Asteroid

Astronomical Dictionary

(Also "planetoid") These are rocky bodies, the vast majority of which orbit the Sun between Mars and Jupiter. It is thought that there must be around 100,000 in all. The largest asteroid is Ceres which has a diameter of 579 miles. The smallest detected asteroids have diameters of several hundred feet. Together with comets and meteoroids, asteroids make up the minor bodies of the solar system. They are considered to be left over planetesimals from the formation of our solar system. The gravitational pull of Jupiter is thought to have stopped the members of the asteroid belt from forming a planet. Most asteroids orbit the Sun in a belt between Mars and Jupiter between 2.2 and 3.2 au. 4,000-odd asteroids have been formally numbered and named. The average eccentricity of their orbit is .15 and their average orbital inclination about 10?. There are millions of asteroids, most of them in a belt of such bodies orbiting between Mars and Jupiter. The outermost asteroid was thought to be Chiron with a 51-year orbital period until asteroid 1992AD was noted (on January 9, 1992 by David L. Rabinowitz) with a period 93 years, perihelion at approximately 8.7 au, aphelion at 32 au (extending far enough to cross the orbits of Saturn, Uranus, and Neptune), a maximum inclination to the ecliptic of 25?, and magnitude 17.

 
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