Astronomy

Almost two years after introducing the category of dwarf planets, the International Astronomical Union (IAU) General Assembly now decided on a name for transneptunian dwarf planets similar to Pluto. The name “plutoid” was proposed by the members of the IAU Committee on Small Body Nomenclature (CSBN), accepted by the Board of Division III, by the IAU Working Group for Planetary System Nomenclature (WGPSN) and approved by the IAU Executive Committee at its recent meeting in Oslo, Norway.

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.

In Oslo, members of the IAU also discussed the timing involved with the naming of new plutoids. Again, it was decided that, for naming purposes, any Solar System body having (a) a semimajor axis greater than that of Neptune, and (b) an absolute magnitude brighter than H = +1 magnitude will be considered to be a plutoid, and be named by the WGPSN and the CSBN. Name(s) proposed by the discovery team(s) will be given deference. If further investigations show that the object is not massive enough and does not qualify as a plutoid, it will keep its name but change category.

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