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Biology 103
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Bopped by Hale-Bopp

Sarah Sterling

On July 23, 1995 two different men sat in two different states. Each gazed up at the same night sky: one from a desert and one from his home. They peered through their telescopes and saw something they hadn't seen before. A faint glow caught their eyes in the Messier 70 (M70), part of the Sagittarius constellation. Each of these amateur astronomers tracked this object for hours and then reported the sighting of what would later be known as Comet Hale-Bopp(1).

Comet Hale-Bopp, discovered by Alan Hale of New Mexico and Thomas Bopp of Arizona, remains the farthest comet ever discovered by amateurs(10). It is made up of a nucleus consisting of dust, rock and ice (like most comets), also known as a 'dirty snowball' (8)., and orbits the sun at a rate of 11.4 hours(1). As Hale-Bopp moved closer to the sun the ice of the nucleus sublimated (turned from a solid into a gas without passing through the liquid state) and created a steam-like coma. In the case of a comet, a coma is the atmosphere surrounding the nucleus. This sublimation also creates the comet's two tails which stream away from the sun and are visible due to the reflection of the sun off of the dust particles(2).

The Hubble Space Telescope recorded the comet nucleus to have a diameter of approximately 40km or 25 miles(1). In whole, Comet Hale-Bopp is 2 million kilometers in size! (8). It is both extremely large and extremely bright, not to mention the most visible comet to be seen by the naked eye since 1977(1). At the time of its discovery, Comet Hale-Bopp was 666 million miles from the sun. It reached its closest point to the earth (122 million miles away) around March 22, 1997, and is possibly the most viewed comet ever(2).

There are many controversies surrounding Comet Hale-Bopp. One popular controversy is the argument of whether or not Hale-Bopp has a satellite. Images from the Hubble Space Telescope have some convinced that the subtle gravitational pull from the comet could have sucked a satellite into orbit around it. Zdenek Sekanina, a journalist in the Jet Propulsion Lab at Earth, Moon and Planets magazine, believes that Hale-Bopp is a "prime candidate" for a satellite. Others believe that these images are not enough to prove the existence of a satellite and note that though some comets have had satellites, the possibility is doubtful(9).

The second controversy involves the discovery of the comet's third tail in April of 1997. According to Dr. Don Pollaco of the Isaac Newton Group, the new type of comet tail that follows Hale-Bopp is a "straight tail of sodium atoms six degrees long". This third tail is more defined than the normal ion tail and runs in a completely different direction. The Isaac Newton Group reports that this sodium tail is about 600,000 km wide and 50 million km long. This third tail is controversial due to the fact that no one is sure how the tail is formed. Nothing like this has ever been seen before, but more sodium ions were detected in great amounts in and around Hale-Bopp. This leads scientists to ponder the circumstances and area where the creation of this comet took place(3).

So how and where are comets normally formed? Scientists used to believe that comets formed from a cloud of dust and gas existing in space prior to planets(4). This belief is a result of a theory developed by Dutch astronomer Jan Oort. His theory basically says that far out in the solar system is the debris left over from its formation. This debris, which consists of tiny particles of dust and ice, crashes into each other and sticks together, forming large chunks of debris miles across. Many of the chunks create an enormous cloud (Oort Cloud), which looks a lot like a giant bubble surrounding our solar system really far away. Stars moving through this cloud can cause enough of a disturbance to send chunks flying into the inner solar system, also known as a comet(6).

A new study of Comet Hale-Bopp shows that they may be formed differently. A comet's tail glows in different colors depending on the chemicals that make it up. Scientists discovered that by using infrared technology on Hale-Bopp, they were able to measure the amounts of Carbon Monoxide emitted. The results have led some to believe that this comet formed somewhere between Jupiter and Neptune. Catholic University and NASA's Goddard Space Flight Center specialist, Michael DisSanti says, "The amount of Carbon Monoxide ice compared to water indicates that [Hale-Bopp] formed somewhere between the orbits of Jupiter and Neptune. We hope to learn more about what was going on when the giant planets formed by investigating the chemistry of this comet". Knowing that an Oort Cloud does exist leads these scientists to further their theory into one which says that after these comets are formed it is the gravity of the larger planets that first sends them to a "cold storage" - the Oort Cloud(4).

Either way, the existence of comets dates back to times long before the existence of people. One fear that many astronomers have of comets is that one might crash into the earth causing severe damage. In 1994, many astronomers witnessed the crash of Comet Shoemaker-Levy into Jupiter. This crash created huge, dark "holes" in Jupiter's atmosphere and "wreaked damage that was visible long afterward". If a comet is set on course to hit the earth, it is going to hit it. Many small comets and meteors have hit the earth before, though they did not have as great of an effect as a large one would. The fact of the matter is that comets cannot be stopped(6). Fortunately for us though, they can be seen through telescopes. As long as we exist so will comets. And as long as there are comets, people will be peering up into the night sky, trying to catch a glimpse of something they have never seen before.

WWW Sources

1) The Great Comet of 1997 ,

2) Comet C/1995 01 (Hale-Bopp) ,

3) European Astronomers Discover New Type of Comet Tail ,

4) Composition of Comet Hale-Bopp Opens Window to Solar System Formation ,

5) Comet Science ,

6) The House of Comets ,

7) Comet and Meteor News Zone ,

8) Visiting with an Old and Active Friend ,

9) Hale-Bopp may have a Satellite ,

10) The Discovery of Comet Hale-Bopp ,

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