Comets

Comets are large balls of ice, rock and dust. They are sometimes called "Dirty Snowballs".

They have very elliptical orbits, which means that they do not go around the Sun in a simple circle, but in a long, stretched out path.

At their furthest point they are much further away from the Sun than Pluto, but at their closest, they can be closer than Mercury.

For most of the time they are invisible, but as they get closer to the Sun, the ice starts to heat up and turn into gas.

This is blown backwards by the light from the Sun and makes an enormous tail that stretches out behind the comet.