The not-quite-planets of the Solar System

September 1, 2021

You probably know about the Solar System's eight planets—but do you know our dwarf planets?

The dwarf planet classification was created in 2006, when the International Astronomical Union (IAU) stripped Pluto of its planethood.

The main difference between the two (beyond size) is whether the object has cleared its orbit of other debris; in Pluto's case, that's a no.

So far, the Solar System has five official dwarf planets, four of which lie in the Kuiper Belt beyond Neptune:

  • Pluto, the beautiful far-flung body that once reigned as the system's ninth planet (RIP 1930 - 2006).
  • Haumea, a ~620km-wide object which spins so fast it's squished like a football.
  • Eris, which is larger than Pluto and in part prompted the planetary demotion.
  • Makemake, a red-brown body with frozen methane and ethane.

Finally, there's Ceres, which lies much closer to home in the Asteroid Belt between Mars and Jupiter. It's definitely not an asteroid though; the dwarf planet comprises a full quarter of the belt's mass.

Sources and futher reading:

What is a dwarf planet? at NASA

Pluto and the developing landscape of the Solar Sysyem at IAU

Pluto, Haumea, Eris, Makemake, and Ceres at NASA.

Featured Image:

False Colour image of Ceres, captured by Dawn spacecraft. Credit: NASA/JPL-CalTech/UCLA/MPS/DLR/IDA

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