Orbiter spots possible water seepage on surface of Mars

[DainBramaged]

Over the last several decades, evidence has piled up that Mars once played host to liquid water on its surface. But in its current geological era, the red planet is too cold and has too little atmosphere to allow liquid to survive for long. Even at the peak of Martian summer, water would evaporate off quickly during the day, or freeze solid as soon as night hit. But that doesn't mean it couldn't exist beneath the surface, where pressures and temperatures might be quite different, so researchers have been looking for signs that some subterranean liquid might bubble to the surface. Now, scientists are reporting some changes on the Martian surface that seem to be best explained by a watery seep.

The information comes courtesy of the finest resolution camera we've ever put in orbit there, the High Resolution Imaging Science Experiment (HiRISE) on the Mars Reconnaissance Orbiter. The MRO has been circulating Mars for long enough that it's been able to image certain areas multiple times over a Martian year or more, which has enabled the authors of a new paper to identify seasonal changes on the planet's surface.

One of the changes that the authors spotted was a "recurring slope lineae," or RSL (their name, not ours). These were regions of steep downward slopes (25 degrees or more) that darkened during the Martian summer and reverted to a lightened color once summer ended. These were mostly concentrated in the southern hemisphere, but tended to be on northward-facing slopes, suggesting they required elevated temperatures to form. They were also associated with channels that are visible year-round, and they appeared to flow around obstacles, rather than simply barreling down-slope. Typically, they appeared at the base of a bedrock outcrop; in a few locations, hundreds of these RSLs were present.

Overall, the authors have confirmed 7 sites with RSLs, and have a strong indication of another dozen—the latter just haven't been imaged long enough to confirm their annual reappearance. Another 20 sites appear to be worth following up on. Each site hosts anywhere from a dozen to thousands of these features on different areas of the slope, each less than five meters across.

http://arstechnica.com/science/news/2011/08/seasonal-changes-on-mars-hint-at-watery-flows.ars