In the summer of 2003, the NASA Mars Exploration Rover mission sent two rovers, named Spirit and Opportunity, to Mars to examine its geology and search for signs of water. The Spirit landed successfully on the Meridiani Planum of Mars on Jan. 4, 2004, but NASA scientists lost contact with it on Jan. 21. The apparent failure of the Spirit, coming just a month after the European Space Agency lost contact with its Mars lander, was a disappointing development in exploration of Mars.NASA regained contact with the Spirit on Jan. 23; two days later, the Opportunity landed in the Gusev Crater , on the opposite side of the planet from the Spirit. “We resurrected one rover and we saw the birth of another,” declared NASA associate administrator Ed Weiler. “This was one heck of a critical milestone.”Though the Spirit and Opportunity were originally planned to spend three months on Mars, both rovers remain on Mars as of January 2011 . Spirit has been stuck in a sand trap since May 2009 and might not be able to ever escape, but Opportunity is still functioning well.The Rovers have each found evidence that there was once water on the planet , and traveled approximately 13 miles. “This has turned into humanity's first overland expedition on another planet,” said Steve Squyres, an investigator for the mission. “When people look back on this period of Mars exploration decades from now, Spirit and Opportunity may be considered most significant not for the science they accomplished but for the first time we truly went exploring across the surface of Mars.”