The Solar System - Comets

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  1. kkrish

    kkrish IL Hall of Fame

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    Comets

    Comet.jpg

    Picture courtesy : nasa.gov

    Comets are the most abundant type of body in the Solar system. Up until some years ago they were thought to be rare visitors from the outer solar system to the inner solar system, passing close to the Earth.

    Comets, the name meaning “long-haired” in Latin, are objects whose ices can vaporize in sunlight and form an atmosphere and sometimes a tail of dust and gas.

    Scientists believe that comets are the debris left from the solar nebula which condensed to form the Sun and planets in our solar system. Scientists think that about 100 million comets orbit the Sun.

    The parts of a comet

    A comet is made up of a center called the nucleus and a hazy cloud known as the coma. Scientists believe that this nucleus is made up of a mixture of ice, gases, dust, and rocky material, generally described as a dirty snowball.

    sciencecource.com.jpg
    Picture courtesy: sciencesource.com

    Sometimes the Sun’s gravity pulls a comet from its orbit towards it. When the comet comes closer to the Sun, the Sun’s heat causes the ice in the nuclei to evaporate. The dust and gases in the coma are released. The solar winds from the Sun blow the evaporating material out as a stream, forming the comet’s tail. The tails points outwards from the Sun and can reach 150 million kilometers long!

    Each time the comet passes close to the Sun, it loses some of its material. Over time, it will break up and disappear completely.

    Many comets enter an elliptical orbit and repeatedly return to the inner solar system where they can be viewed from Earth at specific times. A comet does not give off any light of its own. What seems to be light from the comet is actually a reflection of our Sun's light. Sunlight bounces off the comet's ice particles in the same way light is reflected by a mirror.

    A comet's tail can be millions of kilometers in length, but the amount of matter it contains can be held in a large book bag.

    Where do the comets come from?

    At first it was thought that comets originated from the Kuiper belt. However, studies have proven the objects in the Kuiper belt are stable. So comets must be originating from somewhere else.

    Astronomers now think that most of the comets originate from the unstable Scattered Disc, an area of objects that overlap the Kuiper belt and extend up 100 AUs beyond, above and below it.

    Comets are broadly categorized into types – long-period comets and short-period comets.

    Short period comets, of which Halley's Comet is the most famous, reappear within a 200 year time frame. Halley's makes an appearance once every 76 years. The comet was named after Sir Edmond Halley.

    Halley's comet
    Haley's comet Wikipedia.jpg
    Picture courtesy: Wikipedia

    Long period comets seem to originate from the Oort cloud.

    Raw Materials for Life?

    Comets and asteroids probably delivered some of the water and other ingredients that allowed the complex chemistry of life to begin on Earth. The amino acid glycine was discovered in the comet dust returned to Earth by the Stardust mission. Glycine is used by living organisms to make proteins. The discovery supports the theory that some of life's ingredients formed in space and were delivered to Earth long ago by meteorite and comet impacts.

    Protection from Potential Impacts

    While comet impacts could have been the reason for life originating on the Earth, any more impacts could end life as well.

    Scientists and astronomers are now discovering more and more asteroids and comets that have irregular orbits that may bring them close to Earth. While the possibility of hitting the Earth is rare, we need to know more about them in order to be better prepared.

    Information sources: Book -Asteroids, Meteorites, and Comets – Linda-T. Elkins-Tanton; NASA
     
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  2. kkrish

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