Illustration entitled 'Chiron Approaching the Sun'. Discovered in 1977, Chiron is one of the larger minor planets (asteroids) that orbit the Sun. Its orbit is unusual in that it lies almost entirely outside that of Saturn, varying from 1,273 million km and 2,824 million km during its 50.7-year orbital period. Chiron is about 300km in diameter, and is thought to be an escaped moon of one of the outer planets. Some astronomers view Chiron as the first member of an outer belt of minor planets, although others have yet to be identified.