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There are nine planets in our solar system. They range in size from the tiny Pluto, which
is smaller than the Earth's moon to the monstrous Jupiter, which some consider to be a
failed star. The closest planet to the sun is Mercury, the farthest is Pluto, most of the time.
For a period, Pluto ventures inside of the orbit of Neptune, making Neptune the farthest planet
from the sun for about 20 years. This last occurred from 1979 to 1999.
There is some debate about what a planet actually is. Some feel that Pluto is not large enough to be a
planet and is a member of the Kuiper Belt, which is a region of icy objects from about 30 AU to
1,000 AU from the sun. On the other hand, there needs to be a limit on when a large planet
stops being a planet and becomes a Brown Dwarf, which is a star that never gained enough mass to
start fusion.
Nonetheless, for the time being we have nine planets in our solar system, each having very interesting
features.
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