NASA's Mars Reconnaissance Orbiter (MRO) is examining several features on Mars such as material deposited in two gullies within the past eight years, polar ice layers formed in the recent geologic past, and signs of water released by large impacts when Mars was older. All those features address the role of water at different times in the planet's history. While previous discoveries have raised hopes that modern flows of liquid water had been detected on Mars, recent observations have suggested otherwise. The big question is whether water is coming to the surface of Mars today.
Also, 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. This finding may help undermine arguments that very ancient Mars had a wet climate on a sustained basis. The MRO has also examined ice-rich layered deposits near the Martian poles with the ground-penetrating Shallow Subsurface Radar instrument, and other experiments. The radar detected layering patterns near the south pole that suggest climatic periods of accumulating deposits have alternated with periods of erosion. These observations add to other evidence that the layers are mostly water.
http://www.marstoday.com/news/viewpr.html?pid=23578
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