Most comets and asteroids are small enough for their internal forces to withstand the deforming forces of gravity. As a result, some of them are highly irregularly shaped, as revealed by the images and radar maps available. The planetary sized satellites of the giant planets are essentially spherical, but the shapes become increasingly more irregular when moving to the smaller moons. The range of lightcurve amplitudes in the asteroid population indicates a variety of shapes from almost spherical to highly elongated.
The shape is a historical record of impacts, catastrophic collisions, geological activity, cometary activity, or perhaps even the accretion of planetesimals in the early days of the solar system. The shape is also an important issue when comparing the distributions of mass, density, composition, and angular momentum between various populations of objects.
The shapes of minor bodies in the solar system are, however, difficult to investigate. There are space mission fly-by images of a few objects. Some near-Earth asteroids have been mapped by radar techniques. Most asteroid shapes, however, are currently only available as low order estimates from visual light curve investigations.
The Uppsala planetary system group
Johan Lagerros