This is a radar image of asteroid 4179 Toutatis. It's a space rock the size of a mountain, nearly three miles across at its widest point, with an estimated mass of well over five million tons. And it's headed straight for Earth. Well, nearly.
Between late Tuesday and early Wednesday morning, Toutatis will pass within about 18 lunar distances of Earth. This is uncomfortably close, as asteroids go, and Toutatis is also large enough to cause some serious problems if it ever manages to impact Earth: it's not as large as the asteroid hypothesized to have caused the extinction of the dinosaurs, but at half that size, it's still not something you'd want making a landing in your back yard.
Toutatis is currently in a big elliptical orbit that resonates with both Earth and Jupiter, and it swings by us once every four years. In 2004, it was especially close (just four times as far away as the Moon), but it's not likely you'll even notice it tonight unless you have an excellent pair of binoculars and you know exactly where to look. Despite these continuing close approaches, the probability of Toutatis actually hitting Earth in the next 600 years or so is close to zero, and doesn't go up much over the next few thousand years either. Realistically, Toutatis will probably be ejected from the solar system within just a few million years, and won't manage to make much of an impact on any planet at all.
One thing you can look forward to, though, is seeing some much better pictures of Toutatis. China is sending a 2010 lunar probe on a flyby of the asteroid on Thursday, and we should be getting some pics back that will be taken from just a few hundred miles away.
Via LA Times