NASA's Jet Propulsion Laboratory (JPL) Navigator Program Engineer Dr Randii Wessen discusses the Mars Exploration Rover (MER) beside a model of the MER in a "sandbox" at the JPL in Pasadena, California, 21 January 2004. With the first rover named "Spirit" already safely on martian soil, engineers and scientists are gearing up for the scheduled landing of the second rover "Opportunity" on the opposite side of Mars later this week. AFP PHOTO / Robyn BECK COPYRIGHT SCANPIX SWEDEN Code: 444