Enhanced-colour image of asteroid 951 Gaspra, taken by the Galileo spacecraft on 29 October 1991 at a distance of 16,200km. Three images, taken through violet, green and infrared filters, have been enhanced to exaggerate colour differences, then superimposed on a high-resolution (54 metres per pixel) monochrome image. Bluish areas are probably regions of the mineral olivine. The reddish material is thought to be the outer layer of rock (regolith), with the blue olivine having been exposed during cratering events. Gaspra is approximately 19km x12kmx11km in size and orbits the Sun at the inner edge of the main asteroid belt between Mars and Jupiter.