Researchers say they have identified traces of ice in craters on Mercury, seen here in this Oct. 8, 2008, image from the Messenger spacecraft. NASA hide caption

itoggle caption NASA

NASA's Mars rover Curiosity dug up five scoops of sand from a patch nicknamed "Rocknest." A suite of instruments called SAM analyzed Martian soil samples, but the findings have not yet been released. NASA/JPL-Caltech hide caption

itoggle caption NASA/JPL-Caltech

Untitled, by South African artist Gavin Jantjes, is one of the works in the "African Cosmos" exhibition. National Museum of African Art hide caption

itoggle caption National Museum of African Art

An artist's impression shows a planet, right, orbiting the star Alpha Centauri B, center, a member of the triple star system that is the closest to Earth. ESO/L. Calcada/AP hide caption

itoggle caption ESO/L. Calcada/AP