Plutoids: a new class of objects beyond Neptune, Astronomy, politics or damage control Options

[J.J.]

Can't add much other than to say that I totally agree with Nprev et al: definitions--and the languages they're couched in--are subjective fluid, while science is necessarily rigid and objective; it cannot be nominalist. Though I suspect time will gloss over most of the rancor associated with this conflict with respect to planethood, I don't think we'll ever have an answer that pleases everyone.

[Betelgeuze]

I like the term 'dwarf planet', what I don’t like about it is the fact that dwarf 'planets'(!) are not planets. That doesn’t make a lot of sense to me, its like saying a human dwarf is not a human.
Call Pluto, Eris and Ceres dwarf planets, but classify dwarf planets as planets just like you have terrestrial planets and gas planets.

Let the children only learn about terrestrial planets and gas planets and tell them there are dwarf planets too. Problem solved!

I wasn’t sure what to vote on, for me Pluto is a planet of the subclass dwarf planet, just like its both correct to say that Jupiter is a planet and a gas planet.

[Greg Hullender]

Nearly all English words are a bit fuzzy -- even scientific ones. Take "star" for example. Is a brown dwarf a star? If we agree stars have to fuse, then is a white dwarf no longer a star? How about a quasar -- is that a star? And is there a star so small that if we removed a few kilograms it would cease to be a star? Also, important distinctions like type G vs. type K are almost completely arbitrary.

Note that even the definition that says a planet is any non-fusing body that's large enough to be in hydrostatic equilibrium does have this fuzzy edge problem -- on the high and low ends both.

The fact that words have fuzzy meanings doesn't mean they're useless, but it does mean you need to think carefully about what you want to get out of a definition. Also, and most germane to the "what's a planet" questions, do you have enough examples to make a useful definition?

If we cast the problem as "how should we classify subtypes of non-fusing bodies in hydrostatic equilibrium," then I'd claim that since we only know of a couple dozen such bodies, it's not at all clear that we have enough data to make a proper definition. When we know of hundreds such bodies, we'll have a much better chance at knowing what's important and what's not. Until then, we're just guessing, and debate without data is almost always sterile.

--Greg

[tanjent]

I don't understand why this topic provokes so much emotion.

The more different space objects we identify and interact with,
the more details we will want to take into account when we try to categorize them.
And for the above mentioned continuum reasons, none of the categorizations will ever be a perfect fit.
But this shouldn't matter to the people here on this site who are already well aware of the
imperfections of whatever classification system is in force. When those imperfections become too
constraining, the system will be modified again, but it is only ever going to be an heuristic convenience.

It seems we are all up in arms about how OTHER people will be confused - children, politicians,
the man and woman on the street. How will the imperfections of the labeling scheme warp their
understanding of the underlying science? The incentive to learn more probably comes from the
subject matter itself. Some of those other people will push on to learn more and others won't. This
seems quite normal and not especially deplorable, since many of those who continue to rely on an
oversimplified and somewhat inaccurate view of outer space will obtain a deeper understanding of some
other area in which they become the experts who are best in touch with the underlying reality. I don't
worry that interested children are going to be stopped in their tracks by Pluto's demotion.

Disclaiming any serious knowledge of linguistics, I am still not too surprised that languages evolve.
All the heated debate is entertaining and certainly not harmful, and the fact that some organized group of experts is
trying to direct the process probably inspires a "Who do they think they are?" response, but ultimately the
constructs that survive will be those we find convenient to use. And after a while they won't seem so convenient
any more and something else will come along. "Plutoid" will do for now, but certainly not forever.

[Greg Hullender]

Note that there was a small fuss when they renamed the surface features on Mars, too. Who else remembers when Olympus Mons was called "Nix Olympica?" Scientists can handle change, when it's merited.

Had the IAU simply ruled that no KBO could be a planet, and that on those grounds, neither Eris nor Pluto was a planet, I think there would have been less fuss. Further definitions should probably have waited until we had more data on the Kuiper Belt and the regions beyond it (not to mention more data on extra-solar planets).

--Greg

[dvandorn]

Note that there was a small fuss when they renamed the surface features on Mars, too. Who else remembers when Olympus Mons was called "Nix Olympica?" Scientists can handle change, when it's merited.

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

[Stu]

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"."

[JRehling]

I don't understand why this topic provokes so much emotion.

The more different space objects we identify and interact with,
the more details we will want to take into account when we try to categorize them.
And for the above mentioned continuum reasons, none of the categorizations will ever be a perfect fit.

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.

[alan]

I noticed this in the IAU's press release

for naming purposes, any Solar System body having (a) a semimajor axis greater than that of Neptune, and ( an absolute magnitude brighter than H = +1 (see Notes) magnitude will, for the purpose of naming, be considered to be a plutoid, and be named by the WGPSN and the CSBN.

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.

[peter59]

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.

[Stephen]

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.

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

[Greg Hullender]

. . . that was "like saying a human dwarf is not a human

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

[laurele]

"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.

[JRehling]

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.

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.

[dvandorn]

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