On Jan. 3, 2004, the Spirit rover landed in Gusev Crater on Mars, kicking off a mission planned to last 90-days. Two years later, Spirit and fellow robotic explorer Opportunity, which landed Jan. 24, 2004, are still going strong. Shortly after its landing, Opportunity found layered bedrock bearing geological evidence of a shallow ancient sea. More than one year later, Spirit found extensive layered bedrock after driving more than two miles and climbing into the "Columbia Hills."