Encyclopædia Galactica Rami T. F. Rekola Tuorlan Astronomical Society Tuorla Observatory University of Turku

Asteroid (also: minor planet)

Any small body that orbits a star and is composed of rocks (silicate compounds) and metals in varying fractions. Sizes vary from centimetres to about one thousand kilometres. Orbits of asteroids are usually very elongated and/or differ considerably from the ecliptic plane.