. “That got our astronauts up there,” he says, referring to the Canadarm.

Another area that Canada may be able to contribute to is space tourism, a prime example of private companies becoming involved in the space business. Companies like SpaceX, Virgin Galactic and Bigelow Airspace are changing the way that people will go into near-orbit and low-Earth orbit. No dependence solely on government dollars to finance their objectives such as tourist space flights, small orbiting hotels or launching commercial satellites.

At this stage, government funding is still often required, especially for smaller firms, but the future looks promising. Space companies are becoming gradually less reliant on the government for revenue growth. The investment return tends to be primarily a scientific one, according to Dr. Jean de Lafontaine, founder of space services company NGC Aerospace in Quebec, making space tourism more of an ideal option for private companies.

This would seem to be an optimum arrangement, allowing companies to compete in orbital missions and tourism, while government agencies like NASA, ESA, etc. are better able to invest in larger-scale planetary missions and other costly space projects (noting however that some commercial companies also have their eyes on the Moon and Mars).

Canada may not have its own rockets or grandiose space missions, not yet anyway, but it will continue to make important contributions to space exploration. And as a Canadian, I am very pleased about that!

Posted on by Paul Scott Anderson

‘Oceanus Borealis’ – Mars Express Finds New Evidence for Ancient Ocean on Mars

Topographic map from Mars Global Surveyor showing colour-coded altitudes; the blue areas are the lowest and correspond to the possible ancient ocean in the northern hemisphere. Credit: NASA/JPL

[/caption]

For a long time now, evidence has continued to indicate that Mars was once a water world – near-surface groundwater, lakes, rivers, hot springs and, according to some planetary models, even an ancient ocean in the northern hemisphere. That last one in particular has been a subject of intense debate; some scientists see evidence for it while others do not. Even if it was there, it may have been a warm ocean or it may have been colder, like the polar seas here on Earth. The prospect of an ocean of any kind on early Mars is an exciting one, regarding the question of possible life way back then. The argument has swung both ways over the years, but now another new report has been published which comes down on the “yes” side.

The results come from the Mars Express Orbiter – specifically its ground-penetrating radar (MARSIS) and they have just been published in Geophysical Research Letters by Jérémie Mouginot from the University of California. The findings reinforce the idea of a large ocean which occupied much of the northern hemisphere, also known as Oceanus Borealis.

The radar has mapped the sedimentary deposits within the region, known as the Vastitas Borealis Formation, which are about 100 metres (328 feet) thick and overlie deeper volcanic deposits. Significantly, the mapping of the dielectric constant showed that the sedimentary deposits left over from the putative ocean differ from volcanic rock – they have a value of about 4-5, while volcanic deposits have a value of 9, 10 or even higher. Pure ice has a value of 3.1.

According to the research team, “Although much is still unknown about the evolution and environmental context of a Late Hesperian ocean, our observations provide persuasive evidence of its existence by the measurement of a dielectric constant of the Vastitas Borealis Formation that is sufficiently low that it can only be explained by the widespread deposition of (now desiccated) aqueous sediments or sediments mixed with massive ice.”

The big question has always been, if there was an ocean, where did all the water go? Additional radar mapping from Mars Express has shown that there are massive amounts of water ice buried beneath the surface, notably at the poles as well as within the speculative shorelines of the old ocean and even closer to the equator than was previously thought. It might seem reasonable to conclude then that much of the water from the ocean, and perhaps other seas or lakes as well, is still there, but now frozen solid.

It’s interesting to note also that the Phoenix lander, which landed within the Vastitas Borealis Formation in 2008, found water ice deposits only a few centimetres below the surface.

“As such, the formation represents the best geologic evidence to date for the existence of an ocean in the Late Hesperian, about 3 billion years ago,” the researchers said.

From the abstract:

A number of observations suggest that an extended ocean once covered a significant part of the Martian northern hemisphere. By probing the physical properties of the subsurface to unprecedented depth, the MARSIS/Mars Express provides new geophysical evidences for the former existence of a Late Hesperian ocean. The Vastitas Borealis formation, located inside a putative shoreline of the ancient ocean, has a low dielectric constant compared with that of typical volcanic materials. We show that the measured value is only consistent with low-density sedimentary deposits, massive deposits of ground-ice, or a combination of the two. In contrast, radar observations indicate a distribution of shallow ground ice in equilibrium with the atmosphere in the south polar region. We conclude that the northern plains are filled with remnants of a late Hesperian ocean, fed by water and sediments from the outflow channels about 3 Gy ago.

The full article can be purchased here ($25.00 U.S.).

Posted on by Paul Scott Anderson

Mystery Moon Flashes Caused by Meteorite Impacts

Example of a lunar flash, photographed in 1953. Credit: Leon Stuart/Columbia University Department of Astronomy

[/caption]

For hundreds of years, people have seen tiny flashes of light on the surface of the Moon. Very brief, but bright enough to be seen from Earth, these odd flashes still hadn’t been adequately explained up until now. Also known as Transient Lunar Phenomena (TLPs), they’ve been observed on many occasions, but rarely photographed. On Earth, meteorites burning up in the atmosphere can produce similar flashes, but the Moon has no atmosphere for anything to burn up in, so what could be causing them? As it turns out, according to a new study, the answer is still meteorites, but for a slightly different reason.

The lights don’t result from burning up as on Earth, but rather are hot blobs of material produced by the impact itself. The impacts were calculated to be powerful enough to melt the meteorites, producing super hot liquid droplets, called melt droplets, that produced light as they formed and then began to cool afterwards. The meteorites themselves can be tiny, but still cause an impact that could be seen from Earth.

Sylvain Bouley, a planetary scientist at the Paris Observatory and co-author of the study, explains: “You have just a small piece of cometary material or asteroid, about 10 centimeters, that can do a very bright flash visible from the Earth.”

Fellow planetary scientist Carolyn Ernst of Johns Hopkins University’s Applied Physics Laboratory, adds: “Something is melting, and because it’s so hot, it radiates in the visible wavelength until it cools down.”

The study included observations from 1999 – 2007, for which the brightness of the flashes and sizes and speeds of the meteorites were calculated.

The impacts have also been replicated at the Meteoroid Environment Office at the Marshall Space Flight Center, where tiny aluminum spheres were shot into simulated lunar dirt. The results were similar, helping to confirm the other team’s findings.

Other previous possible explanations included reflections on the Moon by tumbling satellites or even volcanic activity. There may still be debate though, as an earlier report in 2007 had attributed the flashes to outgassing on the Moon’s surface.

The paper will be published in the March 2012 issue of Icarus.

Posted on by Paul Scott Anderson

New Research Suggests Fomalhaut b May Not Be a Planet After All

The Fomalhaut b photograph. Credit: NASA, ESA, and P. Kalas (University of California, Berkeley, USA)

[/caption]

When the Hubble Space Telescope photographed the apparent exoplanet Fomalhaut b in 2008, it was regarded as the first visible light image obtained of a planet orbiting another star. The breakthrough was announced by a research team led by Paul Kalas of the University of California, Berkeley. The planet was estimated to be approximately the size of Saturn, but no more than three times Jupiter’s mass, or perhaps smaller than Saturn according to some other studies, and might even have rings. It resides within a debris ring which encircles the star Fomalhaut, about 25 light-years away.

Another team at Princeton, however, has just announced that they believe the original findings are in error, and that the planet is actually a dust cloud, based on new observations by the Spitzer Space Telescope. Their paper has just been accepted by the Astrophysical Journal.

According to the abstract:

The nearby A4-type star Fomalhaut hosts a debris belt in the form of an eccentric ring, which is thought to be caused by dynamical influence from a giant planet companion. In 2008, a detection of a point-source inside the inner edge of the ring was reported and was interpreted as a direct image of the planet, named Fomalhaut b. The detection was made at ~600–800 nm, but no corresponding signatures were found in the near-infrared range, where the bulk emission of such a planet should be expected. Here we present deep observations of Fomalhaut with Spitzer/IRAC at 4.5 µm, using a novel PSF subtraction technique based on ADI and LOCI, in order to substantially improve the Spitzer contrast at small separations. The results provide more than an order of magnitude improvement in the upper flux limit of Fomalhaut b and exclude the possibility that any flux from a giant planet surface contributes to the observed flux at visible wavelengths. This renders any direct connection between the observed light source and the dynamically inferred giant planet highly unlikely. We discuss several possible interpretations of the total body of observations of the Fomalhaut system, and find that the interpretation that best matches the available data for the observed source is scattered light from transient or semi-transient dust cloud.

Kalas has responded to the new study, saying that they considered the dust cloud possibility but ruled it out for various reasons. For one thing, Spitzer lacks the light sensitivity to detect a Saturn-sized planet, and bright rings could also explain the optical characteristics observed. He says, “We welcome the new Spitzer data, but we don’t really agree with this interpretation.”

The Princeton team, interestingly, thinks that there may be a real planet orbiting Fomalhaut, but still hiding from detection. From the paper:

In particular, we find that there is almost certainly no direct flux from a planet contributing to the visible-light signature. This, in combination with the existing body of data for the Fomalhaut system, strongly implies that the dynamically inferred giant planet companion and the visible-light point source are physically unrelated. This in turn implies that the ‘real’ Fomalhaut b still hides in the system. Although we do find a tentative point source in our images that could in principle correspond to this object, its significance is too low to distinguish whether it is real or not at this point.

A resolution to the debate may come from the James Webb Space Telescope, scheduled to launch in 2018.

Of course it will be disappointing if Fomalhaut b does turn out to not be a planet after all, but let’s not forget that thousands of other ones are being discovered and confirmed. There may occasionally be hits-and-misses, but so far the planetary hunt overall has been nothing short of a home run…

The paper is available here.

Posted on by Paul Scott Anderson

Cassini Takes a Closer Look at Titan’s Sand Dunes

Radar image of sand dunes on Titan. Credit: NASA/JPL–Caltech/ASI/ESA and USGS/ESA

[/caption]

Titan is a world that is amazingly Earth-like in some ways, with rain, rivers, lakes and seas. Mind you, the liquid in this case is methane/ethane instead of water, at the bitterly cold conditions on the surface. Also like Earth, Titan has vast sand dune fields, covering about 10 million square kilometres (39 million square miles), or 13% of Titan’s surface. The Cassini spacecraft has been studying these dunes with its radar (in order to see through the perpetually smog-like atmosphere), with interesting results.

Titan’s dunes show regional differences, although they are only found in equatorial areas, between 30°S and 30°N. They are found in both highlands and lowlands, but primarily in lower elevations. The ones at higher altitudes are thinner and more widely spaced, and the gaps between them are brighter in the radar images, which means that there is probably less sand available than at lower altitudes. The dunes also become narrower and more widely spaced at northern latitudes.

Comparison of dunes on Titan (left) with those on Earth (right). Credit: NASA/JPL–Caltech/ASI/ESA and USGS/ESA

Because Titan’s southern hemisphere has shorter but more intense summers, due to Saturn’s elliptical orbit around the Sun, there is less moisture in the soil in those regions, making them more ideal for dune-forming. There is more moisture in the northern regions, where most of the lakes and seas are found.

“As one goes to the north, the soil moisture probably increases, making the sand particles less mobile and, as a consequence, the development of dunes more difficult,” said Dr. Le Gall of LATMOS-UVSQ in Paris.

The characteristics of Titan’s dunes also provide clues to the moon’s climate and geological history.

According to Nicolas Altobelli, Cassini–Huygens project scientist, “Understanding how the dunes form as well as explaining their shape, size and distribution on Titan’s surface is of great importance to understanding Titan’s climate and geology. As their material is made out of frozen atmospheric hydrocarbons, the dunes might provide us with important clues on the still puzzling methane/ethane cycle on Titan, comparable in many aspects with the water cycle on Earth.”

It should also be noted that the sand on Titan is composed of solid hydrocarbons instead of silicates like sand on Earth. Similar in appearance, but like the rest of Titan, very different in composition. They are reminiscent of the dune fields in Namibia or southern Arabia, but are much larger – they average about 1-2 kilometres (0.6-1.2 miles) wide, 100 metres (328 feet) tall and extend for hundreds of kilometres/miles!

It would be interesting to see a Titanian version of Lawrence of Arabia…