The Mars Exploration Rover mission, also known as MERS, is the second mission sent to Mars that involved rovers. MERS aims to study Mars surface looking for clues about the past water activity on Mars. This information is vital to accomplish one of the goals of the mission: to find out whether life ever existed in Mars.
To do so, twin rovers, Opportunity and Spirit, were sent to different locations on opposite sides on Mars that were apparently affected by liquid water in the past, the Gusev Crater and Meridiani Planum.
Spirit was launched on June 10, 2003 and arrived to Mars on January 4, 2004, and Opportunity was launched on July 7, 2003 and arrived on January 25, 2004.
