Spirit, also known as MER-A (Mars Exploration Rover – A) or MER-2, is a robotic rover on Mars, active from 2004 to 2010. It was one of two rovers of NASA's Mars Exploration Rover Mission. 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. Its name was chosen through a NASA-sponsored student essay competition. 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.