Re: "Pluto Now Called a Plutoid"

In message <jridnfxvzcbapuDVnZ2dnUVZ_uqdnZ2d@xxxxxxxxxxx>, K_h <KHolmes@xxxxxxxxx> writes

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In message <PYKdnToYLvdOlenVnZ2dnUVZ_rbinZ2d@xxxxxxxxxxx>, K_h
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No. I have already answered this in previous posts; at least a couple times now. "Nearly round" in not a colloquial way of describing hydrostatic equilibirum. A world in hydrostatic equilibrium can be nearly spherical or nearly spheroidal, the former for a non-rotating world and the latter for a rotating world. So worlds can have things like mountains on them and thus can be "nearly spherical" or "nearly spheroidal".

I did not do any name calling and neither should you.

I wasn't name calling I was given my considered opinion based on this discussion. Your comprehension of perfectly simple English is remarkably poor and you are engaging in stupid complaints about perfectly grammatical standard English.

I get the distinct impression that you are a grammatical prescriptivist. Your pattern of bizarre objections to perfectly normal established linguistic usage and inconsistent quibbling to justify a position based on personal preference is quite reminiscent of grammatical prescriptivism.


And your point is still utterly absurd and by not backing down on this
you are demonstrating that you are an idiot. The parenthetical comment
can be omitted without altering the meaning of the phrase. Absolutely
nobody is confused about whether Saturn is in Hydrostatic Equilibrium.
The Dwarf Planet definition has some problems in relationship to smaller
spheroid bodies this does not affect the definition of Planet as any
body big enough to be orbitally dominant is going to be in hydrostatic
equilibrium (largely round due to its own gravity).

No. The IAU's defintion refers to objects that are in hydrostatic
equilibrium and are nearly round (i.e. nearly spherical). Very oblate
objects, that are not nearly spherical, can also be in hydrostatic
equilibrium. The parenthetical comment cannot be omitted without altering
the meaning of the phrase. Again, this was already answered in previous
posts but check again: http://en.wikipedia.org/wiki/Round

You do not understand what a parenthetical comment is. The whole point of a parenthetical comment is that IT CAN BE OMITTED WITHOUT ALTERING THE MEANING OF THE SENTENCE. It is NOT a restrictive clause. It appears to be intended to explain to a laymen roughly what hydrostatic equilibrium means, as hydrostatic equilibrium is a piece of technical vocabulary that a non-specialist is unlikely to have encountered.

No, there is no excuse for waiting. The IAU's definition does not cover all
kinds of systems that are bound to be out there. Yet again, that was
already explained in my previous post.

There is a definition that covers all known cases. It is intended as a working definition and will be extended as more stuff is observed. We don't have any great need to classify objects we can't see and are unlikely to see for quite a while yet. Although we have provisionally decided that an object too small to fuse Deuterium formed in a star like manner is a Sup-Brown Dwarf not a planet, this would mean a Jupiter sized body which wasn't a planet.

I should note that it was only with the discovery of several other Kuiper belt bodies that there was any great drive to define the class of bodies to which Pluto belonged.



All known exoplanets of main sequence stars fall well above the
gap in Figure 1 and would be classified as planets by the
criterion of dynamical dominance.

A moot point since gas giants will be discovered first. Dynamic dominance is a vague and ambiguous term and should not be used to define a planet. Imagine a solar system in formation and a growing planet that has to periodically "clear out" its neighborhood due to constantly influxing material. Under the IAU's bad definition, it is alternately a planet at sometimes and not at others. So the IAU's definition is really quite bad.

The IAU definition currently applies only to one mature system, it easily be extended to other mature systems. The formation phase is
rather short but the definition cannot easily be applied to them. You
could explicitly include the phrase "in a mature system" in the definition and classify protoplanetary systems separately. Or you could include "has cleared, or is in the process of clearing, its


Yes, you rightly point out other flaws in the IAU's definition; it does not distinguish between mature and immature planetary systems. The example definitions I suggested avoid this problem totally since they can be applied at any time to any world.

At the moment it only apples to a single system, which happens to be
mature. It apples to no immature systems and we have, so far, not
detected any immature systems so the working definition for exponents
has not had to deal with any as yet.

Again, no excuse for waiting.


The discovery of the first exoplanets demonstrated that planetary formation didn't typically proceed the way we had thought they proceeded. Any scheme of nomenclature we had devised beforehand would have been utterly inadequate to classify what was actually out there. This has resulted in the definition of several new classes of planet, such as Hot Jupiters. Any definition introduced now would probably poorly reflect what actually exists.

If it caused the Kuiper wall it is a planet as it has cleared its neighbourhood creating the Kuiper cliff. You are talking about a somewhat smaller body which had not cleared its neighbourhood, that would not be a planet.

It should be called a planet. Pluto, for example, has polar caps, an atmosphere, seasons, three moons, and interesting geological activity at its surface.

Being interesting does not make it a planet. Comets also have
atmospheres sometimes very big atmospheres. Pluto looks to be a
gargantuan comet.

Again, the nomenclature should cover everything that is bound to be out
there. Pluto looks nothing like a "gargantuan comet".


Actually it does, it appears to have been formed from the same bit of the sun's circumstellar disk as the short period comets and seems to be made of the same stuff. Which, on compositional grounds, make it a giant comet. If it were on perturbed onto an orbit which took it into the inner solar system it would look like a comet forming a coma and tail as its ices vaporised. Several other outer solar system bodies have previously displayed comet like behaviour, Chiron has displayed a coma and is one of a number of bodies designated as both a comet and an asteroid.



Asteroids are already Minor Planets, a term which denotes an entirely
disjoint set from Planet. As the new term Dwarf Planet does.

This only underscores the need to get better definitions for things
like "Minor Planets" and "Asteroids". A minor planet is not a
planet? Silly. A great way to define asteroids is as objects small
enough so that hydrostatic equilibrium does not apply.

You may think it silly but it has been the case for more than a century and a half that Minor Planet is a term for objects too small to be Planets and which aren't comets. It is a synonym for Planetoid and Asteroid. This has not caused any confusion. They are listed and named in the Minor Planets Catalogue.

"A minor planet is not a planet" is a contradiction in terms. Yes, for the last century there has been some very bad terminology.

No it isn't, it is perfectly normal English. Minor Planets aren't
Planets, Beach Volleyball [1] isn't Volleyball [2], Koala Bears aren't
Bears. A modifier and a noun denoting an entirely separate class from
the unmodified noun is hardly unusual or remotely ungrammatical.

Yes, "Koala Bears" is an example of bad terminology because it is
taxonomically incorrect (as the link points out). A few bad examples like
these do not justify such bad behavior by the IAU.


I note that you chose only to comment on one case where the terminology has been changed to reflect a better understanding of the facts. In many other cases, Moles, Golden Moles and Marsupial Moles or Crabs, Hermit Crabs and Porcelain Crabs or Chimps and Pygmy Chimps or Hippopotamuses and Pygmy Hippopotamuses, the noun with the modifier is not a subset of the noun without the modifier. It is perfectly normal English.



What is wrong with developing the definitions based on observations? If you over specify prior to observation you may find that your definition is a poor match for what exists. This sort of thing has been a persistent problem in biology, many folk classifications bear little relation to the underlying nature of the species concerned, as they were compiled in ignorance of the underlying evolutionary relationships.

This is why the definitions should be such that they are observation independent and will not change with new discoveries. The more science learns about stars does not cause a change in the definition of what a star is and this should be the case with any resonable definition of a planet. That is the case with the examples I provided.

You then end up with definitions that do not match well with what exists and then you either re-define the terms to match usage or abandon the term and use a new term with a more appropriate meaning.




We know what a Star is, and have now based the definition on the
fundamental physical characteristics. It is however nothing like the
original definition. The oldest definition was "lights in the sky other
than the Sun", then "fixed lights in the Sky" then "big hot discrete
things" then we eventually worked out what made them glow and switched
to roughly "discrete bodies big enough to fuse hydrogen or which have in
the past fused hydrogen" it has since been revised to exclude black
holes so is now "discrete bodies big enough to fuse hydrogen or which
have in the past fused hydrogen which are not within an event horizon".
That is hardly supportive of your case, while the membership of the
class has been reasonably stable (of known bodies only the Moon and some
Planets have been excluded and the Sun added) the definition has changed
massively.

No, it is very supportive of my case. Many definitions in science have
changed numerous times. The IAU's definition is no exception; it too will
be changed because it is so bad and so much has yet to be learned about
other solar systems. BTW, the current definition of a star does not
explicitly make reference to event horizons.
http://www.answers.com/topic/star


The term star is used to include White Dwarfs and Neutron Stars, both discrete stellar remnants, Black Holes, even when they are stellar remnants, are not counted as stars.

Doesn't the fact the current definition of so many thing is the product of a long period of revision indicate that we shouldn't adopt an overly prescriptive approach to classifying things we have never seen?
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Relevant Pages

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