Accessentertainment IndexAstronomy Index

Asteroids are celestial objects that generally orbit the Sun in a belt between Mars and Jupiter. They are rocky in nature and have irregular shapes. The size of asteroids vary greatly from less than 1 metre upto about 1000 km. Most of the asteroids in the main belt can be seen to come from larger bodies that broke up 1000`s million years ago and spread out into what exists today. It is thought by some scientists that the asteroids were in fact another planet that was destroyed in a cataclysmic event early on in the life of the solar system.

Not all asteroids orbit the sun in the main belt, the most well known of these orbit the Sun at the same distance as Jupiter. There are some leading Jupiter and some following. They are collectively known as the Trojans.

Some asteroids are rogue in nature and orbit the Sun at many different distances and can have circular or elongated orbits. Some of these asteroids cross the Earths orbit, but it is most unlikely that we will see one hit the Earth in our lifetime. In fact it is unlikely the Earth will be hit be a large asteroid for millions of years.

Comets are different in nature to asteroids. They are generally made of dust and ice and have very long orbital paths that can take 100`s of years to be completed. They generally have very elongated paths that can bring them within Mercury`s orbit at the closest point of their approach. When the comet is close enough to the Sun the ice melts and the gas and dust is forced into trails. The gas is directly behind the comet with relation to the Sun, and the dust trail is to the side. A diagram is shown below of this relationship.

The dust follows the orbit from where it breaks of and so the trail appears to be a large curve.

Most Comets are thought to reside in the Oort Cloud which is far beyond the orbit of Pluto. Occasionally a comet will get pushed out of its orbit in this Oort cloud and this is when they become visible to us. The Oort cloud is so far out that it is possible a passing star can disturb the comets. However it is not thought any stars have done this feat for many millions of years.