12 planets - and more to come
August 16th, 2006
The IAU, currently meeting in Prague, has now published the draft resolution that will decide whether Pluto is a planet or not. The definition goes: “A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet.”
It is a broadening of categories, since it will include asteroid Ceres (discovered in 1801) and some other bodies, giving us a solar system with at least 12 planets.
Then it goes on to distinguis the eight classical planets; for historical reasons, “one may choose to distinguish Ceres from the classical planets by referring to it as a ‘dwarf planet.’”
In this taxonomy, Pluto and other bodies that make the first definition but have a more anarchic behaviour - “highly inclined orbits with large eccentricities and orbital periods in excess of 200 years” - than the classical planets, are called Plutons.
And, let’s not forget, “minor planet”, used quite often in textbooks, names of institutions, publications &c, is gone.
The full text of the draft is here. (Borges’ classification of animals is here. Sorry, could not resist.)
Voting will take place on August 24. The world will be listening …
Michael E. Brown, whose team has discovered a number of Kuiper belt objects, gives the draft resolution good chances of passing:
Most people might think that a proposal to suddenly go from 9 to 53 planets would have no chance of passing, but I give this one good odds of passing the IAU vote. Why? It sounds scientific, it saves Pluto, and it suddenly makes many more people discovers of planets. Of course, it does even greater damage to the popular concept of the word planet by suddenly adding 44 new ones, all of which are so small that they could easily fit all together inside the earth’s moon (which, of course, doesn’t count as a planet) with plenty of room to spare, but perhaps that’s a small price to finally have a definition after all of this time.
Entry Filed under: astronomy
1 Comment Add your own
1. The Trading Zone: A Scien&hellip | August 19th, 2006 at 10:28 am
[…] Daniel Fischer, present at the IAU General Assembly in Prague, reports to the HASTRO-L mailing list that the first open debate, in which only planetary scientists took part, about the proposed resolution took place Friday afternoon. It lost about 60:40 against an alternative which would exclude Pluto. Seems also that “plutons” was rejected by a large majority. […]
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