The world's astronomers, under the auspices of the International Astronomical Union (IAU), have concluded two years of work defining the difference between "planets" and the smaller "solar system bodies" such as comets and asteroids. If the definition is approved by the astronomers gathered 14-25 August 2006 at the IAU General Assembly in Prague, our Solar System will include 12 planets, with more to come: eight classical planets that dominate the system, three planets in a new and growing category of "plutons" - Pluto-like objects - and Ceres. Pluto remains a planet and is the prototype for the new category of "plutons."Now, the simplest - and I believe most rational decision - would have been to simply drop Pluto from the roster and call it a chunk of the Kuiper Belt. But noooo... scientists are so fussy. This little piece of rationalization is cute:
With the advent of powerful new telescopes on the ground and in space, planetary astronomy has gone though an exciting development over the past decade. For thousands of years very little was known about the planets other than they were objects that moved in the sky with respect to the background of fixed stars. In fact the word "planet" comes from the Greek word for "wanderer". But today hosts of newly discovered large objects in the outer regions of our Solar System present a challenge to our historically based definition of a "planet".
Member of the Planet Definition Committee, Richard Binzel says: "Our goal was to find a scientific basis for a new definition of planet and we chose gravity as the determining factor. Nature decides whether or not an object is a planet."Right. Nature has been unable to sleep, trying to decide whether planetary body 2003 UB313 is a full-fledged "planet" or not.
Of course, every time I get to thinking about the outer solar system - that is, stuff beyond the asteroid belt - I keep thinking how much more there is to explore just within our own solar system, never mind the rest of the near galactic neighbourhood. And then I get depressed because we should already be doing this stuff.