The Outer Planets    • Grades: 1–2, 3–5  There is a very great
distance between the inner and outer planets. This region is
called the Asteroid Belt and large chunks of rock swarm around
and around in it.   They are much bigger than the inner planets.
They are made mostly of hydrogen and helium.  The hydrogen and
helium are in the form of gas in the planets'atmospheres. The
outer planets have a lot of atmosphere.  The outermost part of
these planets may be slushy. Below the surface, hydrogen and
helium are in a liquid form. At the center is a rocky core.
Each of these huge planets has its own system of moons.  Rings
around Saturn have been seen for many years. They are probably
made mostly of water, ice, and other icy particles. Recently,
rings have been discovered around two more giant planets Jupiter
and Uranus. Scientists expect to find rings around Neptune, too.
Jupiter, the first of the outer planets, is the largest of all
the planets. Jupiter is so far away from Earth that it was hard
to learn much