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A Hitchhiker's Guide to Astrobiology

Looking for Microbial Martians

Space on Earth

A conference on Mars Polar Science recently met in Davos, Switzerland. By studying the poles, scientists are learning about the history of water on the planet, and how that has affected Mars' potential for life.

Martian Methane Ice

Martian Poles in the Swiss Alps

The alpine village of Davos, seen from Weissfluhjoch. Click image for larger view.
Image Credit: Leslie Mullen

The Fourth International Conference on Mars Polar Science and Exploration was recently held in Davos, Switzerland. It was an appropriate meeting place for those who study cold regions, because as Walter Ammann of the Swiss Federal Institute for Snow and Avalanche Research noted, "We like to joke that in Davos, we have 9 months of winter, and 3 months of cold."

Snow had not yet accumulated on the Alps that tower over the small village, but the proximity to nearby mountains and glaciers provided inspiration to the over one hundred scientists who met to discuss recent findings about the martian poles.

One conclusion generally shared during this meeting is that what we learn about the poles can teach us about the history of the entire planet. Steve Clifford of the Lunar and Planetary Institute was one of the conference organizers, and his words from the polar conference three years ago are more resonant today than ever: "All Mars science is polar science."

The first half of the meeting focused on the complexity and history of the polar regions. The south pole's many ice layers were analyzed in great detail. Because of their complexity, instead of calling the region a "polar cap" many of the scientists preferred to call it the "polar layered deposits," or PLD. Rather than just draping over the landscape, these white layers may be somehow independent of the underlying topography.

This MARCI image from MRO is a composite mosaic of the north polar cap. The images were taken at midnight, 6 a.m., noon, and 6 p.m. martian time, during the summer when the sun is always shining in the polar region. The image shows the mostly water-ice perennial cap (white area), sitting atop the north polar layered materials (light tan immediately adjacent to the ice), and the dark circumpolar dunes.
Image Credit: NASA/JPL/MSSS

Jeff Plaut, a co-Principal Investigator on the European Space Agency's Mars Express MARSIS radar instrument, presented a nearly complete radar map of the south polar region, and helped the scientists come to a better understanding of how the south pole is structured.

"With martian missions as frequent as they've been, we've been able to benefit from the fact that there's always a great deal of new data to talk about," Clifford said. "With the first meeting in Houston in 1998, we were just beginning to get some of the early Mars Global Surveyor results. We'd had an opportunity to analyze many of those results by the time of the Iceland meeting in 2000, but there was also the absolute depression of having just lost the Mars Polar Lander -- that was agonizing. But then by the time of Lake Louise in 2003, we had the Mars Odyssey results that suggested there was water ice in the near surface. And now with this meeting, we're finally able to talk about the radar results for Mars. That's something we've been anticipating since the first meeting -- to be able to trace layers within the interior of the cap, and not just see what's exposed on the scarps and the troughs. Hopefully we'll have the same kind of coverage by the next meeting for the north polar cap, and with higher resolution with the Mars Reconnaissance Orbiter's SHARAD experiment."

The north pole is quite different than the south, but it is equally complex. There may be between 17 to 25 major layers in the north pole, and a newly-released image by the Mars Reconnaissance Orbiter showed some of these layers -- bands of light and dark that looked reminiscent of the rings of Saturn.

MRO HiRISE image of the north polar layered deposits, taken during the summer when carbon dioxide frost had evaporated from the surface. Layers at the bottom of the image are visible due to differences in slope between them. The slope variations are probably caused by differences in the physical properties of the layers. Thinner layers may represent annual deposition of water ice and dust.

The amount of dust in the atmosphere may play an important role in the formation of the polar layers, making them almost like tree rings, where each layer will tell a different story about the environment in which it formed.

Learning the history of the poles goes to the heart of understanding not only how they came to be, but how they have played a role in shaping the rest of the planet. Mars's geologic and climatic history seems to be intimately tied into the obliquity, or tilt, of the planet as it orbits the sun. Unlike Earth, Mars has not enjoyed a stable tilt over the eons -- it alters in approximately one hundred thousand-year cycles. The orbit of Mars around the sun also changes over time. These two "astronomical" factors have likely resulted in the polar ice being transferred around the planet as it swings around the sun at different angles and distances. Many of the recent photos of Mars showing evidence of water flow on the surface may be the result of this change in obliquity and orbit, and the subsequent migration of the ice.

The second half of the meeting focused on current and future Mars polar missions. The Mars Reconnaissance Orbiter is now sending back intensely detailed photos of the polar regions, as well as other types of data, and this will be important information to have at hand when selecting a landing site for the Phoenix Lander, which is due to be launched in 2007. In fact, one of the first MRO images transmitted was of the potential Phoenix landing site in the high northern latitudes. One question brought up by this image was how did the rocks strewn about the surface get there? Are they meteorites? Were they deposited by past glacial movement? Or did some other unknown process put them there?

HiRISE image of a potential Mars Phoenix landing site. The polygonal patterned ground looks similiar to permafrost regions of Earth. The diameters of these martian polygons are dominantly 10 to 20 meters (but some are a few meters or less wide). Rocks protruding above the surface soil cast shadows, which can aid in the determination of the rock's size and height.

If it successfully lands, Phoenix will verify the findings of Mars Odyssey, which discovered substantial amounts of hydrogen in the surface (interpreted to be water ice, H2O). Phoenix will study the history of the northern permafrost, and see if the soil has ever been altered by the ice melting into liquid. Phoenix also will study the polar climate, and determine the habitability of the icy soil. As Peter Smith, Principal Investigator for Phoenix Lander noted, one-third of all soil carbon on Earth is locked up in the northern permafrost. Therefore the northern region of Mars is considered a great place to look for organics.

Although the Mars mission for 2011 has not yet been selected, there is much hope among polar scientists that the mission will include a drill to investigate deep into the ice. A thermal drill is being developed by the Jet Propulsion Laboratory with 2011 in mind, and Michael Hecht described this project -- called CHRONOS -- in some detail, explaining the mission goals and the difficulties they've encountered so far.

By the end of the conference, the tops of the Alps were dusted with new-fallen snow, and Davos was well on its way to becoming a winter wonderland for skiers. While skiing on Mars is not yet a possibility for even our robotic explorers, the onset of the ski season provides Mars polar scientists with a reminder of the changeability of the martian poles -- what was at one time barren rock then becomes covered with ice, and then changes back again. While martian seasons may not be as regular as Earth's, the Mars Polar Science conference showed that we may be getting much closer to understanding them.

By Leslie Mullen