NASA’s Curiosity rover has found a series of symmetrical, 10-m- (33-foot-) high gravel ridges — sedimentologic evidence of ancient giant floods — in Gale Crater on Mars. This artist’s impression shows how Mars may have looked about 4 billion years ago. Image credit: M. Kornmesser / ESO. “We identified megafloods for the first time using detailed sedimentological data observed by the rover Curiosity,” said Dr. Alberto G. Fairén,...