More than four years after its expected demise, the Mars rover Opportunity continues to send back valuable data as it crawls across the planet's surface.
In a new study, researchers analyzing that data have found evidence that an entire Oklahoma-sized region of Mars called the Meridiani planum was shaped by years of wind and water flows.
The first geologist on Mars isn't human, but a 380-pound automaton called Spirit. View a NASA animation of Spirit's journey from launching pad to Mars, and learn about the instruments on the robotic explorer.