The world's largest extraterrestrial explorer, NASA's Curiosity rover, is on its way to Mars. It is searching for evidence that the red planet might once have been home to life. The journey is a long one - 8 1/2/ months to cross the 354 million miles.The rover, officially known as Mars Science Laboratory, is as large as a car and weighs 2,000 pounds. The primary goal of the mission is to determine whether mars might have been hospitable for microbial life at some time in the past, or now.