As first reported by Bad Astronomer Phil Plait, the IAU will (a week from today) vote on a new definition of planet which will denominate 12 planets in our Solar System instead of 9, with many more – perhaps millions – waiting to be discovered!
Lia and Alan discuss the proposals before the IAU on the swings. Checking the mail, they happily report that it looks like Pluto and Charon will be designated as the first twin planets!Â
Why Pluto-Charon when our own Moon is larger than both Pluto and Charon? Because the barycenter of the Pluto-Charon system is outside Pluto, while, for the Earth-Moon system it is 1700 km below the surface of the Earth. Phil points out that, with the Moon receding from Earth at 4 cm per year, in about 40 million years [correction: make that about 3 billion years] the Earth-Moon barycenter will be outside the Earth and the Moon will then be designated a planet (that is, if the IAU doesn’t redefine planet before then).Â
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Below are the 3 new planets, and some planet candidates.
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Later Lia and Alan prepare for travel to Prague for the conclusion of this planet-shattering IAU meeting.