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Solar System Distance Model
The planets nearest the Sun are very different from the
planets farther out in composition and structure.
Mercury, Venus, Earth and Mars are called the “inner” planets
because they occupy the inner part of the solar system. They are
also called the “terrestrial” planets, which means “earthlike”.
They are all small and rocky with iron cores.
Between the “inner” and “outer” planets is the asteroid belt.
Within the asteroid belt is Ceres, the largest asteroid, now
classified as a “dwarf” planet. Ceres is about 1/3rd the size
of the Moon.
Jupiter, Saturn, Uranus and Neptune are the “outer” planets
because they are in the outer part of the solar system. Jupiter
and Saturn are sometimes called the “gas giants” and Uranus
and Neptune are sometimes called the “ice giants”.
Past the outer planets is the Kuiper Belt. The Kuiper belt is
composed of millions of icy bodies. At least 5 have been
recently discovered that are about half the size of the Moon.
Pluto is a “dwarf” planet and Kuiper Belt Object.
Beyond the Kuiper Belt is the “Scattered Disk”, made of Kuiper
Belt Objects that have been flung out by gravity or collisions
into more elliptical and larger orbits. Eris, which is bigger than
Pluto, is a “dwarf” planet and a “Scattered Disk Object”.