Original URL: http://www.theregister.co.uk/2008/06/12/plutoids/
Pluto awarded celestial consolation prize
Dwarf planets to be known as 'Plutoids'
Posted in Space, 12th June 2008 09:52 GMT
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The International Astronomical Union (IAU) has awarded poor old Pluto a consolation prize following its controversial demotion from the league of planets - other similar dwarf planets will henceforth be called "plutoids".
Pluto was given its marching orders [1] back in 2006 in an IAU resolution [2] which clarified:
(1) A "planet" [1] 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 [2], (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.
Pluto, the IAU concluded, was a "dwarf planet by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects".
Well, these trans-Neptunians are now called Plutoids, the IAU executive committee has announced. According to Reuters, the group currently comprises just Pluto and Eris, which is actually bigger [3] than the former planet, although astronomers "expect to find more".
The biggest known asteroid Ceres [4], meanwhile, doesn't qualify for membership of the Plutoid club since lies in the asteroid belt between Mars and Jupiter. ®