Scientists analysing the surface of a giant asteroid are puzzling over bright spots that represent some of the purest materials seen so far by a Nasa spacecraft.
Nasa released new images of the asteroid Vesta taken by the orbiting Dawn spacecraft that show some places on the surface twice as bright as others.
The bright material, found mostly around craters, appeared as a result of rocks slamming into the surface and exposing it.
Researchers are still trying to determine what it is made of but believe it is pristine and unchanged from the asteroid's formation some four billion years ago.
Dawn has been studying Vesta since it entered orbit last year. The spacecraft is set to depart Vesta this summer and cruise to another asteroid, Ceres, arriving in 2015.