I not only agree, I was planning on writing up a post this evening that made that same point. You beat me to it.

With Mars, the IAU decided that since we have additional data, we can make better and more illustrative placenames than were used for the low-resolution telescopically viewed features. Thus mares became plana and planitias, bright points became mons, etc. Some features retain their original names -- Hellas comes to mind.

I still think of Mars in terms of Syrtis Major, Mare Meridiani and Mare Cimmerium, though... and Nix Olympica. More a product of what I learned as a child than anything else, I'm sure.

-the other Doug

Not another comment on the basic debate, I'm done with that, but I thought this Comment submitted after an MSNBC "Cosmic Log" interview with Alan Stern was quite amusing...

"A "Scientist" is an entity that orbits a central idea & clears its area of all facts & figures. An entity that orbits a "scientist" is a "specialist". An entity that has not cleared its area of facts & figures is a "research student"."

However, calling this application of nomenclature "not a perfect fit" is like calling Mariner 1 "not a total success."

The great contribution of the IAU's effort to name these various classes of body is that one day it will be remembered as a failure in nomenclature the way that cold fusion is remembered as a failure in application of the scientific method.

"Never let scientists name your product."

The interesting thing is that star nomenclature has proceeded fairly smoothly. Supernova, white dwarf, neutron star, pulsar, black hole -- all of these terms were examples where the scientists basically got it right on the first try. But even before 2006's controversy, we had "plutinos", "KBOs", and "TNOs". Now we have "dwarf planet", "plutoid", and two controversial attempts at "planet". I think part of the answer is that people didn't previously have any concept of any of those star types until scientists theorized or discovered them. The terms described new things; they didn't replace terms.

But we've had fully six terms for denoting Pluto (not counting "Pluto" and "minor planet") with one of those terms given two new definitions. Any way you slice or dice it, you can tell when a good job is being done and when a poor job is being done, and seven categories for Pluto is not a good job being done. It's horrendous.

I noticed this in the IAU's press release
http://www.iau.org/public_press/news/release/iau0804/

I guess this means 2005 FY9 and 2003 EL61 will be treated as Plutoids at least for the purpose of naming.
How this affects the naming isn't apparent as there is no mention of a different naming convention being used for plutiods or dwarf planets in the press release or on the IAU's webpage.

In my opinion, IAU should only officially sanction notions and names crataed naturally for years and accepted by planetary science community, but should not create them ad hoc.

The two cases are not parallel. Nobody (so far) has attempted to re-define the word "star" by excluding neutron stars and white dwarfs from being regarded as stars. A white dwarf, for example, is (AFAIK) still regarded as a kind of star. That is, "white dwarf" is merely a subcategory of "star". (Even a black hole, for all its outwardly bizarre characteristics, is at its heart basically a star. A DEAD star. Just as neutron stars and white dwarfs are (nearly) dead stars. That is to say, they are the cinders/corpses of the objects they used to be--back when they were still alive and well and burning hydrogen.)

In contrast, the IAU definition specifically excluded "dwarf planets" from the category of "planet". As Betelgeuze pointed out earlier in this thread, that was "like saying a human dwarf is not a human". That is, such an exclusion would carry the implication that "planet" and "dwarf planet" were fundamentally different kinds of celestial objects, just as "star" and "planet" are (intermediate types like brown dwarfs notwithstanding) fundamentally different.

======
Stephen

Since this is another "argument from linguistics," I want to point out that it's kind of unreasonable. Note that a lightning bug is not a kind of lightning. There's probably some instance elsewhere in scientific nomenclature where a dwarf X isn't actually an X.

A black hole, by the way, is a very special thing, in that the dividing line really is so sharp that a difference of a single kilogram of mass (in theory) separates a black hole from a neutron star. As a paper in Science a year or two ago showed, there's even a fairly sharp line at the lower end of stars -- a minimum mass for fusion. I'll bet there's a bright line in planetary mass too -- above which you always get a gas giant -- so there might even be a range of "forbidden" planetary masses. That would be one heck of a bright line. We'll just have to get more data to be sure.

--Greg

"Since this is another "argument from linguistics," I want to point out that it's kind of unreasonable. Note that a lightning bug is not a kind of lightning. There's probably some instance elsewhere in scientific nomenclature where a dwarf X isn't actually an X."

But a lightning bug is a type of bug (though this term is not scientific but colloquial). The first word, lightning, is the adjective modifying the noun bug, meaning the object is a type of bug, the same way the word dwarf in "dwarf human" is the adjective modifying the noun, human, indicating a type of human.

Well, with a few years of professional experience in linguistics and a PhD minor in it, I'll chime in.

A noun phrase has a head noun, and it's usually the case that the thing referred to by the noun phrase is also an instance of the class of the head noun. And "lightning" is not the head of "lightning bug"... "bug" is. And a lightning bug IS a kind of bug. There are also cases of noncompositionality, where a lexical term with multiple word-tokens both of which happen to be words on their own are nonetheless totally unrelated semantically: The poker hand "full house" is not a house.

So while in principle a shadowy committee could create a term like "dwarf planet" and then claim that it is as unrelated to planets as Long Island iced tea is to actual tea, that would be disingenuous in this case, and I don't think anyone's claiming it.

Honestly, if you're hung up on making differentiations, then simply call everything big enough to round itself and that primarily orbits the Sun a planet. Then subdivide into:

Rocky Dwarf Planets: Mercury, Ceres
Icy Dwarf Planets: Pluto, Eris
Terrestrial Planets: Venus, Earth, Mars
Ice Giant Planets: Uranus, Neptune
Gas Giant Planets: Jupiter, Saturn

The only subdivision that is likely to see any change in the future will be Icy Dwarves, of course. And there *is* actually a good argument to be made to remove Pluto/Charon from its subdivision and create a new one, Double Planets, for any pair of objects big enough to self-round which orbit each other around a common point not contained within the surface of either planet. Fact is, we're probably likely to find many other such double planets out in the realm of accretion-without-perturbation (i.e., away from the gravitational harmonics Jupiter and Saturn created in the "main" system).

Heck, this could be exciting -- right now, our own team, the Terrestrial Planets, are in the lead with three! Those Icy Dwarves are on our tail, though, with two and more on the way! It looks like someone's making a move to pass around the outside!

(OK -- so I'm just thinking, if you could get the average NASCAR fan interested in the Solar System, it would have to be a good thing... *grin*...)

-the other Doug

Sigh. People are getting too serious again; it's probably time for someone to delete the thread.

My point was that in language the whole isn't always the sum of its parts. On reflection, trying to work in the Mark Twain quip about lightning/lightning bug was probably too cute. Here's one I'm sure you'll love. A "minor planet" isn't a planet. Anyone disagree? :-)

Summary: If you want to argue the term is bad, do it on a scientific basis. Don't appeal to linguistics.

--Greg

I hope you weren't intending to suggest that linguistics isn't a science. But of course, as a science, it deals with different questions than astronomy: it doesn't answer the question of how the natural world is categorized (if at all), but rather how human minds categorize their experiences using language. To some extent, both questions are being discussed here, which is itself a kind of category error; the two questions "is Pluto a different category of object from Mercury" and "does it make sense to call that category, if it exists, 'dwarf planet' or 'plutoid'" are just not the same kind of question.

As for "minor planets" vs. "planets" -- this is a bit of terminological sloppiness. From Copernicus on down to the turn of the 19th century, anything (other than comets) that orbited the Sun was a "planet" -- even moons were "planets" in some astronomical writings for a while. When asteroids popped up, they were "planets" too, to everybody but the far-sighted William Herschel. When the asteroids were finally downgraded, they remained, in a sense, "planets" -- just "minor" ones. The other eight objects should have been "major planets", but as they were the ones that had been called "planets" from a much earlier period, it was easier just to say "planet" instead of "major planet".

But if we wish terminological consistency, then "planet" should be the general name for any periodic object in solar orbit, and "planets" can then be subdivided into "major" and "minor" -- and now, apparently, "dwarf". But of course terminology is not consistent.

Easy on NASCAR fans