Scientists report they've failed to find hard evidence that water flowed on Mars within the last decade.
The finding casts doubt on the 2006 report that the bright spots in some Martian gullies indicate that liquid water flowed down those gullies sometime since 1999.
"It rules out pure liquid water," said lead author Jon D. Pelletier of The University of Arizona in Tucson.
Pelletier and his colleagues used topographic data derived from images of Mars from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. Since 2006, HiRISE has been providing the most detailed images of Mars ever taken from orbit.
The researchers applied the basic physics of how fluid flows under Martian conditions to determine how a flow of pure liquid water would look on the HiRISE images versus how an avalanche of dry granular debris such as sand and gravel would look.
"The dry granular case was the winner," said Pelletier, a UA associate professor of geosciences. "I was surprised. I started off thinking we were going to prove it's liquid water."
Finding liquid water on the surface of Mars would indicate the best places to look for current life on Mars, said co-author Alfred S. McEwen, a UA professor of planetary sciences.
"What we'd hoped to do was rule out the dry flow model -- but that didn't happen," said McEwen, the HiRISE principal investigator and director of UA's Planetary Image Research Laboratory.