Xena Awarded "Dwarf Planet" Status, IAU Rules; Solar System Now Has Eight "Classical" Planets Honey, I Shrunk the Solar System What's in a Name? Explore ALL Worlds, says The Planetary Society -- Planet or Not -- Pluto is Waiting for Us JHU: Astronomers Mixed Reactions to Pluto's "Demotion" IAU 2006 General Assembly: Result of the IAU Resolution votes
Editor's note: While it is important to have some precision when it comes to scientific terminology, there was a certain silliness to this whole process. It is almost as if the words were more important than the objects they described. Oh well.
I can't wait for the IAU to re-look at the definition of the term "planet" when it comes to other solar systems. How will they handle the large bodies that orbit brown dwarfs? What about planet-sized bodies (already observed) that don't orbit a star? What about planets stuck orbiting inside an expanding red giant giant? What about bodies that orbit multiple stars? What about planet-sized objects which have formed in a young solar system - but are still sweeping up debris in the neighborhood?
Reader note: Hi Keith: Several of the objects you describe have already been defined by the IAU's Working Group on Extrasolar Planets, which I chair. Please see: http://www.dtm.ciw.edu/boss/iauindex.html Our working definition of a planet was approved at the last IAU General Assembly, in Sydney in 2003. - Alan Boss
Reader note: Dear Keith: It might be useful to remind everyone that while scientific societies are democracies (ideally, at least), science itself hews solely to the authority of Nature. - Sincerely, Bill McKinnon, Member of both the IAU (though not in Prague) and the DPS Committee
Editor's note: It is interesting to see how astronomers considering a much more expansive collection of objects (more than a hundred) viewed the definition of what a "planet" is as opposed to the group who confined themselves to the more parochial task of describing the worlds in our single, local solar system - one where local politics must be taken into account!
I got to thinking. If Pluto, Ceres, etc. are "dwarf planets" - this is in comparison to what? Earth? Jupiter? I haven't done the math but I would think that a comparison between Ceres and Earth would not be all that different in terms of relative size between Earth and Jupiter - both of which are "planets". Why is this size disparity OK in one direction - but not another? Looking at the extrasolar planets discovered thus far (albeit the largest are the easiest ones to find) many are much larger than Jupiter. Wouldn't that make Earth a "dwarf planet" too when compared to the range of objects that we call "planets" thus far?
We already routinely refer to "terrestrial" planets and "gas giants".... no one has every really baselined those terms - yet I do not see IAU types getting upset when the terms are used.
And yet this definition of "planet" vs that of "moon" is also silly when you somehow denigrate large worlds like Titan, Triton, and Ganymede etc. as being just "moons" when they are larger than a classical "planet" (Mercury) while other "moons" can be a rock just a few kilometers across. Its is time for the keepers of terminology to describe reality as it actually is - not as they would like it to be so as to make grant proposal writing easier.