Orbital dominance!

The planet debate continues at the IAU 26th (or XXVIth for you Romans) General Assembly.  Interesting update today about the status of the draft proposal for a definition of a planet, released last week but subject to discussion and vote before becoming official.  In short, all your effort to create new 12-word mnemonics for remembering the planets has probably been for naught.

The main problem with the draft was that the definition was just too inclusive.  The liberally small size requirement could have potentially let several asteroids and Kuiper Belt Objects (KBOs) into the intentionally exclusive club of planethood.  Instead, the concept of orbital dominance has emerged from the conference as a better way to distinguish planets from everything else in the solar system.  If an object is the only major body in its orbit, that should count for something.  This concept lends weight to the nature of first eight planets, recognizing them as unique objects.  However, it eliminates Pluto.  Given that Charon is significantly close to Pluto in mass, neither is considered dominant.  It also pretty much slams the door on finding any other planets, a possibility the draft definition made very likely. 

So, Pluto, Charon, 2003 UB313, and other distanct KBOs will probably be banished to dwarf planet status.  Astronomers are still discussing possible names for these objects to separate them from asteroids.  The term "plutons" has already been dismissed.  "Pluton" is actually already a common geological term for igneous rocks (solidified magma).  I like this take on it, from the AP article:

"What were they thinking? The reaction in the geologic community was rolling of eyes," said Allen F. Glazner, a geologist at the University of North Carolina. "It would be like botanists trying to distinguish between trees and shrubs and coming up with the term 'animal.'"

I liked the 12 planet idea, but I think I'm happier with this definition.  The draft doesn't differentiate "major" planets, KBOs, and asteroids, just lumps them all together in one big happy planet family.  But I like orbital dominance, and using the word planet to mean something significant.  I'm guessing large, spherical objects in the Kuiper belt (i.e., Pluto and Friends) will end up being called Tombaugh Objects as a political way of recognizing Clyde Tombaugh's discovery of Pluto.  Seems nice, given that they're stealing a whole planet from him.

You also have to feel for the astrology community, who must have been primed for the 12-planet system.  It would have given them ready-made excuses for thousands of years of mistakes.  ("No, see if we'd have known about Ceres, we could have predicted you'd miss out on that big promotion!")

Posted at 05:04PM Aug 23, 2006 by WILSON, JOSHUA in Bits of news  |  Comments[1]