The mission of Mars Exploration Rovers is to find the history of water and evidence of past life on the fourth planet from the sun. The U.S. National Aeronautic and Space Administration calls the rovers "robot geologists." NASA launched two rovers separately in June and July 2003, and they landed on January 3 and 24, 2004. NASA sent another rover, Curiosity, in 2012 to determine whether Mars could ever have had life; Curiosity found water and organic molecules in 2014.
The robots launched in 2003 were exploring opposite sides of Mars that may have once had liquid water. One rover was sent to Gusey Crater, an impact crater in which a lake may have formed at one time. The other went to the Meridiani Planum, where the presence of the mineral hematite indicates a possible wet past. The rover robots search for and categorize soils and rocks to give NASA scientists clues about any past presence and activity of water. One of the rovers, Spirit, was silent as of fall 2015.
The goal was for the two original rovers to travel about 44 yards in day for a total of 3/4 a mile, a goal that has been exceeded by far. The rovers perform geological explorations as they move about. Cameras mounted on 5-feet-tall masts give a 360-degree view of the landscape. Other tools include spectrometers for analyzing iron and other elements in soils and rocks, magnets to collect magnetic dust particles, a microscopic imager that can capture high-resolution images of soils and rocks, and a rock abrasion tool to remove surfaces of rocks and expose material for further examination.
NASA designed Curiosity to travel 98 feet per hour. It also carries instruments to examine rocks and soil and determine Mars' past environment.