Pluto was officially stripped of it’s status as a “planet” today by the IAU after lengthy, contentious discussions that bordered on combatitive. In resolutions 5a, 5b, 6a, and 6b the august body of astronomers meeting in Prague defined clearly (for the first time since Gallileo) what the entrance requirements are to the elite status of planet (aka “classical planets”), the lesser status of “dwarf planet” (which Pluto is the prototype) and SSSB‘s.
So the last planet is now officially Neptune, and at this time there are three identified “dwarf planets”: Pluto, the large asteroid Ceres (once also identified as a planet) and Xena. Xena (aka UB313) is actually larger than Pluto. Xena and the status of Charon, the largest of Pluto’s moons, is what brought all of this to a head late last year and earlier this year. Many called for Xena to be a planet and some called for Pluto and Charon to become the solar systems first binary planet.
Now for the official definitions:
1) A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
(2) A dwarf planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.
(3) All other objects orbiting the Sun shall be referred to collectively as “Small Solar System Bodies”.
So Pluto is no longer a planet since, though it passes hurdles 1a and 1b, it has not cleared 1c since it has not cleared its own orbit (its orbit overlaps with Neptune’s). Pluto’s got the mass, but the movement just doesn’t cut it.
Similarly Charon, the almost Pluto sized moon of Pluto, which was being considered for elevation to planet-hood, is no longer eligible for any status except “moon” since it does not orbit the sun. Ceres and Xena will now also be known as a “dwarf planet” since neither of them have cleared their own orbit.
Or maybe they just stripped Pluto since they discovered it had been bulking up on PED‘s.
Its a good thing NASA launched the New Horizons mission back in January! Who knows if they could ever get approval to spend such a giant budget on a mission to a “dwarf planet”.
One Comment
Very interesting. I also hear that Dick Pound was quated that all planets are dirty and using PEDs. The only way a planet like Mercury can acheive its orbiting speed is through doping.
Another rumor surrounding Pluto being stripped is the Franch revenge for EuroDisney.
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