Even while snared in a sand trap, NASA’s Mars rover Spirit has hit “wet” pay dirt: evidence of relatively recent groundwater activity on the red planet. For almost six months the rover has been precariously perched on the edge of a shallow crater in an equatorial region of Mars. The area is filled with cooled lava flows pitted by meteorite impacts. While on a routine drive, Spirit broke through a thin crust of hard soil that capped a filled-in impact crater, and its wheels became half buried in the soft sand.