NASA's Curiosity rover has discovered its first evidence that water was flowing on Mars in the planet's ancient history. Several pieces of evidence were found, and scientists believe water was once vigorously flowing in the Gale crater area for perhaps thousands or millions of years, but it would likely be billions of years in the past. Full details at Wired.
Along with material seen at the Goulburn scar, which was uncovered when Curiosity’s lander rockets disturbed the ground, these rocks add up to a picture of an ancient stream bed that once flowed through this area. Judging from the size of the gravel that was carried, scientists estimate that water likely ran at a steady two miles per hour and came to about ankle or hip height.