Four years after they landed on Mars, NASA s twin robot explorers, Spirit and Opportunity, have lasted 16 times longer and driven 20 times farther than expected. Today they are joined by an aerial armada of hi-tech satellites, surveying Mars from orbit to reconstruct the planet s mysterious history. And on May 25, 2008, they also got company on the ground: NASA s Phoenix probe. NOVA s Is There Life on Mars? showcases the latest scientific revelations from a planet, once alien, now poised to reveal provocative new clues in the tantalizing quest to plumb its past for signs of water and, perhaps, even life.