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and Jupiter .]] The asteroid belt is the region of the , 2006 . Asteroid s, or Minor Planet s, are small celestial bodies composed of rock, ice, and some metal that orbit the Sun . This region is termed the '''main belt''' when contrasted with other concentrations of minor planets, since these may also be termed asteroid belts. The asteroid belt formed from the primordial Solar Nebula as a group of Planetesimal s—the smaller precursors of the planets. However, Gravitational perturbations by Jupiter impart too much orbital energy to the bodies in this region for them to Accrete into a planet during collisions. Instead, the initial planetesimals have been broken up during the collisions, and the majority of the mass has been lost since the formation of the Solar system from this region. Asteroid orbits continue to be appreciably Perturbed whenever their period of revolution about the Sun forms an Orbital Resonance with Jupiter. At these orbital distances, a Kirkwood Gap occurs as they are swept into different orbits. The majority of the mass within the main belt is contained in the largest asteroids. The three largest asteroids in the main belt (individually named 4 Vesta , 2 Pallas and 10 Hygiea ) have mean diameters of more than 400 km, while the main belt's only Dwarf Planet , Ceres , is about 950 km in diameter. Together these four objects make up nearly half of the total mass in the belt. The remainder form a distribution of smaller bodies that range down to the size of a dust grain. The asteroid material is so-thinly distributed, however, that multiple unmanned spacecraft have traversed the belt without incident. Asteroids within the main belt are categorized by their aceous ( C-type ), Silicate ( S-type ), and Metal -rich ( M-type ). Collisions between large asteroids can form an Asteroid Family , whose members possess similar orbital characteristics and composition. Collisions also produce a fine dust that forms a major component of the Zodiacal Light . HISTORY OF OBSERVATION The Napoleonic Wars brought the first period of asteroid discovery to a close, and it would take until 1845 before another asteroid ( 5 Astraea ) was |
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