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The giant gap between Mars and Jupiter marks the boundary between the
inner and outer solar systems. The inner solar system contains the 4 small
hard Earth-like planets. The outer solar system contains the 4 large gaseous
planets and Pluto. This gap is where most of the asteroids are located.
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Most scientist believe that Asteroids are fragments that were never
able to form a planet. They are made up of different materials, so it is
unlikely that they were once part of a planet that broke up.
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They are called "Minor Planets." There are several thousand of them,
some are as large as 1/3 of Pluto.
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There are three types of asteroids: Trojans (around Jupiter), Caustic
Group (move crazily among planets) and Near Earthers (close to Earth).
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The largest asteroid has been named Ceres. It is over 600 miles in diameter.
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Asteroids do not travel in set orbits like the planets. They are pulled
by the gravity of Jupiter and Mars.
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Sometimes Asteroids bump into each other. When they do, pieces of rock
break off. These pieces may streak through the sky toward Earth. They look
like bright fireballs and are called "Meteors."
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When a Meteor hits the Earth it makes a deep crater and then shatters
into smaller pieces. Once they have hit the Earth, they are called "Meteorites."
They can give scientists valuable clues to the origin of our solar system.
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Asteroids contain valuable minerals.
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One theory holds that an Asteroid hit Earth 65 million years ago and
might have caused the end of the dinosaurs, and the onset of the age of
mammals.
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Some scientists believe that about 4 billion years ago another asteroid
hit Earth in a terrific impact, causing it to spin rapidly. Debris launched
into space from the impact might have formed our moon.
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For the very first time man has landed a spacecraft on an asteroid,
named Eros on February 12, 2001. It landed at about 3:05 EST. The
spacecraft, called Near Earth Asteroid Rendezvous, or NEAR, showed that
the asteroid Eros is perhaps as old as the Earth. Eros is a Near Earther
type of Asteroid, and is about 196 million miles from our planet.
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