Thursday, June 12, 2008

Pluto is not a planet, it's a "Plutoid"

If Pluto is not a planet, what is it? What do you call a large body in an elliptical orbit around the Sun that still does not quality for the new International Astronomical Union (IAU) definition of a planet? The IAU has now, in essence, allowed Pluto to save face just a little bit by announcing "plutoid" as the new term for this class of objects IF said objects are beyond the orbit of Neptune.

COMMENT: The IAU's press release really does not make this very clear to the layperson. Some things are just supposed to be what they've always been called. As Stephen J. Gould argued, a brontosaurus should be a brontosaurus even if the rules of nomenclature call for "apatosaurus." And Pluto just should have been given a special exemption for new classifications and labeled a planet simply because the whole world has called it that ever since it was discovered.

From the IAU:

"Plutoids are celestial bodies in orbit around the Sun at a distance greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighbourhood around their orbit. The two known and named plutoids are Pluto and Eris. It is expected that more plutoids will be named as science progresses and new discoveries are made.

The dwarf planet Ceres is not a plutoid as it is located in the asteroid belt between Mars and Jupiter. Current scientific knowledge lends credence to the belief that Ceres is the only object of its kind. Therefore, a separate category of Ceres-like dwarf planets will not be proposed at this time."

No comments: