Perched on the rim of an ancient 22,000 meter-wide crater, the Mars rover Opportunity has reached a new type of rock that scientists believe may contain evidence that the planet was once capable of sustaining life. Washington University professor Raymond E. Arvidson is the mission’s deputy principal coordinator.

Two Mars rovers, Opportunity and Spirit, recently found signs of water that ran beneath the planet’s surface in the distant past. Both rovers are directed through the Earth and Planetary Remote Sensing Laboratory at Washington University.

The Mars Exploration Rovers, Spirit and Opportunity, launched in the summer of 2003. Now, more than six years later, the two robot geologists are still running and collecting data on Mars, though their missions were expected originally to last only 90 days each.