Temperature is very irregular in outer space. The parts that are near stars are extremely hot! Think about Venus, the second closest planet to the Sun. It goes up to 462C. But the background temperature in space is about -270C super cold! Things can change states if temperatures change so much. They can go from solid, to liquid, to gas! This is actually the reason why comets have their tails!

The tail is one of the most distinctive features of a comet!

Comets may look small from a distance, but theyre actually gigantic!

See how the Kuiper belt is disc-shaped? The Oort Cloud is farther away, so gravity from the planets dont affect it as much. Thats why it envelopes the Solar System like a sphere or a cloud!

Where the comet moves in space is important for its shape! When comets are still in the far reaches of the Oort Cloud or the Kuiper Belt, theyre made up only of their nuclei. But everything changes once they move closer to the Sun! Remember a comet is mostly made out of ice.

And what happens to ice as it gets close to heat? It melts! In the case of comets, their nuclei start to sublimate, changing from ice to gas immediately. This is when the comet starts developing its other parts!

As the ice melts, the comet gains a coma. The coma is basically a giant cloud of dust and different gases that surrounds the nucleus. Comas are extremely big up to 600,000 miles across! The coma and the nucleus make up the head of the comet. A hydrogen cloud also develops around the comets head, but we cant see it with our eyes. Hydrogen clouds are even bigger than comas they can get as big as 10 Suns!

Heres an easyway to remember what a comets head is called. The coma looks kind of like the head of a comma without its tail!

The comets tail appears when it gets close to the Sun. The tail is probably the most special feature of comets!

Asteroids are not icy like comets. Instead, theyre made out of rock and metals

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Comet Facts - Comets - Astronomy for Kids