Recent Seasonal Flows
Liquid water cannot exist on the surface of Mars with its present low atmospheric pressure and low temperature, except at the lowest elevations for a few hours. So, a geological mystery commenced when observations from NASA's Mars Reconnaissance Orbiter revealed gully deposits that were not there ten years ago, possibly caused by flowing salty water (brine) during the warmest months on Mars. The images were of two craters called Terra Sirenum and Centauri Montes which appear to show the presence of liquid water flows on Mars at some point between 1999 and 2001. In August 2011, NASA announced the discovery by Nepalese student Lujendra Ojha of current seasonal changes in gullies near crater rims on the Southern hemisphere. The researchers again suggested salty water (brines) flowing and then evaporating, possibly leaving some sort of residue.
There is disagreement in the scientific community as to whether or not the recent gully streaks were formed by liquid water. A team suggests the flows were merely dry flows, dry flows that were started by a rock fall in steep regions, or liquid brine near the surface might explain this activity, but the exact source of the water and the mechanism behind its motion are not understood.
Read more about this topic: Water On Mars
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