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  Asteroids
  An asteroid is a rocky mass up to several
hundred kilometers wide that revolves around the
Sun. Asteroids are sometimes called minor planets.
Most asteroids orbit in the
asteroid belt, a region
between Mars and Jupiter. Asteroids have uneven
shapes. Some have smaller asteroids orbiting
them. The smallest asteroids are pebble-sized. Most
asteroids complete a revolution in three to six years.
  Can Earth be hit by asteroids? It has happened,
and you can see the huge craters that have been
the result. Such collisions are very rare. Fortunately,
Jupiter’s gravity holds most asteroids in the area
beyond Mars.
  Most asteroids have odd
shapes. This one looks
like a light brown flying nose! The largest asteroids are nearly spherical in shape, with diameters of 250 to 1000 kilometers.
  Asteroid Gaspra
Gaspra was one of the first
asteroids to be studied up close.
It is only 19 kilometers long and
about 12 kilometers wide.
  Asteroid Ida
Ida is in the main
asteroid belt between
Mars and Jupiter. Ida is
about 58 kilometers
long and 23 kilometers wide.
Asteroid Eros In 2001, Eros became the first asteroid to
be orbited and landed upon
by a spacecraft. Eros is 33 kilometers long and
13 kilometers thick. This
image shows evidence of
craters, boulders, and layers
of rock.