What is an Asteroid

Ceres

Asteroid 1 Ceres, the largest body in the asteroid belt. Image:Nasa

Asteroids are small rocky bodies that generally have irregular shapes and lack the active characteristics which are a feature of comets when they pass within the inner solar system. The largest concentration of asteroids is found in the zone between the orbits of Mars and Jupiter termed the asteroid belt. Asteroid 1 Ceres, the largest body in the asteroid belt, has a diameter of approximately 945 km and is the only object in the belt that is rounded by its own gravity. It is estimated that Ceres represents close to one third of the mass within the asteroid belt. Asteroid 4 Vesta, the second most massive asteroid, was studied in detail by the NASA Dawn mission prior to its departure to study Ceres, which it is presently undertaking. Vesta is generally considered to be the source of the important HED group of meteorites.

VESTA

Asteroid 4 Vesta the second most massive object in the asteroid belt. Image: NASA

Asteroids are small rocky bodies  that  generally have irregular shapes and lack the active characteristics which are a feature of comets when they pass within the inner solar system. The largest concentration of asteroids is found in the zone between the orbits of Mars and Jupiter, which is generally referred to as the asteroid belt. Ceres, by far the largest body in the asteroid belt, is not technically an asteroid 

951_Gaspra

Asteroid 951 Gaspra is an S-type asteroid and a member of the Flora asteroid family. It has an average diameter 12km. This picture of Gaspra is a combination of the highest-resolution images and colour information obtained by the Galileo spacecraft. The Sun is shining from the right. The subtle colour variations on Gaspra’s surface have been exaggerated. Albedo and color variations are associated with surface topography The bluish areas are regions of slightly higher albedo and tend to be associated with some of the crisper craters and with ridges. The slightly reddish areas, apparently concentrated in low areas, represent regions of somewhat lower albedo. In general, such patterns can be explained in terms of greater exposure of fresher rock in the brighter bluish areas and the accumulation of some regolith materials in the darker reddish areas. Caption and image: NASA

253 Mathilde

253 Mathilde is a C-type asteroid with an approximate diameter of 50 km. Image: NASA