杏吧原创

Update: The researchers have retracted their claim about the possibility of standing water on Mars after readers pointed out the terrain lies on the sloped wall of a crater 鈥� see our blog explaining what happened.

A new analysis of pictures taken by the exploration rover Opportunity reveals what appear to be small ponds of liquid water on the surface of Mars.

The report identifies specific spots that appear to have contained liquid water two years ago, when Opportunity was exploring a crater called Endurance. It is a highly controversial claim, as many scientists believe that liquid water cannot exist on the surface of Mars today because of the planet鈥檚 thin atmosphere.

If confirmed, the existence of such ponds would significantly boost the odds that living organisms could survive on or near the surface of Mars, says physicist Ron Levin, the report鈥檚 lead author, who works in advanced image processing at the aerospace company Lockheed Martin in Arizona.

Along with fellow Lockheed engineer Daniel Lyddy, Levin used images from the Jet Propulsion Laboratory鈥檚 website. The resulting stereoscopic reconstructions, made from paired images from the Opportunity rover鈥檚 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.

The imaging shows that the areas occupy the lowest parts of the terrain. They also appear transparent: some features, which Levin says may be submerged rocks or pebbles, can be seen below the plane of the smooth surface.

Smooth surface

The smoothness and transparency of the features could suggest either water or very clear ice, Levin says.

鈥淭he surface is incredibly smooth, and the edges are in a plane and all at the same altitude,鈥� he says. 鈥淚f they were ice or some other material, they鈥檇 show wear and tear over the surface, there would be rubble or sand or something.鈥�

His report was presented at a conference of the Institute of Electrical and Electronics Engineers, and will be published later this year in the institute鈥檚 proceedings.

No signs of liquid water have been observed directly from cameras on the surface before. Reports last year pointed to the existence of gullies on crater walls where water appears to have flowed in the last few years, as shown in images taken from orbit, but those are short-lived flows, which are thought to have frozen over almost immediately.

Speedy evaporation?

Levin and other reasearchers, including JPL鈥檚 Michael Hecht, have published calculations showing the possibility of 鈥渕icro-environments鈥� where water could linger, but the idea remains controversial.

鈥淭he temperatures get plenty warm enough, but the Mars atmosphere is essentially a vacuum,鈥� says Phil Christensen of Arizona State University, developer of the Mars rovers鈥� mini-Thermal Emission Spectrometers. That means any water or ice exposed on the surface evaporates or sublimes away almost instantly, he says.

But, he adds, 鈥渋t is theoretically possible to get liquid water within soil, or under other very special conditions鈥�. The question is just how special those conditions need to be, and whether they ever really are found on Mars today.

If there were absolutely no wind, says Christensen, you might build up a stagnant layer of vapour above a liquid surface, preventing it from evaporating too fast. 鈥淭he problem is, there are winds on Mars聟 In the real world, I think it鈥檚 virtually impossible,鈥� he told New 杏吧原创.

Simple test

Levin disagrees. He says his analysis shows that there can be wind-free environments at certain times of day in certain protected locations. He thinks that could apply to these small depressions inside the sheltered bowl of Endurance crater, at midday in the Martian summer.

He adds that highly briny water, as is probably found on Mars, could be stable even at much lower temperatures.

Although the rover is now miles away from this site, Levin proposes a simple test that would prove the presence of liquid if similar features are found: use the rover鈥檚 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鈥檚 activity.

Levin鈥檚 father Gilbert was principal investigator of an experiment on the Viking Mars lander, which found evidence for life on the planet, although negative results from a separate test for organic materials led most scientists to doubt the evidence for biology.

Journal reference: R. L. Levin and Daniel Lyddy, Investigation of possible liquid water ponds on the Martian surface (2007 IEEE Aerospace Applications Conference Proceedings, paper #1376, to be published in )