Goals: Spirit and its twin Opportunity were designed to study the history of climate and water at sites on Mars where conditions may once have been favorable to life. Each rover is equipped with a suite of science instruments to read the geologic record at each site, to investigate what role water played there and to determine how suitable the conditions would have been for life. The rovers are solar powered, but their mission has been enabled by the use of radioisotope heater units.
Accomplishments: Both rovers far exceeded their design specifications and returned science results that transformed our understanding of Mars. Both rovers discovered strong evidence for liquid water on Mars in the distant past.
Spirit uncovered strong evidence that Mars was much wetter than it is now in a silica patch apparently produced by hot springs or steam vents.
Opportunity has returned dramatic evidence that its area of Mars stayed wet for an extended period of time long ago, with conditions that could have been suitable for sustaining microbial life. Opportunity also has analyzed exposed rock layers recording how environmental conditions changed over time.
A view from Mars Exploration Rover Opportunity shows layered deposits in the wall of an impact crater. Studying layered deposits like these can help reveal the ancient history and climate of Mars.
Mars Exploration Rover Spirit captured this stunning view as the Sun sank below the rim of Gusev crater on Mars. Such images help scientists to determine how high into the atmosphere the martian dust extends, and to look for dust or ice clouds.