comet
comet Small, icy Solar System body in orbit around the Sun. The solid nucleus of a comet is small, that of Halley's comet measures just 16 × 8km (10 × 5mi), and comprises rock and dust particles embedded in ice. As the comet approaches the Sun, evaporation begins, and jets of gas and dust form the luminous coma. Later, radiation pressure from the Sun and solar wind may send dust and gas streaming away as a tail, as much as 150 million km in length. There are three main types of comet: short-period comets often have their aphelia at approximately the distance of Jupiter's orbit. Long-period comets have aphelia near or beyond Neptune's orbit. The third type are either called non-periodic, or hyperbolic. Their periods may be as much as several million yaers. See also meteor
More From encyclopedia.com
NEARBY TERMS
comet