At this very hour, the Mars exploration rover Spirit is searching for evidence of life beyond the Earth.

CNN: Bush: 'It is time for America to take the next steps' in space

"You take what Mars gives you, " said Squyres, also the lead scientist on the Mars Exploration Rover Mission, which includes Spirit and Opportunity.

CNN: Rover Curiosity near Mars landing

Before Curiosity, NASA's big rover project was the Mars Exploration Rover Mission: two golf-cart-sized rovers called Spirit and Opportunity.

CNN: What we've done on Mars, and what's next