Planet Nine is a hypothetical planet in the outer region of the Solar System. Their gravitational effects could explain the peculiar clustering of orbits of a group of extreme Trans-Neptunian Objects (ETNOs). If it does exist, Planet Nine is estimated to be an ice giant (similar to Neptune or Uranus) and is 10 times more massive than Earth. It is estimated to have an orbital period of 10,000 to 20,000 Earth years.
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