The latest research emerged when Nasa's Mars Global Surveyor (MGS) spacecraft spotted gullies and trenches that scientists believed were geologically young and carved by fast-moving water coursing down cliffs and steep crater walls.
Scientists at the San Diego-based Malin Space Science Systems, who operate a camera aboard MGS decided to retake photos of thousands of gullies in search of evidence for recent water activity.Two gullies that were originally photographed in 1999 and 2001, and imaged again in 2004 and 2005, showed changes consistent with water flowing down the crater walls, according to the study.
In both cases, scientists found bright, light-coloured deposits in the gullies that were not present in the original photos. They concluded that the deposits - possibly mud, salt or frost - were left there when water recently cascaded through the channels.
http://news.bbc.co.uk/2/hi/science/nature/6214834.stm
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