A comet is a very small solar system body made mostly of ices mixed with smaller amounts of dust and rock. Most comets are no larger than a few kilometres across. The main body of the comet is called the nucleus, and it can contain water, methane, nitrogen and other ices.
When a comet is heated by the Sun, its ices begin to sublimate (similar to the way dry ice “fizzes” when you leave it in sunlight). The mixture of ice crystals and dust blows away from the comet nucleus in the solar wind, creating a pair of tails. The dust tail is what we normally see when we view comets from Earth.
Sometimes comets are referred to as “dirty snowballs” or “cosmic snowballs”. This is because they are composed mostly of ice, rock, gas and dust.
- A comet has four components: a nucleus, a coma, a dust tail and an ion tail.
- Comets are believed to originate in one of two regions – the theorized Oort Cloud, or the Kuiper Belt found beyond the orbit of Neptune and the dwarf planet Pluto.
- The most famous comet is Halley’s Comet. It has been observed since at least 240 B.C. Its orbit makes it visible from Earth every 76 years. It was named after the British astronomer Edmond Halley.
- Notable comets include Comet Hale-Bopp, which was discovered in 1995 and Comet Hyakutake, discovered in 1996.
- There are over 3,000 currently known comets. Scientists believe that there be up to one billion comets in our solar system.
- A great comet is one which is bright enough to be visible from Earth without the need for a telescope. Approximately one great comet happens every ten years.
Image Credit: www.space.com