Scientists in the USA decided to retake images of the gullies to search for any sign of recent activity.
Two of those originally photographed in 1999 and 2001 then photographed again in 2004 and 2005 showed changes consistent with water having flowed down the side of the crater. The discovery was made by scientists at the San Diego-based Malin Space Systems which operated a camera aboard the spacecraft.
Writing in the journal Science, the researchers led by Michael Malin said the properties and settings of the deposits in the gullies are consistent with water flow.