Mars rover finds "puddles" on the planet's surface

This article is based on a preprint by two scientists and a news story in New Scientist magazine, a publication (like our own) developing a reputation for publishing science news that most other publications are not ready to cover because they can’t get an okay from “authorities” such as NASA. See http://space.newscientist.com/article/dn12026-mars-rover-finds-puddles-on-the-planets-surface.html for the news story.

The preprint by R. L. Levin and Daniel Lyddy is titled “Investigation of possible liquid water ponds on the Martian surface” (2007 IEEE Aerospace Applications Conference Proc., paper #1376, to be published in IEEE Xplore). Both authors are at the aerospace company Lockheed Martin in Arizona. Levin is a physicist and an expert in advanced image processing, and the original images for this analysis are posted to the Jet Propulsion Laboratory's website. Lyddy is an engineer.

Levin’s father Gilbert was principal investigator of an experiment on the Viking Mars landers in 1976, which found evidence for life on the planet. Negative results from a separate test for organic materials led most scientists to doubt the evidence for biology. But subsequent research showed that the organic molecule detection instrument was insufficiently sensitive and also failed to detect organics in a sample from Antarctica containing a known virus.

A new analysis of pictures taken early in its mission by the Mars rover Opportunity reveals what appear to be small ponds of liquid water on the surface of Mars. See the cover photo for this issue.

Specific spots appear to have contained liquid water in 2003, when Opportunity was exploring a crater called Endurance. However, this interpretation of the images is highly controversial because many scientists still believe that liquid water cannot exist on the surface of Mars today because the atmospheric pressures on Mars are too low. Moreover, the existence of such ponds would significantly boost the odds that living organisms could survive on or near the surface of Mars. Therefore, much is at stake in interpreting these images correctly.

In this new analysis, stereoscopic reconstructions made from paired images from the rover's twin cameras show bluish features that look perfectly flat. The surfaces are so smooth that the computer could not find any surface details within those areas to match up between the two images.

Apparently, the flat areas occupy the lowest parts of the terrain. They also appear transparent: some features that may be submerged rocks or pebbles appear below the plane of the smooth surface.

The smoothness and transparency of the features could be due to either water or very clear ice. However, ice or some other material should show evidence of surface erosion, such as rubble or sand or other surface irregularities.

Images from orbit led to reports last year showing the existence of gullies on crater walls where water appears to have flowed in the last few years. Those are short-lived flows and are thought to have frozen over almost immediately. Standing liquid water has not been previously recognized as such.

Theory indicates a range of temperatures and pressures where liquid water might be stable on Mars. Such conditions might exist in “micro-environments” with special conditions, such as regions with hot springs on Earth. But it is difficult to find general conditions on Mars that could support liquid water, although the absence of winds with significant force is a big help.

Perhaps the most promising explanation is the “briny water” theory. It is likely that any water on Mars would contain dissolved salts, and these would extend the range of stability significantly. When combined with wind-sheltered locations such as the interior of Endurance crater, and temperatures found at mid-day in the Martian summer, stable liquid water states are feasible.

The rover is now far from Endurance crater. However, if similar features are found elsewhere in the rover’s explorations, Levin proposes a simple test that would prove or disprove the presence of liquid. Simply use the rover's drill on the surface of the flat area. If it is ice or any solid material, the drill will leave unmistakable markings. But if it is liquid there should be no trace of the drill's activity.

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