Comets and Asteroids

As well as the sun, the planets and their moons, our solar system contains comets and asteroids.

Asteroids are just very large rocks, held in a regular orbit around the sun by gravity. There are thousands of asteroids in a 'belt' between Mars and Jupiter. These might be the remains of a planet that didn't form properly, or that exploded for some reason. Scientists think that the strong gravity from Jupiter might have prevented these rocks from joining to become a planet in the very early days of the solar system.

There are also millions (maybe billions) of asteroids in the Kuiper Belt, which extends beyond Neptune. Outside the Kuiper Belt is the Oort Cloud, which is where most comets seem to come from.

Comets are lumps of rocks, dust and ice that come from the Oort Cloud, or somewhere else very far away in the solar system. Comets have an oval shaped orbit, meaning that they come right up close to the sun and then they fly far away again.

When a comet is near the sun the comets surface starts to evaporate and it releases gas and dust, which becomes the tail. Comets actually have 2 tails, one made of dust and the other from gas.

The most famous comet is Halley's comet, which last passed by Earth in 1985-1986. Another famous comet is Shoemaker-Levy, which was photographed smashing into Jupiter in 1994. There is also massive comet called Hale-Bopp that will pass Earth again in the 44th century.

The Kuiper Belt and the Oort Cloud	Comet Shoemaker-Levy smashing into Jupiter.	Inside Halley's comet.
The Kuiper Belt and the Oort Cloud	Comet Hyakatuke	Comet Hale-Bopp