Now operating three times longer than originally expected, NASA’s Mars Exploration Rovers are still turning up fresh evidence that liquid water once flowed on Mars. Opportunity has found a rock, dubbed “Escher”, which has a network of cracks similar to cracked mud when the water has dried up. On the other side of Mars, Spirit is still climbing up the “Columbia Hills”, and it seems that every rock it looks at shows evidence that it was altered by water. “We haven’t seen a single unaltered volcanic rock, since we crossed the boundary from the plains into the hills, and I’m beginning to suspect we never will,” said principal investigator Dr. Steve Squyres.