 Using images captured by the Viking, Mars Express, Mars Reconnaissance Orbiter and Mars Odyssey missions, a 2008 study was able to identify a series of faults on the surface of Mars based on how their traces are expressed.These traces appear as erosion resistant ridges thought to have been formed by water deposited minerals within ancient fault zones.Finding these fault traces means that there may have been plate tectonics, geothermal interactions, and movement of ground water at some point in the planets history.