• Question: Why is Pluto not a planet any more?

    Asked by joDuck to Hephzi, Imogen, Jen, Jennifer, Tom on 9 Mar 2015.
    • Photo: Jennifer Rudd

      Jennifer Rudd answered on 9 Mar 2015:

      I think they decided it was too small to be called a planet. It makes me sad that Pluto was downgraded.

    • Photo: Thomas Barrett

      Thomas Barrett answered on 9 Mar 2015:

      The definition of planet set in Prague in 2006 by the International Astronomical Union (IAU) states that, in the Solar System, a planet is a celestial body which:
      1) is in orbit around the Sun,
      2) has sufficient mass to assume hydrostatic equilibrium (a nearly round shape),
      3) has “cleared the neighbourhood” around its orbit.

      Pluto fails mainly on the 3rd criteria. It has been downgraded to a Dwarf Planet. The International Astronomical Union (IAU) currently recognizes five dwarf planets: Ceres, Pluto, Haumea, Makemake, and Eris.

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