Astronomy Picture of the Day

Explanation: On Wednesday, September 29, the Earth came within one million miles of the asteroid Toutatis -- the closest predicted aproach of our fair planet to a sizable asteroid or comet in this century. Coming within one million miles or about 4 times the Earth-Moon distance, Earth would appear to be nearly the size of the full moon in the asteroid's sky, as suggested in this illustration. In Earth's sky, Toutatis appeared only as a faint object rapidly moving against a background of stars. Also known as Earth-crossing asteroid 4179, Toutatis is in an eccentric 4 year orbit which moves it from the asteroid belt between Mars and Jupiter to just inside Earth's orbit. When the Earth passed near it in 1992 Toutatis was imaged by radar and seen to be two irregularly shaped lumps, perhaps joined by a narrow neck. This bizarre object is up to 1.5 miles wide, 3 miles long, and is tumbling through space. Studies of Toutatis and other Earth-crossing asteroids help reveal connections between the Solar System's meteorites, main-belt asteroids and comets. These asteroids also offer tantalizing targets for robotic exploration and, over time, represent potential collision hazards for planet Earth!