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IAU Standard for Planets is Not Supported in Research Literature

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#26 russell23

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Posted 29 August 2019 - 07:00 PM

I'm not technically opposed to hundreds of planets (which is latest tack Stern, etc. are taking, having recognized that nine is _never_ again going to fly).  Just opposed to nine, which makes the least technical sense of any alternative.

 

You have an incorrect understanding of Stern's views on this.  Here is really good read on planetary classification (Stern & Levison 2002):

 

http://articles.adsa...HiA....12..205S

 

Certainly as of 2002 Stern was proposing there are many more than 9 planets.  In the paper linked to above he defined the following types of objects:

 

Planetary body --> Condensing what was written in the paper: a body that is massive enough to be shaped by gravity into a spheroidal shape but not so massive that it has ever has core nuclear fusion (not a brown dwarf or star).

 

Stern & Levison then define the following terms:

 

Planet, planetary scale satellite, unbound planet

 

Planet is defined as follows in the paper:  "A planet is any planetary body on a bound orbit around a single or multiple star system; by our definition, the classical 9 planets, as well as a few of the largest asteroids, and very large KBO's, qualify."

 

So in 2002 Stern & Levison were proposing many more than 9 planets.  I'm not sure where you are getting the idea that Stern wants, or has ever wanted just 9 planets.  But that is not the case.

 

Another important thing this paper gets into which the IAU really botched is an understanding of sub-types.    Stern & Levison discuss dynamical classification and make the distinction that the IAU later defined as planets and dwarf planets.  A dynamical dominance definition did not first come with the IAU.  Stern & Levison proposed it in 2002.  From section 6 of their paper:

 

Stern&Levison 2002:  Our goal for a dynamical classification scheme is thus to determine whether any given body is dynamically important to the system in which it is found.  Hence, we define and uberplanet as a planetary body in orbit about a star that is dynamically important enough to have cleared its neighboring planetesimals in a Hubble time.  And we define an unterplanet as one taht has not been able to do so.  It is important to note that, unlike the physical criteria for planethood, these purely dynamical criteria cannot be an intrinsic aspect of a body, but is necessarily dependent on the environment and dynamical context in which a body finds itself."

 

What Stern&Levison proposed in 2002 is basically what the IAU did.  Uberplanets are IAU planets and unterplanets are IAU dwarf planets.  But there is an important distinction which is the reason for the controversy.  The IAU decreed that dwarf planets are not a type of planet. 

 

Stern & Levison's paper illustrated the taxonomic idea of a broad category and sub-types that is lacking in the IAU system. 

 

Now you have said that you do not object to hundreds of planet, but just to nine.  Since I cleared up above that Stern is not proposing 9 - and never did, I'd like to ask what objections you might have to what I have proposed.  Here they are:

 

Brown dwarf:  Sub-stellar mass body (<~60 Jupiter masses) formed by star-like gas collapse mechanisms that did not acquire sufficient mass to sustain core hydrogen fusion.

 

Planet:  Sub-stellar mass body formed in a proto-planetary disk with sufficient mass to self-gravitate into a spheroidal shape.

 

Dynamical Classes of Planets:

 

Principal planet:  planet orbiting a star or brown dwarf that dynamically dominates its orbit (IAU planets)

 

Belt planet:  Planet orbiting a star or brown dwarf that does not dynamically dominate its orbit and therefore shares its orbit with numerous bodies that have a combined mass greater than the mass of the belt planet.

 

Satellite planet:  planet with orbiting a larger planet.

 

Satellite/moon: sub-stellar mass body formed in a proto-planetary disk in orbit around a planet or dwarf planet with insufficient mass to self-gravitate into a spherical shape

 

Rogue planet:  planet without an orbit around a star.   Since this type of body must have formed in a proto-planetary disk it has been ejected from its orbit.

 

A useful aspect of the above definitions is that they are compatible with a body changing dynamical circumstances. 

 

Examples:

 

~1.  A belt planet is captured into an orbit around a principal planet and therefore its dynamical class shifts from belt planet to satellite planet.  An example of this is Neptune's large Satellite Triton, which is a very Pluto-like body Neptune captured from the Kuiper belt.  At one time in its history it was a belt planet.  Now it is a satellite planet.

 

~2.  A principal planet, belt planet, or satellite planet is ejected from its orbit and no longer orbits a star.  It has now become a rogue planet.

 

~3.  Migration of a principal planet's orbit shifts it outward into the Kuiper belt where it no longer is more massive than the combined mass of the other bodies in its orbital zone.  The dynamical class has shifted from principal planet to belt planet. 

 

I did not address the concept of "double-planet" or "double-dwarf planet" but neither has the IAU.  However, I did address that concept and much of the above in this paper:

 

http://www.scirp.org...x?paperid=81133

 

Take some time to analyze all this and let me know if you can think of any arguments why the IAU definitions are more useful than what I have described.


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#27 Mister T

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Posted 30 August 2019 - 08:15 AM

I think NONE of the current planets should be planets!!

graduate.sml.gif 

since they are all in stable orbits, none of them are wanderers. thus undeserving of the name.

If we're gonna argue/ partake in heated debate, then lets at least use the correct meaning!

shocked.gif


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#28 bobzeq25

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Posted 30 August 2019 - 01:27 PM

You have an incorrect understanding of Stern's views on this.  Here is really good read on planetary classification (Stern & Levison 2002):

 

http://articles.adsa...HiA....12..205S

 

Certainly as of 2002 Stern was proposing there are many more than 9 planets.  In the paper linked to above he defined the following types of objects:

 

Planetary body --> Condensing what was written in the paper: a body that is massive enough to be shaped by gravity into a spheroidal shape but not so massive that it has ever has core nuclear fusion (not a brown dwarf or star).

 

Stern & Levison then define the following terms:

 

Planet, planetary scale satellite, unbound planet

 

Planet is defined as follows in the paper:  "A planet is any planetary body on a bound orbit around a single or multiple star system; by our definition, the classical 9 planets, as well as a few of the largest asteroids, and very large KBO's, qualify."

 

So in 2002 Stern & Levison were proposing many more than 9 planets.  I'm not sure where you are getting the idea that Stern wants, or has ever wanted just 9 planets.  But that is not the case.

 

Another important thing this paper gets into which the IAU really botched is an understanding of sub-types.    Stern & Levison discuss dynamical classification and make the distinction that the IAU later defined as planets and dwarf planets.  A dynamical dominance definition did not first come with the IAU.  Stern & Levison proposed it in 2002.  From section 6 of their paper:

 

 

 

 

What Stern&Levison proposed in 2002 is basically what the IAU did.  Uberplanets are IAU planets and unterplanets are IAU dwarf planets.  But there is an important distinction which is the reason for the controversy.  The IAU decreed that dwarf planets are not a type of planet. 

 

Stern & Levison's paper illustrated the taxonomic idea of a broad category and sub-types that is lacking in the IAU system. 

 

Now you have said that you do not object to hundreds of planet, but just to nine.  Since I cleared up above that Stern is not proposing 9 - and never did, I'd like to ask what objections you might have to what I have proposed.  Here they are:

 

Brown dwarf:  Sub-stellar mass body (<~60 Jupiter masses) formed by star-like gas collapse mechanisms that did not acquire sufficient mass to sustain core hydrogen fusion.

 

Planet:  Sub-stellar mass body formed in a proto-planetary disk with sufficient mass to self-gravitate into a spheroidal shape.

 

Dynamical Classes of Planets:

 

Principal planet:  planet orbiting a star or brown dwarf that dynamically dominates its orbit (IAU planets)

 

Belt planet:  Planet orbiting a star or brown dwarf that does not dynamically dominate its orbit and therefore shares its orbit with numerous bodies that have a combined mass greater than the mass of the belt planet.

 

Satellite planet:  planet with orbiting a larger planet.

 

Satellite/moon: sub-stellar mass body formed in a proto-planetary disk in orbit around a planet or dwarf planet with insufficient mass to self-gravitate into a spherical shape

 

Rogue planet:  planet without an orbit around a star.   Since this type of body must have formed in a proto-planetary disk it has been ejected from its orbit.

 

A useful aspect of the above definitions is that they are compatible with a body changing dynamical circumstances. 

 

Examples:

 

~1.  A belt planet is captured into an orbit around a principal planet and therefore its dynamical class shifts from belt planet to satellite planet.  An example of this is Neptune's large Satellite Triton, which is a very Pluto-like body Neptune captured from the Kuiper belt.  At one time in its history it was a belt planet.  Now it is a satellite planet.

 

~2.  A principal planet, belt planet, or satellite planet is ejected from its orbit and no longer orbits a star.  It has now become a rogue planet.

 

~3.  Migration of a principal planet's orbit shifts it outward into the Kuiper belt where it no longer is more massive than the combined mass of the other bodies in its orbital zone.  The dynamical class has shifted from principal planet to belt planet. 

 

I did not address the concept of "double-planet" or "double-dwarf planet" but neither has the IAU.  However, I did address that concept and much of the above in this paper:

 

http://www.scirp.org...x?paperid=81133

 

Take some time to analyze all this and let me know if you can think of any arguments why the IAU definitions are more useful than what I have described.

I _greatly_ respect your thoughtful, well referenced, peer reviewed paper on this.  You are clearly better qualified than me.

 

Personally, for me, it's really simple.  I personally prefer 8 planets to many, including some asteroids, some moons.  I like that taxonomy.  I think the "the IAU said dwarf planets are not planets" thing is way overblown.  Just semantics.

 

My proposal is to let the IAU take another crack at it, considering explicitly the many planets option, and allowing time for thoughtful debate.


Edited by bobzeq25, 30 August 2019 - 01:33 PM.


#29 llanitedave

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Posted 31 August 2019 - 11:43 AM

The issues you raise about biology are definitely real, but I feel they are really shortcomings in our knowledge about past events, and in our attempts to impose species labels near branch points, where they don't belong.

To the second point, the tree structure doesn't just tell you the correct taxon for a lifeform. It also shows you where taxons merge, and insistence on discrete names doesn't work

So in the Neanderthal/Denisovan situation, the 'correct' answer is that you can't discretely name them at that point, as they are not yet discrete species.

Just because there is a correct taxonomy doesn't mean it's going to be easy to identify, understand or apply.

Ring species are a good example of this (good explanation in Wikipedia). Applying names to them coherently is impossible. But the problem isn't the reality of the evolutionary relationships, which are perfectly clear. The problem is a linguistic one where we insist on naming things as different species or the same species, while reality is very clearly telling us neither is the case.

I think this is fundamentally different from what is going on when we name astrophysical objects.

I agree with all of this except the last sentence, and that one is only a mild dispute.  While I agree that a taxonomy of planetary bodies would not be the same kind of tree structure as that useful for living things, I don't think the differences are all that fundamental.  The purpose and the utility is the same, if properly done it gives us insights and tools for exploration and analysis that we wouldn't have easy access to otherwise.



#30 Adun

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Posted 31 August 2019 - 02:23 PM

After recently becoming a birder, I found quite interesting the utter disregard many birders (and authors) have for taxonomers.

 

Not being a professional scientist, I don't really know what does it mean that the IAU decrees something. I had not heard about the IAU before the whole Pluto thing.

 

My understanding is that what prompted the whole strife and discord was not animosity towards Pluto, but instead the 2004-2005 rapid discoveries of (aptly named) Eris, Makemake and Haumea, with the prospect of more to come.

 

The whole trans-neptunian-ness of their orbits seems to be the main reason for the new classification, just like the discovery of other (smaller) rocks led to de demotion of Ceres to "asteroid" back in 1851 (after half a century of being classified as a "planet"). However, it's odd that the new classification promotes Ceres back to (dwarf) planet after a century and a half of having being just an asteroid. It gives a smell: the taxonomy was very wrong before, or is wrong now. It speaks of how little we know, and I bet if (when) we get a chance to better see other star systems, we'll probably come up with a different taxonomy.

 

This reminds me of something said by an author (of birding field guides) whom I know, who says that (bird) taxonomers are often wrong because they classify birds using skins in a museum, instead of seeing/hearing/observing the actual living beings.

 

For me though,  a dwarf planet is still a planet, just as much as a red dwarf is still a star.

 

So, for me, Pluto, Eris, Ceres, Makemake, and Haumea are all planets.

 

In a few billion years, after the Sun becomes a red giant and eats up Mercury, Venus, and Earth, the Sun's core will collapse, leaving it's outer atmosphere out there, a.k.a. a Planetary nebula. When that happens, whatever's left of Jupiter better get busy clearing it's orbit again, ┬┐right?


Edited by Adun, 31 August 2019 - 02:33 PM.


#31 llanitedave

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Posted 31 August 2019 - 03:37 PM


This reminds me of something said by an author (of birding field guides) whom I know, who says that (bird) taxonomers are often wrong because they classify birds using skins in a museum, instead of seeing/hearing/observing the actual living beings.

 

That used to be true, and it did lead to a lot of errors.  Today, classification is more properly done with DNA, when possible.  My son-in-law is an ornithology major, who's knowledge of and passion for birds, especially raptors, long predates his formal schooling.  We've discussed several times how confusing bird morphology can be.



#32 Mister T

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Posted 08 September 2019 - 10:05 AM

Not to bring up an old subject, but...

If people are so upset about Pluto being demoted the how come NO ONE  is upset about Indigo not being a color anymore???

It's ROY G. BIV not BV ****!



#33 llanitedave

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Posted 08 September 2019 - 02:50 PM

Not to bring up an old subject, but...

If people are so upset about Pluto being demoted the how come NO ONE  is upset about Indigo not being a color anymore???

It's ROY G. BIV not BV ****!

When did this happen?  Now I'm scandalized!



#34 Mister T

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Posted 09 September 2019 - 06:10 AM

Totally Unacceptable!!



#35 sg6

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Posted 09 September 2019 - 09:38 AM

As Alan Stern says, "... if you put Earth where Pluto is, it would be excluded!"

Makes sense as it would therefore be in an path/track/orbit where it had not cleared its orbit. So yes it would fail the definition of a planet.

 

If you put the earth around another star it would be an exoplanet to whoever was left here.

 

The statement seems almost strange, in effect Pluto is just made the size of the earth, however being in an uncleared orbit it fails the definition of "Planet", as size is just one of 4 requirements. A somewhat big dwarf planet foreheadslap.gif question.gif



#36 russell23

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Posted 09 September 2019 - 10:38 AM

Makes sense as it would therefore be in an path/track/orbit where it had not cleared its orbit. So yes it would fail the definition of a planet.

 

If you put the earth around another star it would be an exoplanet to whoever was left here.

 

The statement seems almost strange, in effect Pluto is just made the size of the earth, however being in an uncleared orbit it fails the definition of "Planet", as size is just one of 4 requirements. A somewhat big dwarf planet foreheadslap.gif question.gif

The determination of mass needed to clear an orbit has been refined.   The recent analysis by Margot (2015) is interesting.  According to Margot the Earth would still be massive enough to clear the orbital zone of Pluto (and Eris) so Earth would still be a planet.  However, Mercury would not be a planet in the orbit of Neptune and further.  Mars would not be a planet in the orbit of Pluto and further. 

 

But Pluto is massive enough to meet the planet definition at the orbit of Earth. 

 

This is what Stern and similar thinking people object to -  an object being a planet if it orbits the star "there", but not a planet if it orbits the star "there".   What I described in post #26 gets around that problem.  All spherical sub-stellar bodies formed in a proto-planetary disk are planets and then you divide planets into dynamical classes.  The IAU definitions cover two of the four dynamical classes. 



#37 llanitedave

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Posted 10 September 2019 - 09:45 AM

Makes sense as it would therefore be in an path/track/orbit where it had not cleared its orbit. So yes it would fail the definition of a planet.

 

If you put the earth around another star it would be an exoplanet to whoever was left here.

 

The statement seems almost strange, in effect Pluto is just made the size of the earth, however being in an uncleared orbit it fails the definition of "Planet", as size is just one of 4 requirements. A somewhat big dwarf planet foreheadslap.gif question.gif

Planet/exoplanet isn't really a valid distinction, any more than is saying Americans=humans and non-Americans=exohumans.

 

And yes, the fact that Earth would fail the planet test if placed in Pluto's orbit is exactly the point of this discussion.  That illustrates why the current definition is flawed.  The location of a body in its orbit is not an intrinsic characteristic of that body, since orbits can change.

 

If you move a U.S. citizen to China, are they no longer human?



#38 David E

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Posted 21 September 2019 - 08:53 PM

 

One of these things is not like the others
One of these things just doesn't belong...

 

Planet  Ecc.      Inc. (┬░ to invariable plane)
Mer     0.205     6.34
Ven     0.007     2.19
Ear     0.017     1.57
Mar     0.093     1.67
Jup     0.049     0.32
Sat     0.057     0.93
Ura     0.046     1.02
Nep     0.009     0.72
Plu     0.249     15.6

 

I know that eccentricity and inclination weren't even part of the IAU definition, but Pluto's have annoyed me since I first saw models of the solar system at age seven. Good riddance! (And watch your step, Mercury, you're looking pretty shaky too.)

hmm.gif

 

That would be Jupiter. It's the only planet with a number less than .5. 



#39 David E

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Posted 21 September 2019 - 08:59 PM

FarmerRon.gif

 

Pluto:

Is round;

Has an atmosphere;

Is geologically active;

Has more moons than all the other rocky planets combined;

Spends a good portion of it's time inside the orbit of Neptune, causing it to deviate from it's orbit;

Is subject to global warming;

 

Yep! It's a planet! jump.gif




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