They are very small bodies, not usually any bigger than 10 km or so. Despite their very small size, they create huge spectacles when they get close enough to the Sun to release water from their surface. This water escapes immediately into space and usually carries some dust or dirt along with it. This material leaves huge tails and streamers in the sky. Some of the known asteroids wander in as far as Venus or Mercury and a new batch has recently been recognized out well beyond the orbit of Pluto.
Asteroids are small, irregularly shaped objects, that have inert and airless surfaces.
Satellite This class of object is perhaps the simplest. If the object orbits another larger object, then it is considered a satellite. These bodies can, and do, span a great range of sizes and properties including those shared by all the other categories. Planet A planet is a special term applied to the larger members of our solar system. There are certain properties we expect to see in a planet such as an atmosphere and dynamic and active surfaces at some stage in their history.