4

S A T U R D A Y

Thirty years ago, Mariner 4 whizzed by Mars and shattered the dreams of science-fiction fans everywhere. Its photographs showed no canals or crystalline cities—just a vast expanse of barren, heavily pockmarked terrain. Was the red planet always so desolate? In “Early Mars,” planetary geologist Robert Craddock discusses what may have happened to the water on Mars, and whether it sloshed around long enough to spawn some primitive microbial life. At 9:30 a.m. at the National Air & Space Museum’s Einstein Planetarium, 6th & Independence Ave. SW. FREE. (202) 357-2700. (Greg Kitsock)