Spirit's Feb. 27 photograph of a two-foot-tall rock called "Humphrey" -- named after Humphries Peak in Arizona.
Two robotic geologists continue their hard at work on the surface of Mars. The rover named Spirit is making detailed studies of a rock known as Humphrey. Spirit's twin, the rover called Opportunity, continues to study of an outcrop of rocks that scientists think are part of the Martian bedrock.
NASA's Mars missions present a rare opportunity to follow along with a space science mission in real time. NASA is posting pictures taken by both rovers' cameras on a public Web site almost as soon as they arrive on earth.
NPR's Joe Palca joins NPR's John Ydstie to do a little Mars exploration from the comfort and safety of a radio studio.