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Killer Asteroids
-is one lurking in our neighborhood?
By Tim Hunter
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"…although the annual probability of the Earth being struck
by a large asteroid or comet is extremely small, the
consequences of such a collision are so catastrophic that it is
prudent to assess the nature of the threat and prepare to deal
with it"
David Morrison
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Introduction – Asteroids, Meteoroids, and Impacts on the
Earth
Asteroids are small rocky or metallic bodies orbiting the Sun.
They are considerably smaller than the traditional planets and
are often called "minor planets." The largest asteroid is Ceres
with a diameter of 1000 km. While sixteen asteroids have
diameters of 240 km or larger, the vast majority are a kilometer
in size or less (Hamilton).
Thousands of asteroids are known and thousands of small
asteroids are being discovered every year. Most of them lie in
the Main Belt between the orbits of Mars and Jupiter, but some
of them are in stable resonant orbits associated with Mars,
Jupiter, Saturn, Uranus, and Neptune. Their origin is unknown,
but the current thinking favors their being left over material
from the formation of the Solar System that never coalesced into
a larger body (Moore, 2002).
The Earth is constantly bombarded with debris (meteoroids) from
space. This debris represents bits of rock and metal left over
from the formation of the Solar System as well as varying-sized
chunks of asteroid fragments produced and scattered in our
direction by countless asteroid collisions mostly in the Main
Belt. As comets swing by the Sun, they leave debris in their
wake – tiny rocks and ices – which the Earth frequently
encounters. The amount of material being swept up by the Earth
is estimated at approximately 50,000 metric tons a year (MadSci
Network). This is a lot of material, though its contribution to
the overall volume and mass of the Earth is trivial compared to
the large size of the Earth. |
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