Is Pluto about to be reinstated as a planet?

[Roger E. Moore]

[reads through whole thread] Wait a minute, is all the recent hype just the OLD hype being recycled, or is there something new coming?

[01101001]

I think some of the cites were to old news, like Alan Stern's IAU objections.

My sense is what's new is this geology student and friends pushing for a geological definition, not one by the astronomers: Sad About Pluto? How about 110 Planets in the Solar System Instead?

Their study – titled “A Geophysical Planet Definition“, which was recently made available on the Universities Space Research Association (USRA) website – addresses what the team sees as a need for a new definition that takes into account a planet’s geophysical properties.

So it's not about overthrowing the IAU definition. It's not about reinstatement. Is he going to submit it to IAU?

No. Because the assumption there is that the IAU has a corner on the market on what a definition is. We in the planetary science field don’t need the IAU definition.

[Roger E. Moore]

Here is the proposal. Will take some time to look it over and comment later.

http://www.hou.usra.edu/meetings/lpsc2017/pdf/1448.pdf

[agingjb]

It looks like a proposal that recognises that the intrinsic properties of an object are at least interesting as what and where it orbits. The problem, for me, with "planet" is that current definitions don't characterise a class worthy of exclusive study. No, I don't know what to call the wider class.

[rtroxel]

NASA is now officially on board with the movement to designate Pluto a full-fledged planet again:


http://www.usatoday.com/story/tech/n...gain/98187922/

[Amber Robot]

NASA is now officially on board with the movement to designate Pluto a full-fledged planet again:


http://www.usatoday.com/story/tech/n...gain/98187922/

Not sure about that. Alan Stern is not a NASA employee. And the article doesn't specify who his "colleagues" are. I wouldn't characterize this as "NASA is now officially on board".

[01101001]

NASA is now officially on board with the movement to designate Pluto a full-fledged planet again:

http://www.usatoday.com/story/tech/n...gain/98187922/

And USA Today is just regurgitating the Gizmodo article: NASA Scientists Have a Plan to Make Pluto a Planet Again, and the Gizmodo article subsequently made a huge retraction:

Correction: Kirby Runyon, first author on the new planet definition LPSC abstract, informs us that the proposal is not being submitted to the International Astronomical Union as has been reported elsewhere. The article has been updated to correct this error.

Some reporting about this LPSC Geophysical proposal has been abysmal.

It isn't about Alan Stern. It isn't about the IAU or the IAU definition. It isn't about NASA. And it's only 1% about Pluto.

[Roger E. Moore]

For some reason this argument reminds me of the time we had a sixth Great Lake.

http://www.nytimes.com/1998/03/07/us...reat-lake.html

[danscope]

Why it's the biggest little lake we've got !!!

[DonM435]

Attempted embiggening, I'd say.

[Roger E. Moore]

https://arxiv.org/pdf/1603.08614.pdf
PROBABILISTIC FORECASTING OF THE MASSES AND RADII OF OTHER WORLDS
Jingjing Chen and David Kipping (2017)

The above very-new paper proposes a new system of organizing exoplanets such that there is no distinction made between dwarf planets and terrestrial ("terran") planets so long as they are round; no distinction between Neptune, Uranus, and Saturn except in size; and no distinction between Jupiter and brown dwarfs except in mass.

Just felt like throwing gasoline on the fire,

[swampyankee]

It looks like a proposal that recognises that the intrinsic properties of an object are at least interesting as what and where it orbits. The problem, for me, with "planet" is that current definitions don't characterise a class worthy of exclusive study. No, I don't know what to call the wider class.

Perhaps the geologists and planetary scientists will embrace the concept of hierarchy, as in biological taxonomy.

Here is the proposal. Will take some time to look it over and comment later.

http://www.hou.usra.edu/meetings/lpsc2017/pdf/1448.pdf

I think the worst possible outcome would be for planetary scientists and astronomers to come up with contradictory categories for the same physical objects. This sort of contradictory nomenclature has happened.

[01101001]

Upon hearing of this new proposal, a certain Bad Astronomer offered up his usual opinion.

Bad Astronomy | Redefining planets: An answer in search of a question

And therein lies my basic problem with all this. I’m OK with this new idea, but not if it’s called a definition! That may seem like semantics, but it’s important: Nature very rarely has vividly defined borders, even if we humans like to have them. But when we make them, they tend to be arbitrary, like defining “green”. And when you get near the borders, things get fuzzy, indeed.

[Canis Lupus]

And therein lies my basic problem with all this. I’m OK with this new idea, but not if it’s called a definition! That may seem like semantics, but it’s important: Nature very rarely has vividly defined borders, even if we humans like to have them. But when we make them, they tend to be arbitrary, like defining “green”. And when you get near the borders, things get fuzzy, indeed.

And therein rests my basic problem with all that which preceded "all this".

Accepting the futility of vacuum tight definitions, what then do we rely upon? To my way of thinking Pluto as a fully fledged Planet served us nobly for a multitude of reasons. In return, we repaid the service with a demotion. If Pluto was an employee, it would have been "employee of the month" ... nay, "of the century!" I almost weep at the ingratitude of my fellow humanoids.

Dear Pluto, if somehow you can read these words, know that I, and a great many other life-forms here on Earth (third rock from Sun), regard you with considerable affection and admiration. If it was up to me, I would classify you as a "Super-Dooper Planet".

[Canis Lupus]

If you want to use these new ideas and call Pluto a planet, that’s fine. But then, explore why we think of it that way, and why it’s different from, say, Jupiter.
Definitions are an endpoint. Concepts are a starting point. I prefer the latter.

http://www.blastr.com/2017-2-21/redefining-planets-answer-search-question

Agreed, and taking on this line of thought's implication, there is a suggestion that the impossibility of defining a "planet" (whatever that thing may be) is suggestive of an inadequate model in which that indefinable thing exists. In other words, the reason for the impossibility is that thing we are dealing with, trying to define, exists within a model which makes it impossible to define. Our model is the problem. Correct it and the thing we are discussing becomes easily defined.

When I saw the logic, I was surprised, but it is a clear enough implication and explanation for the difficulties being experienced.

[Canis Lupus]

Despite the above suggestion, and several others I have read, having some merit, I'm not sure if Science necessarily wants to resolve the situation regarding the classification of Pluto. Amongst the young, those that Science wishes to enthrall, it arouses a little passion, which isn't a bad thing for a longer term interest in Science.

[lpetrich]

The IAU's decision: Pluto and the Solar System | IAU

A celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

The recent proposal to reinstate Pluto: A Geophysical Planet Definition

A planet is a sub-stellar mass body that has never undergone nuclear fusion and that has sufficient self-gravitation to assume a spheroidal shape adequately described by a triaxial ellipsoid regardless of its orbital parameters.

This implies that the Solar System has over 100 planets, and that some planets' moons are also planets. Like the Earth's Moon.

I propose an alternate name for an object in approximate hydrostatic equilibrium: "orb".

Some of these would-be planets:

Every round object in the solar system under 10,000 kilometers in diameter, to scale | The Planetary Society: Mars, Ganymede, Titan, Mercury, Callisto, ...

[lpetrich]

I will now estimate the maximum size of an irregularly-shaped object. This I will do by estimating the maximum height of a mountain on an orb. If the mountain's size is the orb's size, then the orb can have an irregular shape. That height is limited by the yield strength of the materials that it is composed of., Pmax. The pressure at the base of a mountain with height h is approximately den*g*h where g is the acceleration of gravity, and (den) is the mountain material's mass density. Thus,

h = Pmax/(den*g)

In the constant-density, spherical limit, g = G*M/R² = (4*pi/3)*G*den*R

where G is the Newtonian gravitational constant. Thus, after omitting numerical factors near 1,

h = Pmax/(G*den²*R)

So the height of the tallest mountain is inversely proportional to the orb's radius. There will be a certain radius where they are equal. Smaller than that, and the object can have an irregular shape.

For the Solar System, after scaling for gravity, the highest mountains Mauna Kea and Mauna Loa in Hawaii. They are about 10.3 km above their surroundings, the nearby ocean floor. Olympus Mons on Mars is higher in absolute numbers, 21 km, but scaled to the Earth's gravity, it is about 8.5 km.

From h = R for those Hawaiian mountains, I find a radius of 260 km, around the radius of Vesta. However, the tallest feature on that asteroid is the central peak in its crater Rheasilvia, a peak that rises some 20 - 25 km/s above its surroundings. This gives a h = R size of 72 to 81 km.

So 100 km may be a good boundary radius.

[Canis Lupus]

A planet is a sub-stellar mass body that has never undergone nuclear fusion and that has sufficient self-gravitation to assume a spheroidal shape adequately described by a triaxial ellipsoid regardless of its orbital parameters.

Problem I have with this definition is I'm not convinced that planets, including Earth, don't undergo some type of nuclear fusion at the core. I'd say the more massive the planet, the more likely it is to undergo some type of nuclear fusion.

Mars might be considered a planet too small for such a reaction or too limited having exhausted fuel, whereas Venus might be considered as one which lacked stabilizing factors to control the reaction. The end effect being a runaway burn of energy now exhausted. Venus, like Mars, is now exhausted but having burnt a lot more fuel than Mars, has been left with a big pollution problem.

Perhaps Earth represents a long standing balance of the reaction to date and for the time being.

[Canis Lupus]

The other problem is "sub-stella mass". We have theories for what we think is the smallest mass for a star, but observation confirming these calculations is another issue.

[Canis Lupus]

Perhaps Mercury is the mass which needs redefining to the status of a type of spent proto-planet. What happened to it, apart from meteorite bombardment, is a mystery thanks to the evidence being scorched by the solar wind. All that's left, and has been left for some time, is probably a spent core of a planet.

There may also be a case for categorizing Jupiter, Saturn, Uranus and Neptune as proto-planets similar to the standard definition of proto-planet in that a solid core may be still be forming from a nuclear reaction under intense pressure. Planet formation right under our noses, in the last place we expected to see it. The "giants" didn't fail to surprise the Voyager "crew", and they may still be working their magic - I'm reminded of the saying, "smoke and mirrors".

Looked at this way, Pluto appears to be more a planet than the really big boys ironically, as do some other "dwarfs" perhaps.

[Canis Lupus]

Problem I have with this definition is I'm not convinced that planets, including Earth, don't undergo some type of nuclear fusion at the core. I'd say the more massive the planet, the more likely it is to undergo some type of nuclear fusion.
...

Here we go, some peer reviewed literature to back it up ...

The cause and source of the heat released from Earth’s interior have not yet been determined. Some research groups have proposed that the heat is supplied by radioactive decay or by a nuclear georeactor. Here we postulate that the generation of heat is the result of three-body nuclear fusion of deuterons confined in hexagonal FeDx core-centre crystals; the reaction rate is enhanced by the combined attraction effects of high-pressure (~364 GPa) and high-temperature (~5700 K) and by the physical catalysis of neutral pions: 2D + 2D + 2D → 21H + 4He + 2  + 20.85 MeV. The possible heat generation rate can be calculated as 8.12 × 1012 J/m3, based on the assumption that Earth’s primitive heat supply has already been exhausted. The H and He atoms produced and the anti-neutrino are incorporated as Fe-H based alloys in the H-rich portion of inner core, are released from Earth’s interior to the universe, and pass through Earth, respectively.

https://www.nature.com/articles/srep37740

It's always a nice feeling when you think these things first and then go out and find support. It doesn't prove anything, of course, but does give a slight sense the thinking is going along the right track.

[Canis Lupus]

Just as an aside, and by way of an observation that may one day prove very significant I hope: the three planets (Mercury, Venus and Mars, those that appear most likely to have spent their nuclear reaction, if such reactions occur) are the only planets which do not have moons, if you disregard the "potatoes" orbiting Mars.

[Canis Lupus]

More of a test post for the upload of an image as anything else

Figure: Substoichiometric FeDx crystal with all octahedral D sites (small red circles) and all tetrahedral vacancy sites (small yellow circles) in an Fe (large white circles) hexagonal close-packed (hcp) lattice at 332 GPa and 4820 K near the inner core centre.

https://www.nature.com/articles/srep37740

[Ericlobster]

Definition of a planet: A celestial body moving in orbit around a star? Does Pluto qualify? Then despite what some 'purist' scientists have to say, Pluto is a planet.

[BigDon]

Lupus' post #112

The quote states their assumptions are based on the Earth already exhausting its primordial heat of formation. I'm given to understand that at least 40% of that original heat is still with us.

How am I supposed to reconcile this dichotomy?

[Amber Robot]

Definition of a planet: A celestial body moving in orbit around a star? Does Pluto qualify? Then despite what some 'purist' scientists have to say, Pluto is a planet.

Is there a different kind of body, other than celestial, that might orbit a star?

How are you defining "celestial body"?

[Swift]

Definition of a planet: A celestial body moving in orbit around a star? Does Pluto qualify? Then despite what some 'purist' scientists have to say, Pluto is a planet.

Comets? Asteroids?

[swampyankee]

Comets? Asteroids?

Put a numerical lower mass limit on planets, and define asteroids and comets by composition.

[Swift]

Put a numerical lower mass limit on planets, and define asteroids and comets by composition.

Ganymede and Titan mass more than Mercury. Callisto, Io, our Moon, Europa, Triton, and Eris all mass more than Pluto. Are they planets? What is the value for this lower mass limit and what is it based on? Pluto masses 1.3 x 10²² kg, is that the limit, and if so, why that value?

My understanding of comets and asteroids is that the compositions are highly variable and even the difference between a comet and an asteroid is blurry - how do you define such that Ceres is not a planet, or should it be?

I'm not picking on you, nor am I favoring or arguing against any of these definitions. But I think a lot of people act like it is easy to come up with some definition, and that the IAU somehow missed some easy, obvious definition. I'm saying it is a lot harder.

I'm also saying that if your entire goal is to make Pluto a planet (a goal I completely fail to understand), then you are going to have to open it open to a lot of objects that were not traditionally planets.