Why isn’t Pluto a planet any more?

Pluto no longer a planet

Pluto isn’t alone.

Pluto’s identity as a planet was called into question when discoveries were made in the far reaches of the solar system. Eris, Sedna, Makemake, and Haumea are just a few of over 1200 objects discovered beyond Neptune.

This forced astronomers to come up with an official definition of a planet. They argued until they came up with three requirements.

  1. It must be in orbit around the Sun.
  2. It must be big enough to be pulled into a sphere by its own gravity
  3. It must have cleared the neighbourhood around its orbit of other objects.

Put simply, Pluto didn’t meet the third criterion. This makes it a dwarf planet, along with Ceres, Haumea, Makemake, and Eris. Astronomers think there could be thousands of ‘dwarfs’ out there.

Short answer: Astronomers found so many ‘Plutos’ in recent years that they had to come up with an official classification system for planets and other objects.

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