Astronomy Picture of the Day

Explanation: You're zipping through the Solar System when you pass ... asteroid 253 Mathilde. This actually happened to NASA's NEAR spacecraft just last Friday. The above picture of the previously unresolved asteroid was released just yesterday. Mathilde's large craters and irregular shape indicates that it has undergone huge collisions with other large space rocks in the past. Mathilde has more large craters than asteroids 243 Ida and 951 Gaspra, which were photographed by the Galileo spacecraft now orbiting Jupiter. In the image centre is a crater over 20 kilometres across. Asteroids are rare enough so that spacecraft traveling through even the main asteroid belt need not fear colliding with any - let alone one as large as Mathilde.