What is a comet made of?
A comet is made of ice, dust and rock, like a dirty snowball. When it gets close to the Sun, its ice turns to gas and makes a glowing cloud and tails.
A comet is a lump of ice mixed with dust and rock, a few kilometres across. Scientists sometimes call comets 'dirty snowballs', or 'icy dirtballs', because some have more dust than ice.
The ice in a comet is not just frozen water. It also includes frozen carbon dioxide, which is dry ice, frozen carbon monoxide and other chemicals. The dust contains tiny bits of rock and carbon-rich material.
Comets spend most of their time far from the Sun, where it is extremely cold, and they look like dark, dull lumps. But when a comet comes closer to the Sun, the heat makes its ice turn straight into gas. The gas streams away, carrying dust with it. This makes a huge glowing cloud around the comet, called the coma, and long tails that point away from the Sun.
In 2014, a European spacecraft called Rosetta reached a comet called 67P and even sent a little lander, Philae, onto its surface. It found a dark, dusty, rubber-duck-shaped comet with cliffs, boulders and jets of gas.
Comet dust is what makes many meteor showers. When Earth passes through the dusty trail a comet leaves behind, we see lots of shooting stars.