International Astronomical Union - The XXVIth General Assembly and The Definition of A Planet

The XXVIth General Assembly and The Definition of A Planet

The XXVIth General Assembly of the International Astronomical Union was held from 14 to 25 August 2006 in Prague, Czech Republic. On 15 August the Assembly decided to restore to individual members the right to vote on scientific matters, which had been removed from them at the XXVth Assembly in 2003. Among the business before the Assembly was a proposal to adopt a formal definition of planet. During the General Assembly the text of the definition evolved from the initial proposal that would have created 12 known planets in the solar system (adding initially the asteroid, for a short time around 1801 a planet, Ceres, Pluto's present moon Charon, Eris and would retain Pluto as a planet) to the final definition of a planet resolution that was passed on 24 August by the Assembly, which classified Ceres, Eris and Pluto as dwarf planets, and reduced the number of planets in the solar system to 8. The voting procedure followed IAU's Statutes and Working Rules. The General Assembly lasted 12 days and had 2412 participants, most of them for only part of the duration of the Assembly. 424 of the 9785 individual IAU members attended the Closing Ceremony on 24 August 2006. Following the Closing Ceremony, parts of the scientific community did not agree with this ruling, especially the specific wording of the resolution, and criticized IAU's authority to name celestial bodies. In the ensuing public debate, a number of laypersons expressed (at times strong) disagreement with the vote. Another, less vocal, fraction of the scientific community backs the resolution, including the discoverer of the dwarf planet Eris, Mike Brown.

A final decision was made, announced 11 June 2008, for acceptance of the term Plutoid and its official IAU definition:

Plutoids are celestial bodies in orbit around the Sun at a semimajor axis 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. Satellites of plutoids are not plutoids themselves.

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