Astronomy Picture of the Day

Explanation: Asteroid 433 Eros is posing several riddles. NASA's robot spacecraft NEAR began orbiting the 30-kilometer space rock last week, and new pictures are now being beamed back to Earth regularly. As usual in science, when you arrive at a place you've never been before, you see things you don't immediately understand. Scientists are contemplating, for example, the cause of the above-pictured giant gouge in the middle of Eros. Intriguing internal features include groves oriented parallel to the asteroid's length and the relative paucity of craters. These indicate that the gouge formed well after the asteroid itself. One question answered by the shape and density is that, unlike asteroid 253 Mathilde, Eros is not a pile of rocks but one big rock. Astronomers are hopeful that data taken over the coming year might indicate the nature and origin of the baffling bright patches.