Spirit, also known as MER-A, is a robotic rover on Mars, active from 2004 to 2010. It landed successfully within the impact crater Gusev on Mars at 04:35 Ground UTC on January 4, 2004, three weeks before its twin, Opportunity (MER-B), which landed on the other side of the planet. The rover became stuck in a "sand trap" in late 2009 at an angle that hampered recharging of its batteries; its last communication with Earth was sent on March 22, 2010.