They have also been given the names "dirty snowballs" or "icy mud balls." The typical comet is less than 10 kilometers across. They spend most of their time frozen solid in the outer parts of our solar system.

Comets are composed of five parts: the nucleus, coma, hydrogen cloud, dust tail, and ion tail. The nucleus is pretty solid and stable, composed mostly of ice and gas with a small amount of dust and other solids. The surface of the nucleus is best described as a black crust. Comet nuclei can range from 1 kilometer to about 50 kilometers across. The black crust on the surface of the nuclei helps the comet to absorb heat, which causes some of the ices under the crust to turn to a gas. Pressure builds up underneath the crust and causes the surface to bubble up in some places. Eventually, the weak spots of the crust break open from the pressure, and the gas shoots ou

tward; astronomers refer this to as a jet.

Hydrogen was discovered in comets Tago-Sato-Kosaka and Bennett. It is ionized hydrogen that forms the light that goes past the coma. The reason why the hydrogen cloud was not discovered for a long time is because it is not visible from Earth. Atomic hydrogen emits in the ultraviolet, but the ozone layer stops the waves from entering. The hydrogen cloud can only be observed from space, with satellites. The dust tail is usually up to 10 million kilometers long, and is composed of smoke-sized dust particles that come off the nucleus by escaping gases. The dust tail is also the most visible part of a comet to the naked eye. The tail has a potential to be long when it enters the orbit of Earth. The record for the longest tail is the length of the Great Comet of 1843; its tail extended more than 250 million kilometers. The ion tail, known as type I or plasma, is made up of ions. It can be up to 100 million kilometers long and 100,000 kilometers wide. The tail is straight and always is opposed to the direction of the Sun. The color of it, through a spectrum, is mostly blue. The reason why the tail is ionized is because of solar wind. Solar wind, which flows at about 400 kilometers per second, is filled with charged particles that are around the solar magnetic field. The gases in the tail are ionized by the process of "photo ionization of the neutral molecules under the action of the solar ultraviolet radiation", or "under the action of the solar wind by a phenomenon where a proton removes an electron from an atom." The speed at which the ions are moving is what causes the tail to be straight. The light from the tail is emitted by "fluorescence," which is a particle of solar wind that excites an electron of the atom or molecule concerned. This electron reaches a level at which it is stable, goes down again and releases its energy in the form of a photon, a particle of light, of a well determined energy and thus, of a specific color.

When our solar system began, it was just a vast cloud of gas and dust. Several billion years ago, the cloud slowly rotated around the sun, which was very young, and particles within the cloud collided with one each other. During this time some objects were shattered by these collisions, while others grew in size and were to later become the planets. Throughout this early period, comets probably filled the solar system. Their collisions with the early planets played a major part in the growth and evolution of each of the planets.

Hamilton, Calvin. "Asteroid Introduction." Online. Internet. Available:

Franklin, William. "Small Comets." Online. Internet. Available:

http://www.sipe.com/halebopp/"Comet Hale-Bopp"

Some common words found in the essay are:
Earth Atomic, China Europe, Collisions Earth, Kea Hawaii, Oort Cloud, Seeing Oort's, Jupiter Comets, Heaven's Gate, Halley's Comet, Comet Grigg-Skjellerup, solar system, kuiper belt, online internet available, internet available, solar wind, online internet, hydrogen cloud, gas dust, halley's comet, dust tail, kilometers diameter, outside solar system, dust particles nucleus,
Approximate Word count = 2365
Approximate Pages = 9 (250 words per page double spaced)