NASA's Stardust spacecraft snapped these photos of Comet Wild 2 on January 2, 2004. On the left is the comet nucleus and on the right a composite of the nucleus and a longer exposure highlighting the comet's jets. According to a recent press release, project scientists expected "a dirty, black, fluffy snowball" with a couple of jets that would be "dispersed into a halo". Instead they found more than two dozen jets that "remained intact"-they did not disperse in the fashion of a gas in a vacuum. Some of the jets emanated from the dark unheated side of the comet-an...