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Comets are big chunks of ice, rock and gas. They are dirty snowballs of leftovers from the beginning of our solar system. Comets get their name from the Greek word "kometes" (long hair) - a reference to their tails.

Comets are mysterious. Scientists think they might be able to tell us about the origins of our solar system.

A few comets close enough for us to see from Earth. They probably come from an area around Pluto called the Kuiper Belt. When Earth passes through the tail of a comet, we see a meteor shower.

WHAT'S IT LIKE ON A COMET?
Unless you could travel way out beyond Pluto, it would be hard to stand or land on a comet. When comets get close to the Sun, they begin spewing gas and dust. The debris form the head - or coma - and a tail. The tail always points away from the Sun. The only solid part is the nucleus in the middle.

If you did manage to land on a comet, you might end up getting blasted into space on a jet of gas and rock. Or, if your comet got too close to the Sun, it would break up completely. Gravity is so light you would feel like a feather.

Spacecraft that visit comets have to be tough. The rocks and debris in the tail can cause a lot of damage. In the next few years, scientists will use super tough spacecraft to catch pieces of a comet's tail and blast a football-field size hole in another comet to see what's inside the nucleus.

Want to learn more? Explore asteroids in depth at NASA's Solar System Exploration website.

COMET CHALLENGE As a comet approaches the sun, does its head or tail lead the way? What about when it starts traveling away from the Sun? Hint: The answer is on this page.

Missions to Comets Featured Mission: Stardust Stardust will use a super light substance called Aerogel to capture pieces of the tail of a comet and return them to Earth. More Missions to Comets Past Missions Present Missions