Comets was once described by Fred Whipple as nothing more than a dirty snowball that travels through space. Because of comet size and the great distances they travel, it is not easy to work out their journey path, some comets such as Halley, the path is known, it travels out past Uranus before returning to the Sun. Apart from their composition, ice and dust, they also have tails which asteroids don`t. They have been seen throughout history and probably the most famous appearance of a comet that has been recorded is Halley Comet which appeared at the time of the Battle of Hastings (1066). Halley`s Comet appears on the Bayeaux Tapestry which chronicles the battle. The make-up of a comet is theorised as being dust and blocks of ice held together by the cold. A theory has been put forward that life on Earth hitch-hiked on the back of a comet due to its make-up. This has been neither proved nor disproved as far as I know. Recently due to the outbreak of the SARS virus, scientists are thinking about whether the so-called Emerging Diseases have come from Comets as they pass-by. It is an interesting theory which could be worth looking into. Comets take a highly elliptical path whereas planets are more circular. The picture below is of a comet showing off its tail as it gets close to the Sun.
Some people think that long distance comets such as Hyakutake could originate from the Oort Cloud , a hypothesized area that is located about 1 light year away from the Earth.
In March 2004, the European Space Agency (E.S.A.) launched the Rosetta space probe on a ten year mission to rendezvous with P67/Churyumov-Gerasimenko and land a space probe called Philae on the surface. On the 10th December, it was announced that results back from the successful landing of the probe and the experiments that it had carried out, water on Earth had not originated from comets. However it is only one comet that they`ve been looking at and more research is needed. Some scientists are now turning their attention to asteroids which they believe could contain water.1
The main difference is what makes up the two objects, comets are made up of dust and ice whereas asteroids are rocks and metals. Comets when they get close to the Sun will burn away and produce a tail. Comets can have very long journeys round our Sun, sometimes never to be seen again in our lifetime whereas asteroids are in the asteroid or kuiper belts.
|C / 1964 N1 Ikeya||391||1964-8-1|
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