Comets Essay -- essays research papers fc

The first written records of comets date back to nearly 3,000 years ago from China and Europe. The accounts of these comets were believed to be the causes of terrible events that occurred afterwards. In more recent times, however, astronomers have found out what they really are. A comet is basically a mixture of ices, from both water and frozen gases, and dust. They have also been given the names â€Å"dirty snowballs† or â€Å"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 outward; astronomers refer this to as a jet. Dust that had been mixed in with the gas is also pushed out, and as more jets appear, a small gas and dust shell forms around the nucleus, and this is called the coma. The coma, also called the head, is a dense cloud of water, carbon dioxide and other gases and comes off of the nucleus. They can be several thousand kilometers in diameter, depending on the comet’s distance from the sun and the size of the nucleus. The size of the nucleus is important because since large nuclei have a greater surface area facing the sun, which is the side that is the warmest, hence the side where most of the jets are coming from, it means more jets and greater amounts of gas and dust go into the coma. Even though the coma can get to be very large, its size can actually decrease about the time it crosses the orbit of Mars. At this distance the particles that drift out from the sun act as a powerful wind which blows the gas and dust particles away from the nucleus and coma. This is the process, wh ich makes the comet’s tail. The hydrogen cloud is very large at millions of kilometers... ...elieved that the comet Hale-Bopp was going to cause something very bad to happen, so they all committed suicide. If people can have a better understanding of what comets are, things like this could possibly be prevented. The roles that comets have played in the earth and in life as it is today are really big and important. If it had not been for comets, then life could possibly not have even existed now. Also, many creatures, for example the dinosaurs, have become extinct because of the comets colliding with the earth. If the comets had never made these creatures go extinct, then life would without a doubt be different. â€Å"Works Cited† Franklin, William. â€Å"Small Comets.† Online. Internet. Available: http://smallcomets.physics.uiowa.edu/ Hamilton, Calvin. "Asteroid Introduction." Online. Internet. Available: http://www.solarviews.com/eng/asteroid.htm Laborde, John. â€Å"Comet West.† Online. Internet. Available: http://www.solarviews.com/cap/comet/west.htm Rondlen, Michael. â€Å"Comet.† Online. Internet. Available: http://windows.ivv.nasa.gov/ Sipes, Russell. â€Å"Comet Hale-Bopp.† Online. Internet. Available: http://www.sipe.com/halebopp/"Comet Hale-Bopp"