Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2000 August 29 The Regolith of Asteroid Eros Credit: NEAR Project, JHU APL, NASA

Explanation: From fifty kilometres above asteroid Eros, the surface inside one of its largest craters appears covered with an unusual substance: regolith. The thickness and composition of the surface dust that is regolith remains a topic of much research. Much of the regolith on 433 Eros was probably created by numerous small impacts during its long history. In this representative-colour view taken by the robot spacecraft NEAR-SHOEMAKER currently orbiting Eros, brown areas indicate regolith that has been chemically altered by exposure to the solar wind during micrometeorite impacts. White areas are thought to have undergone relatively less exposure. The boulders visible inside the crater appear brown, indicating either that they are old enough to have a surface itself tanned by the solar wind, or that they have somehow become covered with some dark surface regolith.