Experts meet to decide Pluto fate, Finally we'll know what a 'planet' is... Options

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One of many articles regarding the upcoming conference...

Experts meet to decide Pluto fate

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In the news ...

Pluto the Ninth, Xena (2003 UB313) the
Tenth, and brighter than Pluto after that

Tom Gehrels, University of Arizona, USA

The regular asteroid observers, including amateur astronomers, are doing well with their CCDs in faint follow-up astrometry. However, large wide-angle telescopes and special equipment are needed to explore the outer solar system, including the rare objects that might qualify as planets. The searching is done with expensive telescopes by experts who are not always asteroid observers. The greatest encouragement for exploration of the outer solar system is the excitement that a new Planet might be found. Observatory directors and funding agencies are well aware of that.

This proposal is therefore to stay with the 75 years of popularly considering Pluto the Ninth, as the IAU agreed to in Manchester, and to adopt Xena as the Tenth Planet because it is intrinsically brighter than Pluto. The proposal is further that the same accurate and convenient criterion be used for naming an Eleventh Planet and so forth, namely that they be intrinsically brighter than Pluto, measured in “absolute V-magnitude.” Pluto's absolute visual magnitude is –0.76, Xena's –1.2. The present proposal is written on behalf of people who are doing the observing and discovering, who see the need for prompt recognition and the fastest return in naming. This has been explained before, in Nature 436, 1088, 2005 and Sky & Tel. 111, No. 1, 14, 2006, and this Letter has been circulated in draft form, but there has been no response from the two naming committees of the IAU. Considering roundness due to gravitational stability is complex, time consuming, subject to change, and impossible due to faintness at great distance.

A compromise for proper study and distinction of the various objects and populations is to attach to Pluto and to any new Planets also the usual comet or asteroid designation. Xena already has 2003 UB313, which eventually will be a 6-digit catalog number. The dual assignment, as Planet and comet or asteroid, will also stimulate discussion in schools and colleges of the rich variety of solar-system objects.