WHAT IS A COMET?

A comet is a small space object made up mostly of ice mixed with 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. The nucleus can be as small as a few metres or as large as a few kilometres across.

When a comet is heated by the sun, its ice begins to sublimate; this means it goes directly from being ice to being gas without melting (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 see a comet from Earth.

Facts about comets:

• Material coming from a comet becomes part of the comet’s orbit in a stream. If Earth (or another planet) moves through that stream, those particles fall into Earth as meteor showers.

• Comet orbits are usually elliptical.

• Comets are not spaceships or alien bases. They are fascinating bits of the solar system material that date back to the formation of the sun and planets.