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Solar System

Asteroids

The double asteroid, 90 AntiopeThe double asteroid, 90 AntiopeCircling the Sun between the orbits of Mars and Jupiter are millions of small, planet-like objects called asteroids or minor planets (sometimes also called planetoids). The largest, Ceres, discovered in 1801—and, since 2006, upgraded to the status of "dwarf planet"—measures just over 1000 kilometres (600 miles) across, but only a few asteroids (around 200) have diameters greater than 100 kilometres (60 miles). It is thought there may be at least a million objects with a diameter of 1 kilometre or more. About 800,000 asteroids have so far been discovered, of which about 22,000 have been named. Many more are tiny specks too small to be identified. 

A close-up view of a typical asteroidA close-up view of a typical asteroid
Plan view of the asteroid beltPlan view of the asteroid belt

Orbital paths

Most asteroids lie in bands between Mars and Jupiter, although some have strayed far from here. The Trojan asteroids, for example, share Jupiter’s orbital path, while Apollo, Icarus and Adonis actually pass inside Earth’s orbit. In fact, more than 7000 near-Earth asteroids have been identified, of which more than 500 are estimated to measure over 1 kilometre (0.6 miles) in diameter.

The name asteroid, originally proposed by German-born British astronomer Sir William Herschel, is from the Greek asteroeides, meaning "star-shaped".

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