IAU- Gatekeepers of the Dwarf Planet Classification?

[orcusthedwarf]

Full Disclaimer: I know the general consensus in the Astronomy community is what an object is labeled is not as important, as what its intrinsic properties are?
Where and how it was formed, etc? However, like so many others I do not feel that the IAU should be the official gatekeepers of the Dwarf Planet listings.
All the way in 2006 back when Pluto had its classification changed, the IAU stated there was a watchlist for about 12 potential dwarf planets to be included.
Flash forward 15 years later, and its all crickets. Despite having sufficient additional data to include: Quaoar, Gonggong, Sedna, and Orcus they remain incorrectly classified.
All but Gonggong were submitted for inclusion by Dr. Tancredi over a decade ago. NASA has even recognized Gonggong as a Dwarf Planet in an article.
The absolute magnitude requirement of greater than +1 just applies to the object being named.
Mike Brown, Dr. Tancredi, and Dr. Grundy all agree on Quaoar, Sedna, and Orcus.

To quote Mike Brown: "Free the Dwarf Planets!" I do not think there is any scientific reason for their exclusion at this point, its simply the IAU never intended to be the gatekeepers of this process.
They simply locked the door and threw away the keys. Only classifying 5 objects as Dwarf Planets is a total farce, and could not be further from the truth.

[PetersCreek]

Welcome to the CosmoQuest forums, orcusthedwarf. I've moved your thread to the Astronomy forum.

[Hornblower]

In my opinion there was ample justification for reclassifying Pluto into a separate subcategory with respect to the 8 undisputed major planets. The IAU simply did a dubious thing by considering about 400 out of the original 3000 or so delegates to be a quorum for this action, and then further hurt their credibility by saying such nonsense as "a dwarf planet is not a planet." Their wording of the gravitational criterion, an oversimplified "clearing its neighborhood", leaves a lot to be desired.

[grant hutchison]

... further hurt their credibility by saying such nonsense as "a dwarf planet is not a planet."

I've never understood why this phrase is so often reviled as "nonsense" (and worse), when there are many examples in English in which [adjective+noun] is not a [noun].
For instance, the prairie dog is not a dog, and no-one ever imagined for a moment that it was a dog. Lewis and Clark had actually spent a day chasing the things and had one in a cage in front of them when they bestowed the name, so it wasn't as if they had any doubts. They chose the name (influenced by the French name, petit chien) because prairie dog alarm calls sound like the bark of a small dog.
So a "prairie dog" is not a dog--it's a thing that lives on the prairie which shares some characteristics with a dog.
Dwarf planet--small object that shares some characteristics with a planet.

I'm not trying to defend the IAU's behaviour on this one, which was at best eccentric. Just wondering why people get riled up about the idea that a dwarf planet is not a planet.

Grant Hutchison

[Noclevername]

A planet that's small (dwarfish). Seems perfectly clear to me. Too bad the IAU can't see it.

IMO Pluto needs its own designation to acknowledge its historical value, like "honorary planet" or something.

[grant hutchison]

A planet that's small (dwarfish). Seems perfectly clear to me. Too bad the IAU can't see it.

Yeah, we should all be able to interpret newly coined technical terms however we like, irrespective of the definitions given by the people who coined them. That's definitely the way ahead.

Grant Hutchison

[Roger E. Moore]

I am not going to vote here (don't know enough about the contestants in the contest to make an informed decision), but I will say I always had difficulty with the "clearing the neighborhood" thing. I ran afoul of it in a long-ago thread here and am not eager to repeat my ignorance once more, but it is a difficult concept to grasp. I think I have it, but then find out I don't.

[Swift]

Just wondering why people get riled up about the idea that a dwarf planet is not a planet.

Since this started I've been completely baffled as to why people get riled up about any of this, particularly people who otherwise have almost no interest in astronomy; like Pluto not being called a planet any longer is a personal insult.

There was a recent study that found that the difference between a hydrogen bond and a covalent bond (chemistry) is not as clear cut as thought. I haven't seen the popular press reporting on the uproar among the general public that their beloved hydrogen bond isn't what it used to be.

[Noclevername]

Yeah, we should all be able to interpret newly coined technical terms however we like, irrespective of the definitions given by the people who coined them. That's definitely the way ahead.

Grant Hutchison

If the definition they give doesn't make sense, we should be able to call them on it.

[grant hutchison]

If the definition they give doesn't make sense, we should be able to call them on it.

Sure. But you can't call them on saying "dwarf planets are not planets", because that's a simple matter of defining which set belongs inside which other set, there is no conflict with standard English usage, and they are the sole arbiters of what they meant when they coined the phrase "dwarf planet".
By all means argue over whether their particular choice of definition is a useful one or not (I confess I can't see what important difference it makes whether dwarf planets are, or are not, deemed to be planets); and sure, get yourself bogged down in conflicting definitions of "orbit clearing" if you so desire. My only point is that any attempt to argue that dwarf planets are necessarily planets just because their name includes the word "planet" is doomed to failure under a weight of counterexamples.

Grant Hutchison

[Hornblower]

Yes indeed, a prairie dog is far removed genetically from being a canine. But suppose we substitute "dwarf" for "toy" in classifying a chihuahua, for example. It is too small to dominate a pack of big dogs, but otherwise it is what we commonly consider to be a dog.

[grant hutchison]

Yes indeed, a prairie dog is far removed genetically from being a canine. But suppose we substitute "dwarf" for "toy" in classifying a chihuahua, for example. It is too small to dominate a pack of big dogs, but otherwise it is what we commonly consider to be a dog.

Yes, of course there are many examples in which [adjective+noun] is a subset of [noun]. But it doesn't invalidate the fact that there are also many examples in which [adjective+noun] is not a subset of [noun]. We use metaphor and metonymy frequently when we find new names for things, and not every name of this form can be taken literally.
So there are two coexisting ways in which these pairings can carry meaning--literally or figuratively--and the only way to decide which meaning is intended is to ask the people who coined the phrase.

Grant Hutchison

[PetersCreek]

My apologies but while trying to split the discussion from the poll (they didn't really match up) I lost the poll. Again, my apologies.

[Roger E. Moore]

I surrender. Can someone smart carefully explain what "clearing the neighborhood" means so I know what the IAU was talking about? I really do want to know.

[Hornblower]

I surrender. Can someone smart carefully explain what "clearing the neighborhood" means so I know what the IAU was talking about? I really do want to know.

A large planet will eventually do one of the following to a small body in a similar orbit:

1. Collide with it.
2. Gravitationally eject it into an escape trajectory.
3. Gravitationally lock it into a Trojan orbit, with the same period but 60^o ahead of or behind it.
4. Gravitationally lock it into a resonant orbit that keeps the small body well separated from the major planet.

Neptune is massive enough to dominate Pluto and numerous smaller but similar bodies as in #4. Jupiter causes #3 with numerous asteroids. These bodies in stable orbits near the respective planets total only a tiny fraction of the masses of the planets. Pluto is too small to have such effects on the other stuff in the region of its orbit. They are dominated by Neptune but otherwise orbit with impunity regardless of their separation from Pluto.

These orbital domains are never clear of small stuff at any given time, but the orbits of the small stuff are unstable in the long run except for #3 and #4. Instead of simplistically saying, "A planet has cleared its orbital neighborhood," I think it is better to say, "A planet gravitationally dominates its neighborhood and prevents small bodies from staying in stable orbits except for Trojan or resonant orbits."

[swampyankee]

I have two objections to the term "dwarf planet"; one is that the construct violates normal English usage, in that <adjective> <noun> usually creates a subset, not a distinct class¹ and, two, the separation between "planet" and "dwarf planet" is based on its environment,the vaguely-defined "clearing its orbit,"² instead of the more sensible choice of the object's intrinsic characteristics.

A significant public relations problem with the IAU's decision to set criteria for planets was that they were written very shortly after a large number of large objects, being called (including by professional astronomers) "planets" in what could be considered reaction to the growing number of planets, not out of any previously discussed need to classify these objects as non-planets.

Certainly, the IAU can classify celestial objects; this is not in doubt. Equally, certainly other people, including other scientific groups, can criticize the IAU's classification criteria. This should not be in doubt.

--------------

1: I am quite aware of constructs, such as "prairie dog," which is a compound noun. Nobody redefined some species of animal from "dog" to "prairie dog" (genus Cynomys) as they were never thought to be canids (similarly, no one ever thought that sea robins were birds).

2: Some authors,e. g., Jean-Luc Margot (https://iopscience.iop.org/article/1...6256/150/6/185) have established a numerical criterion, based on object mass and semi-major axis, these also make explicit that the "clearing its orbit" criterion means that two objects, identical except for semi-major axis would be placed in different categories.

[Van Rijn]

So a "prairie dog" is not a dog--it's a thing that lives on the prairie which shares some characteristics with a dog.
Dwarf planet--small object that shares some characteristics with a planet.

I'm not trying to defend the IAU's behaviour on this one, which was at best eccentric. Just wondering why people get riled up about the idea that a dwarf planet is not a planet.

Like Earth shares some characteristics with Jupiter, but they are also very different. Or Neptune, which has similarities to both Jupiter and Earth, but also substantial differences. Then there is Mercury, similar in some ways to Earth, but different. Yet they are all referred to as “planets.”

Dwarf planets share many characteristics with previously recognized planets, but have less mass. It is reasonable to me to consider them a subcategory of planets, but it doesn’t make sense to me to classify them as something somehow so different as to not be planets, given existing examples.

I wouldn’t say that I’m riled up - I don’t feel any great emotion on the subject - but I do and will continue to consider them a subcategory of planets.

I also agree with the OP - there are a number of candidates where enough evidence has been amassed to classify them as dwarf planets, but there doesn’t seem to be a working process to officially recognize them as dwarf planets. That needs to change.

[Roger E. Moore]

A large planet will eventually do one of the following to a small body in a similar orbit:

1. Collide with it.
2. Gravitationally eject it into an escape trajectory.
3. Gravitationally lock it into a Trojan orbit, with the same period but 60^o ahead of or behind it.
4. Gravitationally lock it into a resonant orbit that keeps the small body well separated from the major planet.

Neptune is massive enough to dominate Pluto and numerous smaller but similar bodies as in #4. Jupiter causes #3 with numerous asteroids. These bodies in stable orbits near the respective planets total only a tiny fraction of the masses of the planets. Pluto is too small to have such effects on the other stuff in the region of its orbit. They are dominated by Neptune but otherwise orbit with impunity regardless of their separation from Pluto.

These orbital domains are never clear of small stuff at any given time, but the orbits of the small stuff are unstable in the long run except for #3 and #4. Instead of simplistically saying, "A planet has cleared its orbital neighborhood," I think it is better to say, "A planet gravitationally dominates its neighborhood and prevents small bodies from staying in stable orbits except for Trojan or resonant orbits."

Thank you! I understand now what my problem was earlier in trying to understand this. This makes it very simple.

[skysurfer5cva]

A large planet will eventually do one of the following to a small body in a similar orbit:

1. Collide with it.
2. Gravitationally eject it into an escape trajectory.
3. Gravitationally lock it into a Trojan orbit, with the same period but 60^o ahead of or behind it.
4. Gravitationally lock it into a resonant orbit that keeps the small body well separated from the major planet.

Neptune is massive enough to dominate Pluto and numerous smaller but similar bodies as in #4. Jupiter causes #3 with numerous asteroids. These bodies in stable orbits near the respective planets total only a tiny fraction of the masses of the planets. Pluto is too small to have such effects on the other stuff in the region of its orbit. They are dominated by Neptune but otherwise orbit with impunity regardless of their separation from Pluto.

These orbital domains are never clear of small stuff at any given time, but the orbits of the small stuff are unstable in the long run except for #3 and #4. Instead of simplistically saying, "A planet has cleared its orbital neighborhood," I think it is better to say, "A planet gravitationally dominates its neighborhood and prevents small bodies from staying in stable orbits except for Trojan or resonant orbits."

However, Jupiter gravitationally dominates Saturn's L4 and L5 Lagrange Points. When Jupiter is 60° ahead or behind Saturn, it is closer to Saturn's L4 and L5: ~3.7 AU vs ~9.5 AU. The combination of Jupiter's much closer distance and 3.3x greater mass is what prevents Saturn from maintaining groups of Trojan asteroids.

[profloater]

A large planet will eventually do one of the following to a small body in a similar orbit:

1. Collide with it.
2. Gravitationally eject it into an escape trajectory.
3. Gravitationally lock it into a Trojan orbit, with the same period but 60^o ahead of or behind it.
4. Gravitationally lock it into a resonant orbit that keeps the small body well separated from the major planet.

Neptune is massive enough to dominate Pluto and numerous smaller but similar bodies as in #4. Jupiter causes #3 with numerous asteroids. These bodies in stable orbits near the respective planets total only a tiny fraction of the masses of the planets. Pluto is too small to have such effects on the other stuff in the region of its orbit. They are dominated by Neptune but otherwise orbit with impunity regardless of their separation from Pluto.

These orbital domains are never clear of small stuff at any given time, but the orbits of the small stuff are unstable in the long run except for #3 and #4. Instead of simplistically saying, "A planet has cleared its orbital neighborhood," I think it is better to say, "A planet gravitationally dominates its neighborhood and prevents small bodies from staying in stable orbits except for Trojan or resonant orbits."

Does this mean that Pluto is stable, locked by Neptune.? I ask because the harmonic sequence of orbits is also locked by the gravitational interplay of all planets, so I guess Pluto is different? is a dwarf planet metastable?

[profloater]

I am interested to find about Percival Lowell who predicted the position of Pluto from perturbations of Uranus, and whose initials are immortalised in PL. it transpired his calculations were wrong but his predicted position correct! Another little mystery of coincidence, noting that Pluto had actually been seen earlier but not recognised.

[Roger E. Moore]

Does this mean that Pluto is stable, locked by Neptune.? I ask because the harmonic sequence of orbits is also locked by the gravitational interplay of all planets, so I guess Pluto is different? is a dwarf planet metastable?

Wikipedia says that "Pluto periodically comes closer to the Sun than Neptune, but a stable orbital resonance with Neptune prevents them from colliding."

[grant hutchison]

Does this mean that Pluto is stable, locked by Neptune.? I ask because the harmonic sequence of orbits is also locked by the gravitational interplay of all planets, so I guess Pluto is different? is a dwarf planet metastable?

Stability is a relative term--some resonant orbits are effectively stable for the lifetime of the solar system so far, and some are not. So what we currently see are the survivors of a winnowing process, which have found a "stability niche".
The plutino population is gradually shifting into a particular type of resonance called Kozai resonance, where there's a regular trade-off between eccentricity and inclination--Kozai introduces greater stability, so tends to "trap" objects that drift into that dynamical zone. So there's an expectation that the Kozai population will rise at the expense of the non-Kozai population, a process that is still on-going.

Grant Hutchison

[profloater]

Stability is a relative term--some resonant orbits are effectively stable for the lifetime of the solar system so far, and some are not. So what we currently see are the survivors of a winnowing process, which have found a "stability niche".
The plutino population is gradually shifting into a particular type of resonance called Kozai resonance, where there's a regular trade-off between eccentricity and inclination--Kozai introduces greater stability, so tends to "trap" objects that drift into that dynamical zone. So there's an expectation that the Kozai population will rise at the expense of the non-Kozai population, a process that is still on-going.

Grant Hutchison

Thanks, that isexactly what I wantedto know.

[swampyankee]

One problem is that the stability criteria commonly used to determine the stability of systems, such as the Lyapunov or Routh-Hurwitz, don't work all that well for gravitationally-bound systems; this means it's impossible to prove that a system is stable if there are more than a few (probably two) objects of significant mass in the system. While numerical simulations of the Solar System tend to show stability over multi-billion year scales, this is not the same.