Comets (no, not asteroids, COMETS)
a)
Red = classroom comet Blue = real comet
When a real comet passes near the sun, the heat causes the ice in the comet to sublimate, thus releasing the grains of dust which were trapped in it. This dusty gas is heated by the sun; this cloud of gas then begins to glow and turn hot to form the comma, which, when in its perihelion period (when it’s closest to the sun) can become up to 10,000 km across. The comet’s dust and gas tails develop. When the comet passes around the sun around 500 times, the comet loses most of its ice and gas, leaving a rocky object which looks a lot like an asteroid.
c) A comet is made up of four parts: a nucleus, a coma, an ion tail, and a dust tail. The nucleus, which is the main body of the comet, is made up of a mixture of rocky particles of dust and ice. The ice consists of mainly frozen water, but also may include other substances that are frozen, such as: ammonia (NH3), methane (CH4), carbon dioxide/dry ice (CO2), and carbon monoxide (CO). It is believed by scientists that the nucleus of a comet is fragile.
The coma of a comet consists of gas and dust particles from ice vaporized by the sun. When the dust particles are pushed away from the coma by the sun’s radiation, a tail forms behind the comet called the dust tail. As this is happening, solar wind (which is the flow of electrically charged particles at high speed from the sun) changes some of the comet’s gases into charged particles (also known as ions). The ions stream behind the comet, thus forming an ion tail. Also, since the comet tails are pushed by solar radiation and solar wind, the tails always point away from the sun.
d) Most comets come from the Kupier belt, which is beyond the orbit of Neptune; however, comets can be found all over the solar system. A comet’s orbit is elliptical, with the sun near one end. The period when the comet is closest to the sun is called the the comet’s perihelion, and the period when the comet is farthest from the sun is called its aphelion. There are two types of comets: short-period comets, which take less than 200 years to complete their elliptical orbits, and long-period comets, which take 200 or more years to complete their orbits (note: for the answer to the “What happens to a comet’s orbit as it changes mass around the sun?” question for part d), please refer to the second paragraph of part c).
e) Comets are important as they may have brought life to Earth. Some scientists speculate that comets that crashed into Earth during its early stages brought water and a whole variety of organic materials (such as carbon) to earth.
f) Some of the things NASA is currently doing to study comets is: 1. simulating comet collision with wandering objects in space, and is analyzing its results from its Big Impact mission, which was launched and smashed into comet Tempel 1 on July 4th, 2005 (some 4th of July fireworks THAT must have made 
) to find out what is on the interior of a comet’s nucleus.
In the future, NASA hopes to get the results of its Stardust mission. The Stardust mission was launched to bring back sample particles form Comet Wild 2 as well as from interstellar dust. A great deal about the compositions of the early solar systems building blocks is expected to be learned from these particles, as well as what our neighboring stars are made of.
Sources:
Real comet info from: Yeomans, Donald K. “Comet.” World Book Online Reference Center. 2005. World Book, Inc. http://www.worldbookonline.com/wb/Article?id=ar125580.
http://nineplanets.org/comets.html
http://science.nationalgeographic.com/science/space/solar-system/asteroids-comets-article.html
http://cse.ssl.berkeley.edu/SEGwayEd/lessons/cometstale/frame_orbits.html
http://www.nasa.gov/mission_pages/deepimpact/media/f_whycomets.html
http://www.nasa.gov/centers/ames/multimedia/images/2005/comets.html
http://www.nasa.gov/mission_pages/deepimpact/main/index.html
http://www.nasa.gov/mission_pages/deepimpact/media/spitzer-di-090705.html
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