Part 1 of Essay
The first written records of date back to nearly 3,000 years ago from China and Europe. The accounts of these 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 ....

Part 2 of Essay
.... 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; this is referred to by astronomers 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 ....