Woah. If this is confirmed, it's big.

New analysis of Mars Rover images taken a couple of years ago in the "Endurance" crater seem to show standing pools of water on the Martian surface.

Along with fellow Lockheed engineer Daniel Lyddy, [physicist Ron] Levin used images from the Jet Propulsion Laboratory's website. The resulting stereoscopic reconstructions, made from paired images from the Opportunity 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.

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.

This would greatly boost the likelihood of finding near-surface Martian life; in fact, the father of one of the authors, Gilbert Levin, laid out the evidence for Martian life (PDF) in a paper delivered at the Carnegie Institution Geophysical Laboratory last month, relying in part on the water discovery. Gilbert Levin was principal investigator on the Viking lander experiment that appeared to show signs of life.

The main argument against this idea is that the density of the Martian atmosphere is so close to vacuum that water coming to the surface should just sublime away instantly. But some areologists have proposed that water may be able to exist for longer periods on the surface if certain conditions are met -- conditions that are most likely to occur in deep craters like Endurance.

Update: It looks like Ron Levin didn't do his homework on this. Follow the link Peter Erwin provides in the comments. Short version: the image that Levin processed for his research turns out, when examined in context, to be part of a tilted cliff face, not a horizontal surface -- not a good spot for still water.