Three generations of rover

Known formally as the Mars Science Laboratory, Curiosity is the third in three generations of Mars rovers. In the middle here of this family portrait of scale models, in between Spirit/Opportunity at left and Curiosity at right, is the first generation, the Sojourner rover that landed in the Mars Pathfinder mission of 1997. The image, from May 2008, has the models posing in front of NASA's Jet Propulsion Laboratory in Pasadena, Calif.

The full-size, mission-ready Curiosity will stand about 7 feet tall, 9 feet wide, and 10 feet front to back, not counting its robotic arm. It'll weigh close to 2,000 pounds, making it much heftier than Spirit and Curiosity (about 384 pounds) and even more so than Sojourner (24 pounds).

Curiosity will be on the prowl for, among other things, organic molecules--which would indicate whether Mars was ever capable of supporting life. "The rock record is of particular interest," Crisp said in a statement. "It has a record from billions of years ago and can answer questions like 'Where and for how long might Mars have been habitable?' 'Was it cold or warm there in the past?' 'Was the water there acidic or salty?'"