Spirit and Opportunity are identical twin robotic rovers that have gone far beyond their original scientific
objectives to rewrite our understanding of the early history of Mars. NASA sent these two “robotic geologists”
on a 90-day mission to search for geological clues
regarding environmental conditions on early Mars, and
assess whether those environments were conducive to
life. The mission team chose two landing sites, Gusev
Crater and Meridiani Planum, for the likelihood that
liquid water, a prerequisite for life, was once present
there.