Shortly after the launch of Mars Express, NASA sent a pair of twin rovers toward the planet as part of the "Mars Exploration Rover" mission. On 10 June 2003, NASA's "MER-A" "(Spirit)" Mars Exploration Rover was launched. It successfully landed in Gusev Crater (believed once to have been a crater lake) on 3 January 2004. It examined rock and soil for evidence of the area's history of water. On 7 July 2003, a second rover, "MER-B" "(Opportunity)" was launched. It landed on 24 January 2004 in Meridiani Planum (where there are large deposits of hematite, indicating the presence of past water) to carry out similar geological work.