Despite a temporary loss of communication with the "Spirit" rover (caused by a file system anomaly [http://www.cs.princeton.edu/courses/archive/fall11/cos109/mars.rover.pdf]) delaying exploration for several days, both rovers eventually began exploring their landing sites. The rover "Opportunity" landed in a particularly interesting spot, a crater with bedrock outcroppings. In fast succession, mission team members announced on 2 March that data returned from the rover showed that these rocks were once "drenched in water", and on 23 March that it was concluded that they were laid down underwater in a salty sea. This represented the first strong direct evidence for liquid water on Mars at some time in the past.