For centuries, man has viewed comets with awe, even with fear. Comets are one of the most amazing phenomena to be seen in the sky. Often, comets have induced fear of possible portending doom. Halley’s Comet, a famous comet that travels around our sun every 76 years, was once thought to bring an omen to Earth. In 1910, Earth passed through the tail of Halley’s Comet with no ill effects. Other stories about comets are the Babylonian “Epic of Gilgamesh”, thousands of years old, associated destruction with arrival of a comet. Comets have been blamed for the Great Flood. This negative view of comets existed in Rome, Mongolia, and other places. Romans associated a comet with the death of Julius Caesar. Incas cited a comet to their conquest by Pizarro.
Comets consist of a head, a coma, a nucleus, jets, and a tail. The tail is the long part of a comet, which can be millions of miles long. Inside the head is the nucleus, which may be only a few miles in diameter. Surrounding the nucleus is a much larger spherical region which can be as large as the sun itself. This is called the coma. The nucleus sometimes emits streams of material. These jets or streams directed away from the comet’s nucleus, look like beams or rays of light.
How does science explain the origin of comets? Where did they come from? How did they originate? There explanation to these questions is this. The Oort Cloud. The Oort Cloud named for Dutch astronomer Jan Oort, is a hypothesized collection of ice balls formed from interstellar dust reaching as far as 1,000 times the distance of Pluto from the sun. So according to the Oort Cloud view, there are comets out there, or pre-comets, or proto-comets, that may get knocked loose at times and fall toward the sun, thus forming what we today call a comet. The problem with the Oort Cloud hypothesis is it does not work because of the minerals found in comets that require much higher temperatures than these of the Oort Cloud and because of minerals that require liquid water to form while there cannot be liquid water in the Oort Cloud.
Science today obviously does not completely understand comets. Donald Brownlee, Principle Investigator, The Stardust Mission said, “Its a mystery to me how comets work at all.” They have found in comets minerals that require liquid water to form, yet liquid water cannot exist in the cold regions of space where comets supposedly form. Dante Lauretta, an associate professor of cosmochemistry and planet formation at the UA’s Lunar and Planetary Laboratory said, “Current thinking suggests that it is impossible to form liquid water inside of a comet.” Lauretta is the principal investigator of the UA team involved in analysis of samples returned by NASA’s Stardust Mission.