What Is A Comet?

A comet is a small, icy body that goes around the Sun in our Solar System. It travels on an elliptical path that occasionally brings it within sight of the Earth. A famous comet is Halley's comet, which passes near to Earth every few hundred years.

A typical comet consists of a central nucleus that measures a few kilometres across. It is a bit like a dirty snowball because it contains just ice and dust. A the comet gets nearer to the Sun, its nucleus heats up and this boils the water in the ice and gas and dust are released to form the ball of the comet, more properly known as the coma. This can form up to 60 000 miles across around the nucleus. Gas and dust streams away from the coma to form one or more tails that can be millions of miles long.

Comets are thought to have originated at the same time as the Solar System. There may be millions of them in the Oort cloud, the huge halo that lies just off the planet Pluto at the edge of the Solar system. Periodic comets like Halley's comet are thought to come from the Kuiper belt, a zone just beyond Neptune. Encke's comet, the most regular of the periodic comets, orbits the Sun every 3.3 years.

A comet is a small celestial body consisting mostly of dust and gases that moves in an elongated elliptical or nearly parabolic orbit around the sun.