COMETS

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COMETS
By Matthew H and Callum F
St. John The Baptist
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From the ground, comets look quite small, white
streaks of light hanging motionless and calmly in
the night sky. In reality they're bulky objects
hurtling through space at unimaginably fast
speeds. Many years ago people used to think that
comets were huge balls of fire. However now we
know that they are solid, frozen, lifeless cosmic
icebergs. Furthermore, they would be dark and
invisible, if it were not for the heat of the Sun
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  Scientists believe that most comets in the
Solar System come from the Oort cloud - a ring of
around 10 million million icy objects which
resides around our Solar System, far beyond
Pluto's orbit halfway between the Sun and another
star (about 100,000 Au or 2 light years away).
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    A comet can easily be dislodged however (for
example under the influence of a passing star),
and may then come hurtling into the Solar System
when. Attracted by the Sun's gravity, it would
accelerate towards the Sun, building up speed and
eventually travelling extremely fast when it
reaches the planets. The potential for damage
upon impact with a planet is therefore very real,
as was shown when comet Shoemaker-Levy 9 crashed
into the surface of Jupiter in July 1994. Most of
the time they just zip around the Sun and then
back into outer space, but occasionally they get
trapped by Jupiter's gravity and make repeated
visits to the Solar System (eg Halley's comet -
see below) until they finally evaporate.
Picture from http//antwrp.gsfc.nasa.gov/apod/ap99
0814.html
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Comet Shoemaker-Levy 9, pictured here in a
Hubble Space telescope image, was broken into
many pieces during a close encounter with the
planet Jupiter in 1992. Two years later it came
so close to the planet that the fragments
actually plunged into Jupiter's atmosphere.
Picture from http//antwrp.gsfc.nasa.gov/apod/ap96
0502.html
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The dust tail shines by means of reflected
sunlight and is the part of a comet that is
usually easiest to see. A longer, with ions to
make uncharged molecules. blue-colour ion tail is
made of charged gas that glows as electrons
re-combine
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THANK YOU FOR WATCHING