The Planets and Space Exploration
The four rocky planets
at the center of the solar system
Mars, are known as the inner planets.
Neptune are all composed primarily of gas and are
known as the outer planets.
There are thousands of smaller, icy not-quite-planets in the space beyond Neptune. They include the dwarf planets Pluto, Haumea, Eris, and Makemake.
The asteroid belt, between Mars and Jupiter, is made of thousands
of chunks of rock which travel around the Sun. The largest asteroid, Ceres, is also a dwarf planet. Comets are small icy bodies that travel past the Sun and give off gas and dust each time they pass by.
have travelled to all the planets in the solar system (except Pluto) and
taken pictures of the planets and many of their moons. They have also
taken measurements that tell us what the planets are like inside.
Big, Bigger, Biggest
A Solar System Model Builders Guide
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