NASA photos may point to recent water flow on Mars

It's not concrete, but scientists say images provide "the strongest evidence to date." Photos: Best evidence yet of liquid water flow on Mars

Photographs from NASA's Mars Global Surveyor may indicate some level of occasional liquid water flow on the surface of Mars.Gully on Mars

Though the Mars Global Surveyor may be lost in space, recent comparisons of images captured throughout the satellite's decade of observing the Red Planet have shown changes in surface geography that, scientists theorize, could be signs of water flow in several locations between 1999 and 2005.

These discrepancies in the presence of light-colored deposits in gullies on Martian craters are "what you would expect to see if the material were carried by flowing water," Michael Malin, of Malin Space Science Systems in San Diego, asserted in a statement from NASA. The findings were announced Wednesday.

Changes in the makeup of gullies on slopes, a topographical feature first noticed by Malin's research team in 2000, were first noticed after a gully appeared to form after mid-2002. It was, however, attributed to the flow of sand on a dune. But now, comparisons of earlier and more recent images have revealed new light-colored deposits that could possibly be related to ice or salt formations that would come from liquid water flow. Deposits caused by dry dust or sand are more likely to be dark in color.

It's by no means positive. But Michael Meyer, lead scientist for NASA's Mars Exploration Program, said that this is "the strongest evidence to date that water still flows occasionally on the surface of Mars."

Ice water and water vapor are known to exist on Mars, but up until this point, there has not been compelling evidence for the presence of liquid water. Due to Mars' thin atmosphere and subzero temperatures, liquid water--crucial for the sustenance of even the smallest microbial life--could not stay in that form for long. But researchers have suggested that it could be possible for liquid water to escape from underground and stay liquid for long enough to alter surface deposits in the way that the evidence from the Mars Global Surveyor shows.

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