14 thoughts on “Achievement Locked

  1. I thought the shape of the orbit also determined whether it was a planet or dwarf-planet. I think Pluto’s orbit was not in the same plane as the orbit of the eight planets. I don’t remember number of moons, or even possession of moons, qualified as a quality of a planet. According to Wikipedia, Haumea, a dwarf-planet, has a couple of moons.

  2. It was solely based on size, from what I heard. It makes sense, too. There are much bigger astronomical objects that we don’t call planets, so it was either upgrade those or downgrade Pluto.

  3. I was under the impression that the main reason Pluto was downgraded was because a planet has to sweep up sufficient debris in its orbit, and because Pluto passes through the Kuiper belt, it clearly hasn’t done that.

  4. A planet is determined by where the axis of rotation between it and its moon is located. If the axis is located inside the planet, then it is indeed a planet. The axis of rotation between Pluto and Charon is located in space, which means the two bodies rotate around each other.

  5. A planet has nothing to do with its moon.

    A planet in our solar system must orbit the Sun (not some other body), have sufficient mass to achieve hydrostatic equilibrium (be roughly spherical), and have cleared the neighborhood around its orbit. By that, they mean that any debris in the objects orbit must be either accreted, pushed out of that orbit, or brought into an orbit around the object or around the Lagrangian points of the objects orbit and the Sun.

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