In its eerie likeness to Earth, Mars has long captured our imaginations--both as a destination for humankind and as a possible home to extraterrestrial life. It is our twenty-first century New World; its explorers robots, shipped 350 million miles from Earth to uncover the distant planet's secrets. Its most recent scout is Curiosity--a one-ton, Jeep-sized nuclear-powered space laboratory--which is now roving the Martian surface to determine...