Mars Gully: No Mineral Trace Of Liquid Water

Excerpt:

"This CRISM image of a bright gully deposit was constructed by showing 2.53, 1.50, and 1.08 micrometer light in the red, green, and blue image planes. CRISM can just resolve the deposits (highlighted by arrows in the inset), which are only a few tens of meters (about 150 feet) across. The spectrum of the deposits barely differs from that of the surrounding material, and is just a little brighter. This difference could simply be explained by a slightly greater content of dust than in the surrounding soil. In contrast, older deposits elsewhere on Mars ( such as Valles Marineris) that do contain hydrated salts have distinctive spectral features near 1.9 and 3.0 microns. The gully deposits lack these features, and exhibit no evidence for water-deposited salts."

"Another new finding from that camera may help undermine arguments that very ancient Mars had a wet climate on a sustained basis. Landscapes with branched channels and fan-like deposits typical of liquid flows were found around several impact craters. Images show close association between some of those flow features and ponded deposits interpreted as material melted by the impact of a meteoroid into ice-rich crust.

"This new evidence supports a hypothesis that ancient water flows on the surface were episodic, linked to impact events and subsurface heating, and not necessarily the result of precipitation in a sustained warmer climate. Crater-digging impacts were larger and more numerous during the early Martian era when large drainage networks and other signs of surface water were carved on many parts of the planet."