by Jade Li

Created on: June 26, 2010   Last Updated: July 02, 2010

An Overview on Comets

For centuries comets they have fascinated and enthralled us, being the inspiration for artists, story-tellers and scientists alike. Sweeping across the sky in brilliant definition, comets are something everyone recognises.

Composition:

Composed of a mixture of ice, rock and dust, comets have often been referred to as ‘dirty snowballs’. Scientists believe comets are formed in the far regions of the Solar System at the same time the planets were forming closer in. Since they have a high concentration of ice which has not been heated significantly, they may still hold pristine amounts of the ingredients from when the Solar System was formed. Because of this, scientists are engrossed with comets since they may hold the key to where we came from and what the entire universe is actually made of.

The solid part of the comet is called the nucleus, their sizes ranging from yards to tens of miles. When a comet comes closer to the Sun, the sunlight will cause a part of the comet’s surface to convert from a solid to a gas without going through the liquid phase. This forms into a cloud which surrounds the nucleus and called the coma. The gases and particles making up this cloud are pushed outwards by solar winds and the pressure from the sunlight, which forms into tails, a breathtaking sight which comets are famous for.

The nucleus is a small part of the comet, and some coma can actually grow larger than that of the sun. There have been reports of comas being so large that they can stretch from the Sun to the Earth, 93 million miles (150 million km). The comet tails take their name from the Latin kome which means ‘hair’, and the Greek kometes, ‘a star with hair’.

Origins:

They are thought to have originated in the Oort Cloud, a region of space which astronomers have not proved actually exists but in all probability does exist. The Oort Cloud is a cloud system which surrounds our Solar System 50,000 to 100,000 times further from the Sun than what the Earth is.

Categories:

Comets are put into several different categories depending on the type of orbits they have. Every so often, some comets will get flung from the Oort Cloud and spend thousands of years travelling to our Solar System where they end up in huge orbits around the Sun. It is not sure as to why they sent to this Solar System but scientists have put forward gravitational influences of nearby star as a theory. These are known as long-period comets.

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