This image shows a subsurface explorer on the surface of Mars (this is an artist's rendition). Such subsurface explorers would help us look for water and organic material below the surface of Mars. A "robotic mole" like this one would also test to see what minerals make up the Martian interior. One of the proposals does involve a subsurface explorer that would dive through the Martian polar ice caps.
Courtesy of NASA/JPL