The most common kind of Martian meteorite. First discovered in Shergotty, India, in 1865, these rocks originally come from Martian volcanoes. Shergottites (one shown left) give geologists clues to the composition of Mars’ mantle, the layer beneath the crust. Geologists J. Brian Balta and Harry Y. McSween Jr. of the University of Tennessee say that data from shergottites, and from Mars missions such as the Spirit and Opportunity rovers, indicate that the Red Planet’s mantle was once wet but lost its water through degassing. Volcanoes may have brought the water to Mars’ surface, where it could have weathered rocks to clays and even supported life, the researchers report July 30 in Geology.