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rtroxel
2014-Oct-03, 01:21 PM
Some astronomers at Harvard think it's a planet:
http://www.techtimes.com/articles/17093/20141003/yes-no-harvard-astronomers-kick-up-storm-by-claiming-pluto-is-indeed-a-planet.htm


Also...One of the reasons Pluto is not considered a planet by some observers, is because there is debris in its orbit that has not become part of the planet itself. As it turns out, however, Jupiter has a similar problem:

http://www.exploremars.org/trojan-asteroids-around-jupiter-explained

Roy

NEOWatcher
2014-Oct-03, 02:09 PM
No, no and no.
That's been going around so much that the mainstream is debunking it.

If it doesn't involve the IAU, then it's not true. They are the ones who started the mess in the first place.

Even though most people want Pluto to be a planet, a lot of this latest hype is due to publicity of New Horizons.

Hlafordlaes
2014-Oct-03, 02:23 PM
What really seems out of date is the old classification system. We now have to add gas dwarfs* (http://www.fromquarkstoquasars.com/meet-the-newest-classification-for-planets-the-gas-dwarf/), apparently.

* Spelling rules for dwarfs/dwarves (http://grammarist.com/usage/dwarfs-dwarves/).

NEOWatcher
2014-Oct-03, 02:43 PM
What really seems out of date is the old classification system. We now have to add gas dwarfs* (http://www.fromquarkstoquasars.com/meet-the-newest-classification-for-planets-the-gas-dwarf/), apparently.
There's one thing in that article that infuriates me. Who is "the team"? The Kepler team? The people at the Harvard center?
It's bad enough when an reporter starts using indefinite articles before describing them, but this one doesn't even do that.

Rant aside. It is an interesting finding that there is a definite difference at those sizes.

Buttercup
2014-Oct-03, 02:46 PM
Wasn't its demotion a certain scientist's vainglorious attempt at being highly recognized for something?

I wish Pluto would be reinstated as a planet.

iquestor
2014-Oct-03, 02:56 PM
I for one am really looking forward to New Horizon's flyby next July :)

Buttercup
2014-Oct-03, 03:15 PM
I for one am really looking forward to New Horizon's flyby next July :)

Me too!! :) I read an article last year - speculation that Pluto might have 10 moons. Wouldn't that be awesome? :)

Amber Robot
2014-Oct-03, 05:09 PM
Also...One of the reasons Pluto is not considered a planet by some observers, is because there is debris in its orbit that has not become part of the planet itself. As it turns out, however, Jupiter has a similar problem:

http://www.exploremars.org/trojan-asteroids-around-jupiter-explained

Roy

That's a bit of a mischaracterization. The phrase "cleared the neighborhood" in the IAU definition is not the best choice of words, but the gist of it is that Pluto is a member of a population of objects sharing similar orbits and similar properties (and possibly similar formation mechanisms). This is not true for Jupiter or any of the other major planets.

Hlafordlaes
2014-Oct-03, 05:56 PM
That's a bit of a mischaracterization. The phrase "cleared the neighborhood" in the IAU definition is not the best choice of words, but the gist of it is that Pluto is a member of a population of objects sharing similar orbits and similar properties (and possibly similar formation mechanisms). This is not true for Jupiter or any of the other major planets.

How about this, Buttercup? Pluto has gone from being the least in its class to arguably the most important. It's a promotion!

Amber Robot
2014-Oct-03, 07:07 PM
How about this, Buttercup? Pluto has gone from being the least in its class to arguably the most important. It's a promotion!

Well, that is certainly a more optimistic view of the "demotion" of Pluto than most people put on it.

Whatever we call it, it is still the same, and it is still an interesting object to study.

Buttercup
2014-Oct-03, 07:08 PM
How about this, Buttercup? Pluto has gone from being the least in its class to arguably the most important. It's a promotion!

Hmmm. An interesting thought, but I'm not quite sold on it.

Would still like to trip that scientist (as he's walking down a hallway or whatever). :p

Amber Robot
2014-Oct-03, 08:52 PM
I wonder how many people got their panties in a twist when Ceres was demoted to asteroid after being a planet for 50 or so years.

Buttercup
2014-Oct-03, 10:47 PM
I wonder how many people got their panties in a twist when Ceres was demoted to asteroid after being a planet for 50 or so years.

Noted.

Hornblower
2014-Oct-04, 02:46 PM
The IAU should not let general public opinion, much of it poorly informed scientifically, stampede them into nullifying the reclassification. It would be a good idea to revise the wording of the "clearing" criterion to stop the erroneous interpretation of it as excluding Jupiter.

primummobile
2014-Oct-04, 06:56 PM
I'm not sure why people call it a demotion anyway. It's a change in classification and that's it. We invented a term that better described what Pluto actually is and that's what we call it now.

DonM435
2014-Oct-04, 08:00 PM
As one wise man suggested, aliens surveying our solar system might well note: "Yellow star: Four planets plus debris."

CJSF
2014-Oct-07, 09:23 PM
Wasn't its demotion a certain scientist's vainglorious attempt at being highly recognized for something?

Mike Brown? While he takes a certain amusement in poking fun at the whole thing (calling himself Pluto killer and etc.), the reclassification of Pluto was not done on his bidding or input. His (and others') discoveries of other objects out in that neck of the solar system were catalysts, is all. I don't find him remotely "vainglorious."

CJSF

Amber Robot
2014-Oct-07, 09:28 PM
As one wise man suggested, aliens surveying our solar system might well note: "Yellow star: Four planets plus debris."

Only if those aliens' home planet was a gas giant. If they were from an Earth-like planet, they wouldn't say that.

NEOWatcher
2014-Oct-08, 11:49 AM
Yellow star, Four planets, debris and 4 gas bubbles?

primummobile
2014-Oct-08, 12:49 PM
As I recall, the main impetus for the change was that other trans-Neptunian objects were discovered that were close to the same size as Pluto, and one that was even larger than Pluto. It made us realize that there are possibly many objects out there that could be called "planets" under the old definition.

If you think about it, Pluto is very strange when compared to the other planets. The eight planets all have orbits that are much more concentric, and they all orbit in the same plane. Pluto not only has a very elongated orbit compared to the planets, but it also crosses the orbit of a planet and it goes both above and below the plane of the solar system. Those three facts alone are enough for me to make a distinction between Pluto and the eight planets.

DonM435
2014-Oct-08, 12:59 PM
Also, Pluto "got smaller" every time they got a better measurement of it.

Remember, it was once a sizable-but-invisible Planet X affecting the orbits of Neptune and Uranus. When spotted, it was found to be small and dim. Along the way, a missed occultation caused estimates to be downsized. More lately, it's been found that part of its estimated diamater was really Charon.

Had they somehow known its true size back in 1930, I wonder if they'd have called it the Ninth Planet, or just considered it an asteroid (or two) on the loose?

redshifter
2014-Oct-10, 10:45 PM
I'm not sure why people call it a demotion anyway. It's a change in classification and that's it. We invented a term that better described what Pluto actually is and that's what we call it now.

This. Not sure why so many are so upset about Pluto's 'demotion'. There's nothing to be upset about IMO.

Hornblower
2014-Oct-11, 03:50 AM
Even before things came to a head at the 2006 IAU convention, there were planetary scientists saying that Pluto never would have been classified as a major planet if its small size had been recognized in 1930. If I am not mistaken, improved observations have shown that the reputed perturbations of Uranus, which were used by Lowell and Pickering to infer a large planet, were spurious.

DonM435
2014-Oct-11, 03:58 AM
I'm in agreement with the demotion. I just think that "dwarf planet" for a smaller non-planet is an incredibly stupid and clumsy designation.

rtroxel
2014-Oct-12, 12:07 PM
As I recall, the main impetus for the change was that other trans-Neptunian objects were discovered that were close to the same size as Pluto, and one that was even larger than Pluto. It made us realize that there are possibly many objects out there that could be called "planets" under the old definition.

If you think about it, Pluto is very strange when compared to the other planets. The eight planets all have orbits that are much more concentric, and they all orbit in the same plane. Pluto not only has a very elongated orbit compared to the planets, but it also crosses the orbit of a planet and it goes both above and below the plane of the solar system. Those three facts alone are enough for me to make a distinction between Pluto and the eight planets.

Here's a stray thought:

If Pluto's orbit goes within Neptune's orbit, then at that point, Pluto is no longer a trans-Neptunian object.

Roy

KaiYeves
2014-Oct-12, 02:46 PM
Here's a stray thought:

If Pluto's orbit goes within Neptune's orbit, then at that point, Pluto is no longer a trans-Neptunian object.

Roy

Well, "trans-" means "across", does it not?

primummobile
2014-Oct-12, 02:48 PM
Here's a stray thought:

If Pluto's orbit goes within Neptune's orbit, then at that point, Pluto is no longer a trans-Neptunian object.

Roy

A trans-neptunian object is something that crosses the orbit of Neptune.

rtroxel
2014-Oct-12, 04:15 PM
A trans-neptunian object is something that crosses the orbit of Neptune.

Yes, it does. I have been enlightened.:cool:

Roy

DonM435
2014-Oct-12, 06:32 PM
So what is the proper designation? That it's exo-Neptunian except for the relatively short period wherein it's intra-Neputnian? If it's the only one of the plutonian-class bodies that are occasionally closer than a legitmiate planet, maybe that does warrant special treatment.

primummobile
2014-Oct-12, 06:49 PM
So what is the proper designation? That it's exo-Neptunian except for the relatively short period wherein it's intra-Neputnian? If it's the only one of the plutonian-class bodies that are occasionally closer than a legitmiate planet, maybe that does warrant special treatment.

It's not. We don't know how many there are. But Eris may be larger than Pluto, also has a moon, and also crosses Neptune's orbit.

geonuc
2014-Oct-13, 09:14 AM
It's not. We don't know how many there are. But Eris may be larger than Pluto, also has a moon, and also crosses Neptune's orbit.

Are you sure Eris crosses Neptune's orbit? If so, the Wikipedia page needs to be corrected.

http://en.wikipedia.org/wiki/Eris_%28dwarf_planet%29#mediaviewer/File:Eris_Orbit.svg

Wikipedia also defines TNO somewhat differently that what has been stated here.

TNO Wiki page: http://en.wikipedia.org/wiki/Trans-Neptunian_object

any minor planet (http://en.wikipedia.org/wiki/Minor_planet) in the Solar System (http://en.wikipedia.org/wiki/Solar_System) that orbits (http://en.wikipedia.org/wiki/Orbit) the Sun (http://en.wikipedia.org/wiki/Sun) at a greater average distance (semi-major axis (http://en.wikipedia.org/wiki/Semi-major_axis)) than Neptune (http://en.wikipedia.org/wiki/Neptune).

Perhaps that also is incorrect, as that definition does not require the object to cross Neptune's path.

rtroxel
2014-Oct-13, 09:19 AM
Are you sure Eris crosses Neptune's orbit? If so, the Wikipedia page needs to be corrected.

http://en.wikipedia.org/wiki/Eris_%28dwarf_planet%29#mediaviewer/File:Eris_Orbit.svg

Wikipedia also defines TNO somewhat differently that what has been stated here.

TNO Wiki page: http://en.wikipedia.org/wiki/Trans-Neptunian_object


Perhaps that also is incorrect, as that definition does not require the object to cross Neptune's path.

It's been my understanding that there are many minor planets beyond Neptune's orbit. That's what I thought TNO meant.

Alas, now I'm confused again. :confused:

Roy

primummobile
2014-Oct-13, 09:28 AM
Are you sure Eris crosses Neptune's orbit? If so, the Wikipedia page needs to be corrected.

http://en.wikipedia.org/wiki/Eris_%28dwarf_planet%29#mediaviewer/File:Eris_Orbit.svg

Wikipedia also defines TNO somewhat differently that what has been stated here.

TNO Wiki page: http://en.wikipedia.org/wiki/Trans-Neptunian_object


Perhaps that also is incorrect, as that definition does not require the object to cross Neptune's path.

No, it looks like we are wrong.

As for Eris, I was intending to say it crosses Pluto's orbit. Don't post from a phone that only shows one line of text while watching a football game.

rtroxel
2014-Oct-13, 09:49 AM
No, it looks like we are wrong.

As for Eris, I was intending to say it crosses Pluto's orbit. Don't post from a phone that only shows one line of text while watching a football game.

...and, of course, if Eris and Pluto cross Neptune's orbit, does that mean that Neptune hasn't cleared its neighborhood??

Roy

Jens
2014-Oct-13, 10:01 AM
This. Not sure why so many are so upset about Pluto's 'demotion'. There's nothing to be upset about IMO.

I think there are two issues, both non-issues scientifically. One is that Pluto was the only planet discovered outside Europe, so there was a sense that the Europeans were picking on the US (though it's kind of a silly idea). And then, a slightly more understandable reason is that lots of textbooks and museum displays had to be rewritten. People were used to it.

Hornblower
2014-Oct-13, 11:45 AM
...and, of course, if Eris and Pluto cross Neptune's orbit, does that mean that Neptune hasn't cleared its neighborhood??

Roy
My bold. Once again, a misunderstanding of the IAU delegates' dumb-dumb choice of words. A better choice would have been "gravitationally dominates its neighborhood". There will never be a total absence of small stuff. Pluto and some other KBOs are locked in similar orbits in a 3:2 resonance with Neptune.

Hornblower
2014-Oct-13, 11:50 AM
It's been my understanding that there are many minor planets beyond Neptune's orbit. That's what I thought TNO meant.

Alas, now I'm confused again. :confused:

Roy

If the planetary scientists so wish, they could create subclassifications depending on whether or not the orbit of the body in question is eccentric enough to cross Neptune's orbital radius, as is done with Apollo and Amor for Earth-approaching asteroids.

swampyankee
2014-Oct-13, 01:11 PM
...and, of course, if Eris and Pluto cross Neptune's orbit, does that mean that Neptune hasn't cleared its neighborhood??

Roy


:-)

What does "clear its orbit" really, quantitatively, mean? 99%,95%, 90% of everything, or of objects over some cutoff mass? By number or by mass?

CJSF
2014-Oct-13, 06:20 PM
The "dwarf planet" classification really isn't very helpful, since it's only based on size (and that size's apparent effects). To name both Ceres and Pluto as dwarf planets ignores the likely vast compositional and developmental histories of the two and the objects in their corresponding regions of space. I don't begrudge Dr. Brown for capitalizing on Pluto's "death" at all and I think it's been a great help in getting the word out of what the outer solar system is like and how we're exploring it.

CJSF

danscope
2014-Oct-13, 07:42 PM
" Yeah, but they still killed Pluto. " (Sullen Pluto fan sulks in corner)

primummobile
2014-Oct-13, 08:02 PM
The "dwarf planet" classification really isn't very helpful, since it's only based on size (and that size's apparent effects). To name both Ceres and Pluto as dwarf planets ignores the likely vast compositional and developmental histories of the two and the objects in their corresponding regions of space. I don't begrudge Dr. Brown for capitalizing on Pluto's "death" at all and I think it's been a great help in getting the word out of what the outer solar system is like and how we're exploring it.

CJSF

But what about the vast compositional and size differences between planets? Certainly that's more than the differences between Pluto and Ceres. The diameter of Ceres is 40% that of Pluto and both are thought to have a rocky core surrounded by an icy mantle. Contrast that with the differences between Mars and Neptune.

CJSF
2014-Oct-13, 09:18 PM
But what about the vast compositional and size differences between planets? Certainly that's more than the differences between Pluto and Ceres. The diameter of Ceres is 40% that of Pluto and both are thought to have a rocky core surrounded by an icy mantle. Contrast that with the differences between Mars and Neptune.

I agree completely!

CJSF

Hornblower
2014-Oct-14, 01:50 AM
:-)

What does "clear its orbit" really, quantitatively, mean? 99%,95%, 90% of everything, or of objects over some cutoff mass? By number or by mass?I think it means that a small body that does not settle into a Trojan or resonant orbit will be either accreted or ejected within a period of time that is short compared with the age of the solar system. The orbital neighborhood will always have a small amount of transient junk in it. The continuing confusion over this "clearing" is a symptom of the poor job the IAU delegates did in communicating with the general public.

Hornblower
2014-Oct-14, 01:56 AM
I think there are two issues, both non-issues scientifically. One is that Pluto was the only planet discovered outside Europe, so there was a sense that the Europeans were picking on the US (though it's kind of a silly idea). And then, a slightly more understandable reason is that lots of textbooks and museum displays had to be rewritten. People were used to it.
Any educational institution worth a hill of beans should be able to supplement a lesson plan with bulletins about current or recent events pending the availability of new or revised textbooks.

Jens
2014-Oct-14, 10:12 AM
Any educational institution worth a hill of beans should be able to supplement a lesson plan with bulletins about current or recent events pending the availability of new or revised textbooks.

Well sure, I wasn't trying to justify it, just to explain where the opposition came from.

Amber Robot
2014-Oct-14, 05:43 PM
:-)

What does "clear its orbit" really, quantitatively, mean? 99%,95%, 90% of everything, or of objects over some cutoff mass? By number or by mass?

It goes something like this: (from burro.case.edu/Academics/Astr151/whatisaplanet.pdf)


A closely related criterion was
proposed by astronomer Michael
Brown of the California Institute of
Technology in 2004. He defined a planet
as “any body in the solar system that
is more massive than the total mass of
all of the other bodies in a similar orbit.”
To make this more precise, I have
suggested replacing “similar orbit”
with the concept of an orbital zone.
Two bodies share such a zone if their
orbits ever cross each other, if their orbital
periods differ by less than a factor
of 10, and if they are not in a stable resonance.

...

Earth, for example, shares its orbital
zone with an estimated 1,000 asteroids
larger than one kilometer in diameter,
most of which are relatively recent arrivals
from the main asteroid belt between
Mars and Jupiter. They add up to less
than 0.0001 percent of the mass of our
planet. The ratio between the mass of a
body and the mass of all other bodies
that share its orbital zone can be abbreviated
μ. For Earth, μ is about 1.7 million.
In fact, Earth appears to have the
highest μ value in the solar system. Jupiter
is 318 times more massive but shares
its orbital zone with a larger swarm of
bodies. Mars has the lowest μ value for
any of the planets (5,100), but even that
is far greater than the value for Ceres
(0.33) or Pluto (0.07) ...The result is striking: the
planets are in a different league from the
asteroids and KBOs, and Pluto is clearly
a KBO.

...

Such arguments persuaded the IAU
to define a planet in terms of “clearing”
its orbital neighborhood. The IAU may
need to amend the definition to specify
what degree of clearing qualifies a body
as a planet. I have suggested setting the
cutoff at a μ value of 100. That is, a body
in our solar system is a planet if it accounts
for more than 99 percent of the
mass in its orbital zone. But the exact
value of this cutoff is not critical. Any
value between about 10 and 1,000
would have the same effect.

Tom Mazanec
2014-Oct-19, 12:13 AM
The funny thing is I always disagreed with the status of Pluto.
When I was a student in the late 70s, I told my professor that it should not be a planet, because it was WAY smaller than any other planet, and because there was probably a spectrum of trans-Neptune objects ranging from comets to perhaps larger than Pluto. He flatly told me that it was a planet "by definition!"
When they downgraded it to Dwarf planet, I disagreed because the "clearing the orbit" criterion was just asking for a "Dwarf planet" larger than Earth, or at least larger than Mercury, which does not clear its orbit...in another planetary system if not in our own Solar System beyond Neptune.

grant hutchison
2014-Oct-24, 02:50 PM
Well, "trans-" means "across", does it not?I'm coming late to this. I see the meaning of transNeptunian has already been dealt with (it's the mean distance that lies beyond Neptune, not necessarily the whole orbit). The trouble is that trans- means "across" in two different ways: both "on the other side of" and "traversing". So we have "transalpine Gaul" (the bit of Gaul that lay on the other side of the Alps from Rome), and "transalpine railways" (which traverse the Alps). Chemistry uses trans- most frequently in the first sense (contrasting it with cis-, "on the same side of"); medicine uses it most frequently in the second sense.
It's confusing.

Grant Hutchison

swampyankee
2014-Oct-24, 03:19 PM
I think it means that a small body that does not settle into a Trojan or resonant orbit will be either accreted or ejected within a period of time that is short compared with the age of the solar system. The orbital neighborhood will always have a small amount of transient junk in it. The continuing confusion over this "clearing" is a symptom of the poor job the IAU delegates did in communicating with the general public.

That's one of the problems I see with the IAU definition -- the term "clear," at least as used in the IAU's press releases isn't very clear. The second, which is more conceptual is that I don't like a definition of "planet" vs "dwarf planet" that depends on location: if it's a planet in one part of the Solar System, then it should be one regardless of its location. Move Mercury to Pluto's orbit, and it probably becomes a dwarf planet. This is, to me, problematic. An archaean is an archaean where ever it's found; it doesn't become a bacterium because it's been moved. I don't have a problem with Pluto being a dwarf planet, per se: I have a problem with the criterion separating dwarf planet from planet.

(I don't tilt at windmills, so I'm not going to call Pluto a "planet." The people in charge of nomenclature have spoken.)

Hornblower
2014-Oct-28, 04:05 PM
That's one of the problems I see with the IAU definition -- the term "clear," at least as used in the IAU's press releases isn't very clear. The second, which is more conceptual is that I don't like a definition of "planet" vs "dwarf planet" that depends on location: if it's a planet in one part of the Solar System, then it should be one regardless of its location. Move Mercury to Pluto's orbit, and it probably becomes a dwarf planet. This is, to me, problematic. An archaean is an archaean where ever it's found; it doesn't become a bacterium because it's been moved. I don't have a problem with Pluto being a dwarf planet, per se: I have a problem with the criterion separating dwarf planet from planet.

(I don't tilt at windmills, so I'm not going to call Pluto a "planet." The people in charge of nomenclature have spoken.)
If the objective here is to make a general-public-friendly classification scheme, then I agree that it is a bit dicey to make something that is classified as a major planet in the inner solar system a dwarf if it is moved out to the Kuiper Belt. I have seen references that say Earth would be such a case, not massive enough to do what Neptune does out there. Nevertheless the scheme could be perfectly useful and OK for the needs of planetary scientists.

Quite frankly a reclassification of Pluto is perfectly analogous to the century earlier reclassification of Ceres et.al. I don't get the emotional reaction. Perhaps Walt Disney inadvertently contributed to it by coincidentally choosing the same name for Mickey's dog.

KaiYeves
2014-Oct-28, 09:11 PM
If the objective here is to make a general-public-friendly classification scheme, then I agree that it is a bit dicey to make something that is classified as a major planet in the inner solar system a dwarf if it is moved out to the Kuiper Belt. I have seen references that say Earth would be such a case, not massive enough to do what Neptune does out there. Nevertheless the scheme could be perfectly useful and OK for the needs of planetary scientists.

Quite frankly a reclassification of Pluto is perfectly analogous to the century earlier reclassification of Ceres et.al. I don't get the emotional reaction. Perhaps Walt Disney inadvertently contributed to it by coincidentally choosing the same name for Mickey's dog.
It may not have been coincidental-- the dog got his current name several months after the dwarf planet, but there apparently aren't any documents in the Disney archives making it definite that the dog was named for the planet.

rtroxel
2014-Nov-02, 03:15 PM
Here's an interesting Facebook page on the subject of Pluto:

https://www.facebook.com/groups/398034826873967/

NEOWatcher
2014-Nov-03, 12:52 PM
... And for those of us not on Facebook?

rtroxel
2014-Nov-03, 01:00 PM
The full name of the group is The Society of Unapologetic Pluto Huggers. They don't have a web site, but this is how they define their FB group:

"A group for Pluto huggers and those who think the current IAU definition of a planet is too restrictive and needs to be adjusted in a reasonable, scientific way that makes more sense, enabling dwarf planets to be considered as much a planet as Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and nefarious Neptune! Just kidding, Neptune! For a gas giant, you rock, dude!"

HowlerMonkey
2014-Nov-03, 02:11 PM
I have developed my own classification system, which I propose here.

Any small (less than 3,000 km radius) rocky planet with a very thin atmosphere and an orbit entirely within 100 million of the sun, will be called a "Mercury."

Any medium-sized (between 3,000 km and 10,000 km radius) rocky planet with a very thick atmosphere and an orbital period of less than 8,000 hours will be called a "Venus."

Any medium-sized rocky planet with a modest atmosphere, large pools of surface liquid, and orbital period between 8,000 and 10,000 hours will be called an "Earth."

Any medium-sized rocky planet with a very thin atmosphere and more than one natural satellite, and an orbital period of less than 20,000 hours will be called a "Mars."

Any large (greater than 10,000 km radius) gaseous planet with prominent red spot(s), which was known to ancient astronomers, will be called a "Jupiter."

Any large gaseous planet with prominent rings visible with the aid of 17th-century quality telescopes, will be called a "Saturn."

Any large gaseous planet, first identified as a planet during the 18th century, will be called a "Uranus."

Any large gaseous planet, first identified as a planet during the 19th century, will be called a "Neptune."

Any small rocky planet, first identified as a planet during the first half of the 20th century, with a highly elliptical orbit, will be called a "Pluto."

I call upon all board members to rally to the support of this unique, innovative, and improved classification system.

Swift
2014-Nov-03, 02:38 PM
Hi HowlerMonkey, welcome to CQ.


<snip>
Any medium-sized rocky planet with a modest atmosphere, large pools of surface liquid, and orbital period between 8,000 and 10,000 hours will be called an "Earth."


So, you propose naming a planet "dirt"? ;)

A little more seriously - your system won't work for the vast majority of large gaseous planets in the Universe, since they were not identified in the 17th, 18th, or 19th centuries.

HowlerMonkey
2014-Nov-03, 03:10 PM
So, you propose naming a planet "dirt"? ;)

It's better than being called "Uranus"!


A little more seriously - your system won't work for the vast majority of large gaseous planets in the Universe, since they were not identified in the 17th, 18th, or 19th centuries.

Those do not fit into the categories enumerated above. But the system is flexible, and can be expanded to include additional categories for objects which don't fit into the older categories.

publiusr
2014-Nov-03, 08:33 PM
If having more than nine planets gets kids more interested in space--then I'm all for it.

Barabino
2014-Dec-04, 12:34 PM
Probably the point is not 9 or 10 planets, but that gas giants and ice giants don't really count in as planets, because you can't possibly land on them and shoot photos of the surface :-/

They refuse to be "a place"...

Gorn
2015-Jul-19, 02:37 PM
Hello. I would just like to remark how much I like the pictures I have seen of Pluto..and Charon. I get the crazy 'sense' of Pluto..being the 'planet'..and Charon..being its moon...

Does anyone else get that?....

I think it is a bit of 'luck' for the new horizons team etc, etc.

Bye
G

swampyankee
2015-Jul-19, 02:47 PM
"Trans" is being used to mean "beyond," although it can also be used to mean "across" (trans-continental). Perhaps extra-, supra-, or para-Neptunian would be better ;)

NEOWatcher
2015-Jul-19, 10:22 PM
"Trans" is being used to mean "beyond," although it can also be used to mean "across" (trans-continental).
It does go "beyond" Neptune, it also goes "across" Neptune's orbital distance. ;)

KaiYeves
2015-Jul-19, 11:24 PM
Hello. I would just like to remark how much I like the pictures I have seen of Pluto..and Charon. I get the crazy 'sense' of Pluto..being the 'planet'..and Charon..being its moon...

Does anyone else get that?....

I think it is a bit of 'luck' for the new horizons team etc, etc.

Bye
G

There's nothing crazy about it-- Charon is a satellite of Pluto, although technically they both orbit a mutual center of gravity outside of Pluto's surface.

CJSF
2015-Jul-20, 01:34 PM
There's nothing crazy about it-- Charon is a satellite of Pluto, although technically they both orbit a mutual center of gravity outside of Pluto's surface.

With the barycenter outside of both bodies, there's nothing but convention to say that Pluto isn't a satellite of Charon though, right?

CJSF

KaiYeves
2015-Jul-20, 01:48 PM
With the barycenter outside of both bodies, there's nothing but convention to say that Pluto isn't a satellite of Charon though, right?

CJSF
I guess. That's why they're sometimes called a "double system".

Jens
2015-Jul-20, 01:50 PM
That's right. In most cases it's very clear which is the satellite, but in the case of Pluto and Charon, it's a bit more ambiguous. But still, Pluto is the bigger of the two.

Grey
2015-Jul-20, 03:28 PM
But still, Pluto is the bigger of the two.And pretty significantly so, just about twice the radius and nine times the mass.

demeter
2015-Jul-20, 05:41 PM
Pluto should not allow itself to be reinstated on the old terms. It should demand a pay rise and a better orbit.

swampyankee
2015-Jul-20, 05:54 PM
With the barycenter outside of both bodies, there's nothing but convention to say that Pluto isn't a satellite of Charon though, right?

CJSF


Well, Pluto is more massive than Charon, and it is convention to say that the primary is more massive than any single satellite. It's also a formal convention that says that Pluto is a dwarf planet.

CJSF
2015-Jul-22, 02:20 PM
Well, Pluto is more massive than Charon, and it is convention to say that the primary is more massive than any single satellite.
Yes, that's what I said. Convention.

CJSF

malaidas
2015-Jul-23, 07:51 AM
Pluto should not allow itself to be reinstated on the old terms. It should demand a pay rise and a better orbit.

Lol. There is no way the major planets will let it back in the group,it couldn't keep a tidy workspace, kept getting in Neptunes way and was too 'far out' most of the time.

thoth II
2015-Oct-07, 07:40 PM
Pluto has all the qualities of a planet, but it really should be reclassified as a Kuiper belt object.

KaiYeves
2015-Oct-07, 08:39 PM
Pluto has all the qualities of a planet, but it really should be reclassified as a Kuiper belt object.

Well, it's a Kuiper dwarf, right? Just like Ceres is an asteroid dwarf. Both are members of those classes of minor body that are also large and round enough to be dwarf planets.

Amber Robot
2015-Oct-07, 10:53 PM
Pluto has all the qualities of a planet, but it really should be reclassified as a Kuiper belt object.

The problem with Pluto is that not everyone seems to agree on what the formal qualities of a "planet" should be. I really see no problem in it having double designation: a planet and a KBO. What is the formal definition of a KBO?

thoth II
2015-Oct-14, 05:41 PM
The Kuiper Belt objects are a series of minor objects existing beyond the orbit of Neptune and out to about 50 AU . Pluto and Makemake could be considered Planets except for the IAU condition that they clear their orbits of other objects. So yes, they could be planets. I think that they shouldn't be planets simply because I'd like to have them on the same footing as the rest of the KBOs: they have a similar history of formation and composition.

Amber Robot
2015-Oct-14, 05:51 PM
I'd like to have them on the same footing as the rest of the KBOs: they have a similar history of formation and composition.

I'll wait until planetary scientist have had some time to fully analyze all the great New Horizons data of Pluto before assuming that we fully understand the history of formation and composition of Pluto and other KBOs.

thoth II
2015-Oct-14, 08:22 PM
"I'll wait until planetary scientist have had some time to fully analyze all the great New Horizons data of Pluto before assuming that we fully understand the history of formation and composition of Pluto and other KBOs. "

you are absolutely correct. They have a lot to learn still about Pluto and other KBOs. I just have an educated guess that they are all similar because they share similar orbits and probably were formed at the same time in history from the same cause, probably condensation in a very diffuse solar nebula cloud in that region.

swampyankee
2015-Oct-14, 11:01 PM
KBO is something in the Kuiper Belt, so I would think just about anything short of a brown dwarf (and maybe even that) could be one.

This brings up a new question for the IAU: how is the Kuiper Belt defined? Where does it start and end? Does a binary system have multiple analogies to the Kuiper Belt?

roxanwright
2016-Jun-30, 05:27 AM
I don't think so. According to some sources I read online Pluto will not be reinstated as a planet and will continue to be known as a dwarf planet.

Solfe
2016-Jul-01, 05:07 AM
"Don't cry Pluto, I'm not a planet either..." My son's favorite T-shirt when he was 3-4.

Solfe
2016-Jul-01, 05:13 AM
Do you think there is some subset of IAU members that spice up papers about Pluto by reading them like Samuel L. Jackson would?

"Oh, it another paper about the dwarf planet, Pluto."
"PlooTow! <mumble... mumble... cuss words> Always PlooTow!"

BigDon
2016-Aug-09, 07:14 PM
And a recently spied tee shirt states;

"Dear NASA, your mom thought I was big enough.

Sincerely Pluto."

Yikes, serious burn from Pluto there NASA.

thoth II
2017-Jan-23, 07:33 PM
there are too many KBOs similar to Pluto to recognize Pluto as a planet. What, is IAU going to name all these KBOs planets also?

spare part
2017-Jan-23, 11:26 PM
We could just reclassify all the planets as dwarf planets.

Roger E. Moore
2017-Jan-28, 03:40 AM
there are too many KBOs similar to Pluto to recognize Pluto as a planet. What, is IAU going to name all these KBOs planets also?

Plutinos.

swampyankee
2017-Jan-28, 02:39 PM
there are too many KBOs similar to Pluto to recognize Pluto as a planet. What, is IAU going to name all these KBOs planets also?

The categories "planet" and "dwarf planet" have been defined; it shouldn't matter if there are two members in a class or 2000. Biologists have several genera with over a thousand species, e.g., http://www.fond4beetles.com/Buprestidae/WorldCat/Genera/Agrilus.htm; objecting to a category because it's got too many members won't be looked at with much sympathy.

CJSF
2017-Jan-29, 03:02 AM
One (but not the only) issue I have with the notion of "dwarf planet" in the context of our solar system is that it categorizes two broadly different object populations as the same. I get that one can do that, but I don't think it serves the astronomy community or the interested public to leave the formation and evolutionary history out of the categorization of these objects. Or maybe not leaving it out, but it is irrelevant if you already have categories like "plutino" or whatever. But as an interested layman, I don't lose sleep over it.

CJSF

swampyankee
2017-Jan-29, 03:28 AM
One (but not the only) issue I have with the notion of "dwarf planet" in the context of our solar system is that it categorizes two broadly different object populations as the same. I get that one can do that, but I don't think it serves the astronomy community or the interested public to leave the formation and evolutionary history out of the categorization of these objects. Or maybe not leaving it out, but it is irrelevant if you already have categories like "plutino" or whatever. But as an interested layman, I don't lose sleep over it.

CJSF

While I happen to think the "dwarf planet" category is badly defined, and its rational worse explained, it is what the IAU decided to use. Until they come up with a better system, which should take a short period of thought followed by about ten years of discussion, they're stuck with it.

dtilque
2017-Feb-08, 12:41 AM
One (but not the only) issue I have with the notion of "dwarf planet" in the context of our solar system is that it categorizes two broadly different object populations as the same.

You sure you didn't mean "planet" there? That sentence applies even more to planets than dwarf planets.

Personally, they should just get rid of the category "dwarf planet" altogether. It serves absolutely no scientific purpose or even bureaucratic purpose, which is probably why they haven't added any new ones since the original 5.

Roger E. Moore
2017-Feb-22, 01:27 AM
Pluto, Ganymede, and the MOON will be PLANETS??? WTF

http://www.popsci.com/pluto-might-be-planet-again

http://www.astronomy.com/news/2017/02/will-pluto-be-a-planet-again

http://gizmodo.com/nasa-scientists-have-a-plan-to-make-pluto-a-planet-agai-1792554863

http://www.popularmechanics.com/space/solar-system/news/a25327/pluto-planethood-plan/

Roger E. Moore
2017-Feb-22, 02:50 AM
[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
2017-Feb-22, 03:11 AM
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? (http://www.universetoday.com/133525/sad-pluto-110-planets-solar-system-instead/)


Their study Ė titled ďA Geophysical Planet Definitionď, which was recently made available on the Universities Space Research Association (USRA) website Ė addresses what the team sees as a need for a new definition that takes into account a planetís 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 donít need the IAU definition.

Roger E. Moore
2017-Feb-22, 04:06 AM
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
2017-Feb-22, 07:08 AM
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
2017-Feb-22, 07:13 PM
NASA is now officially on board with the movement to designate Pluto a full-fledged planet again:


http://www.usatoday.com/story/tech/nation-now/2017/02/21/pluto-have-last-laugh-nasa-scientists-wants-make-pluto-planet-again/98187922/

Amber Robot
2017-Feb-22, 08:35 PM
NASA is now officially on board with the movement to designate Pluto a full-fledged planet again:


http://www.usatoday.com/story/tech/nation-now/2017/02/21/pluto-have-last-laugh-nasa-scientists-wants-make-pluto-planet-again/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
2017-Feb-23, 03:17 AM
NASA is now officially on board with the movement to designate Pluto a full-fledged planet again:

http://www.usatoday.com/story/tech/nation-now/2017/02/21/pluto-have-last-laugh-nasa-scientists-wants-make-pluto-planet-again/98187922/

And USA Today is just regurgitating the Gizmodo article: NASA Scientists Have a Plan to Make Pluto a Planet Again (http://gizmodo.com/nasa-scientists-have-a-plan-to-make-pluto-a-planet-agai-1792554863), 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 (http://www.hou.usra.edu/meetings/lpsc2017/) 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
2017-Feb-23, 01:10 PM
For some reason this argument reminds me of the time we had a sixth Great Lake.

http://www.nytimes.com/1998/03/07/us/champlain-becomes-the-sixth-great-lake.html

danscope
2017-Feb-23, 03:48 PM
Why it's the biggest little lake we've got !!! :)

DonM435
2017-Feb-23, 03:52 PM
Attempted embiggening, I'd say.

Roger E. Moore
2017-Feb-23, 04:35 PM
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
2017-Feb-25, 08:02 PM
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
2017-Feb-26, 05:58 AM
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 (http://www.blastr.com/2017-2-21/redefining-planets-answer-search-question)


And therein lies my basic problem with all this. Iím OK with this new idea, but not if itís called a definition! That may seem like semantics, but itís 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 ďgreenĒ. And when you get near the borders, things get fuzzy, indeed.

Canis Lupus
2017-Mar-30, 10:45 PM
And therein lies my basic problem with all this. Iím OK with this new idea, but not if itís called a definition! That may seem like semantics, but itís 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 ďgreenĒ. 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
2017-Mar-31, 12:39 AM
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
2017-Apr-01, 10:08 PM
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
2017-Apr-12, 06:12 PM
The IAU's decision: Pluto and the Solar System | IAU (https://www.iau.org/public/themes/pluto/)


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


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 (http://www.planetary.org/multimedia/space-images/charts/every-round-object-under-10k-2015.html): Mars, Ganymede, Titan, Mercury, Callisto, ...

lpetrich
2017-Apr-12, 06:30 PM
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
2017-Apr-13, 12:15 AM
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
2017-Apr-13, 12:33 AM
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
2017-Apr-13, 01:33 AM
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
2017-Apr-13, 01:47 AM
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 https://www.nature.com/article-assets/npg/srep/2016/161123/srep37740/images/srep37740-m1.gif + 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 https://www.nature.com/article-assets/npg/srep/2016/161123/srep37740/images/srep37740-m2.gif 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
2017-Apr-13, 02:28 AM
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
2017-Apr-13, 03:54 AM
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
2017-May-03, 07:32 PM
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
2017-May-05, 06:47 PM
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
2017-May-05, 06:52 PM
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
2017-May-05, 07:14 PM
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
2017-May-05, 07:22 PM
Comets? Asteroids?

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

Swift
2017-May-05, 08:13 PM
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.

swampyankee
2017-May-05, 10:49 PM
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.

My goal is to have a sensible taxonomic classification. The IAU's isn't, as a) it's explicitly limited to the Solar System and b) identical objects would change categories based on location. Pick a mass or a property. Hydrostatic equilibrium, composition, combination of the two all make sense.

Any classification should be based solely on the body's intrinsic properties.

Swift
2017-May-06, 12:36 AM
My goal is to have a sensible taxonomic classification. The IAU's isn't, as a) it's explicitly limited to the Solar System and b) identical objects would change categories based on location. Pick a mass or a property. Hydrostatic equilibrium, composition, combination of the two all make sense.

Any classification should be based solely on the body's intrinsic properties.
So, is a moon of Jupiter, if it fit this set of properties, a planet?

swampyankee
2017-May-06, 11:07 AM
So, is a moon of Jupiter, if it fit this set of properties, a planet?

If it would be if it directly orbits a star, certainly.

Swift
2017-May-06, 01:49 PM
If it would be if it directly orbits a star, certainly.
But isn't that "b) identical objects would change categories based on location"?

My goal is to have a sensible taxonomic classification. The IAU's isn't, as a) it's explicitly limited to the Solar System and b) identical objects would change categories based on location. Pick a mass or a property. Hydrostatic equilibrium, composition, combination of the two all make sense.


Titan, for example, is a planet if it orbits the sun, but a moon if it orbits Saturn?

Again, I'm fine with the classification changing depends on what it orbits (and the nature of that orbit), but I didn't think you were.

swampyankee
2017-May-06, 02:48 PM
But isn't that "b) identical objects would change categories based on location"?
Titan, for example, is a planet if it orbits the sun, but a moon if it orbits Saturn?

Again, I'm fine with the classification changing depends on what it orbits (and the nature of that orbit), but I didn't think you were.


I can't communicate clearly on my tablet ;)

If something meets some definition of "planet," based on its intrinsic properties when it's orbiting a star (not just the Sun, but any star), it would remain a planet if it orbits a planet or if it's wandering in intergalactic space orbiting nothing.

agingjb
2017-May-07, 07:18 AM
I can't communicate clearly on my tablet ;)

If something meets some definition of "planet," based on its intrinsic properties when it's orbiting a star (not just the Sun, but any star), it would remain a planet if it orbits a planet or if it's wandering in intergalactic space orbiting nothing.

It certainly should do. The fact that there are definitions of "planet" that rule out candidates based on what they orbit does, in my opinion, make "planet" a useless term in any scientifically appropriate taxonomy of objects in space.

First mass, second composition, third surface characteristics, orbit irrelevant, would be my ordering.

Canis Lupus
2017-Jun-11, 07:41 AM
But isn't that "b) identical objects would change categories based on location"?


Titan, for example, is a planet if it orbits the sun, but a moon if it orbits Saturn?

Again, I'm fine with the classification changing depends on what it orbits (and the nature of that orbit), but I didn't think you were.

Can't see the problem of an object being both. Moon refers to a reference point of orbit, whereas planet to intrinsic characteristics regardless of position.

Sardonicone
2017-Jul-01, 12:14 AM
Would either Titan or Ganymede "clear their orbits" had they been thrust into interplanetary space? I'm asking because I genuinely don't know.

swampyankee
2017-Jul-01, 03:16 PM
Would either Titan or Ganymede "clear their orbits" had they been thrust into interplanetary space? I'm asking because I genuinely don't know.

It would depend on where you put them in orbit around the Sun. Right now, were any of the terrestrial planets moved sufficiently far from the Sun, they would fail the "clear its orbit" requirement, and change category. If not bound to the Sun, they would fail the "bound directly to the Sun" requirement.

Sardonicone
2017-Jul-01, 03:41 PM
It would depend on where you put them in orbit around the Sun. Right now, were any of the terrestrial planets moved sufficiently far from the Sun, they would fail the "clear its orbit" requirement, and change category. If not bound to the Sun, they would fail the "bound directly to the Sun" requirement.

I was thinking more along the lines of them being part of the inner solar system. Not that our system is any standard bearer for how they are set up across the cosmos.

swampyankee
2017-Jul-01, 05:07 PM
I was thinking more along the lines of them being part of the inner solar system. Not that our system is any standard bearer for how they are set up across the cosmos.

Somewhere or another on Cosmoquest, there's a link to a site which calculates a value based on a formula developed by Margot which will tell whether or not an object will clear its orbit. I suspect that either Ganymede or Titan, in direct orbit about the Sun, would satisfy the "clearing orbit" criterion out to a few AU.

Hypmotoad
2017-Jul-20, 06:37 AM
Here's the thing, we all or most of us grew up 'knowing' Pluto is a planet. We humans like things orderly and Pluto should be a planet simply because it was discovered and counted as one for years. To say Pluto cannot be a planet because of it's size is like saying Israel cannot be a nuclear power because of it's size.

We mostly humans love 9nth planets that begin with the letter P. Sorry, but is true. And there is supposedly new evidence of a '9th planet' massing 10x earth.

I sense renewal of 'Ancient Aliens' for 3 more seasons.

Swift
2017-Jul-20, 12:45 PM
To say Pluto cannot be a planet because of it's size is like saying Israel cannot be a nuclear power because of it's size.

That analogy makes no sense to me.

The nature of science is that we change as we get new information. Classifying animals by species constantly changes as new information comes along - look up how many times Northern Orioles and Baltimore Orioles went back and forth (LINK (http://www.learner.org/jnorth/tm/oriole/Baltimore-BullocksSplit_Rising.html)). Should we decide the validity of science by the criteria "well, that's not what it was when I grew up"?

Sure, let's debate about what definitions of planets are valid, useful, and are supported by the data. But setting it because someone memorized "My Very Elegant Mother Just Sat Upon Nine Pins" is silly.

Tom Mazanec
2017-Aug-16, 09:30 PM
Isn't this sort of like arguing whether a certain bit of rock is the world's biggest grain of sand or the world's smallest gravel granule?
Anyway, I would vote "planet". Just my three cents (inflation don't you know).

swampyankee
2017-Aug-17, 03:00 AM
Isn't this sort of like arguing whether a certain bit of rock is the world's biggest grain of sand or the world's smallest gravel granule?
Anyway, I would vote "planet". Just my three cents (inflation don't you know).

There are explicit definitions which define gravel vs sand vs silt in civil engineering and geology. Interestingly, the ASTM definition doesn't change if the gravel is in California or Florida.

Weltraum
2017-Nov-17, 04:07 AM
What really seems out of date is the old classification system. We now have to add gas dwarfs* (http://www.fromquarkstoquasars.com/meet-the-newest-classification-for-planets-the-gas-dwarf/), apparently.

* Spelling rules for dwarfs/dwarves (http://grammarist.com/usage/dwarfs-dwarves/).

It's unfortunate how many typographical errors that article has. Cool info, though. I like that we have apparently already discovered a class of planet that does not even exist in our solar system. Well, I guess there are at least two or three, given the prevalence of "hot Jupiters" and "super Earths" out there as well.

FrankWSchmidt
2017-Nov-21, 12:20 AM
I think the classification of solar system objects is OK when it has only 8 planets, and as for recognizing them, I prefer Margot's approach (and I don't like Soter's - if Planet 9 is found, we could never use Soter to check it, since we cannot see most of the minor objects that might be crossing its orbit).

It's the rest of the classification I find odd - we have 5 dwarf planets, then an ever-growing triple-digit number of moons most of which are tiny, then about a million small objects.

And while the 8 planets are divided into subtypes - 4 terrestrials, 2 gas giants, and 2 ice giants - almost all of the subdivisions of the small objects are just by where they orbit and not what they are (the exception being the division between asteroids and comets).

Personally, I'd like another classification:
On the top, there'd still be the 8 planets (recognized by Margot's equation).
The remaining objects, including moons, are first divided up into planetoids and small objects. I personally would draw the line by mass, and would choose 2.5 * 10^19 kg as the minimum mass for planetoids. Then all of the very round objects would be planetoids including Mimas, while all of the rubble piles up to 87 Sylvia would be among the small objects.
I think among the satellites, only those who are planetoids should be called moons. That would mean Jupiter would have only 4 moons - but the 5th most massive of Jupiter's satellites, Himalia, already has less mass than the most massive Trojan, Hektor.

Then I think the planetoids should have subtypes regarding mass and composition (the least massive ones would still be monolithic objects and not rubble pile, but they wouldn't be round, etc). I think the planets would qualify as planetoids as well, but there'd be little overlap - there would be no gas giant that wouldn't qualify as planet, and no irregular planetoid that would.

Is there any serious proposal inside the scientific community or IAU that's at least a little similar to this?

Swift
2017-Nov-21, 09:00 PM
I've moved this thread from Citizen Science - Exploring the Kuiper Belt, where it never really belonged. The Citizen Science sub-fora are for discussing the citizen science projects, particularly ones supported by CQ,
not general science or astronomy discussions.

Jeff Root
2017-Nov-22, 10:44 PM
I haven't posted in this thread before, so I'll do it now.

Back in 2003 I put up a web page with a simple one-dimensional
graph of moon diameters. It shows how the sizes of moons happen
to fall into five clusters. I lumped together some of the clusters in
order to fit them all into three arbitrary groups that I labelled "large",
"medium", and "small". In addition to the 28 largest moons, I show
the two smallest planets (Mercury and Pluto) and the two largest
asteroids known in 2003 (Ceres and Pallas):

http://www.freemars.org/jeff2/moons1a.htm

You can see that the biggest gap in absolute value is within the
group of "large" moons: Between Io at 3630 km and Callisto at
4800 km there were no known objects. That gap is in the middle
of the group of what I called "large" moons.

The next-biggest gap is between Titania at 1578 km and Pluto at
2275 km diameter. Pluto falls in the gap between the "large" moons
and the "medium" moons. Leaving out Pluto, that gap is almost as
big in absolute terms as the gap between Io and Callisto, and is
larger in relative terms.

The point I want to make from this graph is that Pluto is way, way
bigger in relative terms than the largest asteroid then known, Ceres,
and way bigger than moons in the "medium" group. It happens to
be roughly halfway between the otherwise-smallest known planet
(Mercury) and the otherwise-largest then-known asteroid (Ceres).

-- Jeff, in Minneapolis

Eclogite
2017-Nov-23, 12:44 PM
Asteroids, planets, comets, sednoids, moons, plutinos, ice giants, Kuiper Belt Objects, super Earths, satellites, dwarf planets, plutoids, hot Jupiters, trojans, gas giants, Trans Neptunian Objects, centaurs, minor planets, scattered disc objects, cubewanos, and terrestrial planets. Did I miss anything?

The point has likely been made already, but is worth repeating: classification systems are:

Artificial
Created for convenience
Subject to change over time
Not created for the satisfaction of the general public



Fortunately, the vast majority of scientists, for the vast majority of time, do not get wrapped up in ultimately incidental nuances, but focus instead of investigating the nature of these bodies, regardless of what they are called.

What's in a name? that which we call a rose
By any other word would smell as sweet;

William Shakespeare - Romeo and Juliet Act II, Scene 2

FrankWSchmidt
2017-Nov-23, 03:36 PM
Asteroids, planets, comets, sednoids, moons, plutinos, ice giants, Kuiper Belt Objects, super Earths, satellites, dwarf planets, plutoids, hot Jupiters, trojans, gas giants, Trans Neptunian Objects, centaurs, minor planets, scattered disc objects, cubewanos, and terrestrial planets. Did I miss anything?

The point has likely been made already, but is worth repeating: classification systems are:

Artificial
Created for convenience
Subject to change over time
Not created for the satisfaction of the general public



Fortunately, the vast majority of scientists, for the vast majority of time, do not get wrapped up in ultimately incidental nuances, but focus instead of investigating the nature of these bodies, regardless of what they are called.

What's in a name? that which we call a rose
By any other word would smell as sweet;

William Shakespeare - Romeo and Juliet Act II, Scene 2

The Solar System has 8 planets, further subdivided into 4 terrestrial planets, 2 gas giants, 2 ice giants, no super Earths and no hot Jupiters. It also has 5 dwarf planets, further subdivided into 4 plutoids and Ceres.

All other objects are just broadly categorised as being either satellites/moons, asteroids/minor planets or comets, while the rest of categories you name are about where those objects are, not what they are.

So if we want to know what they are, we have extreme subdivisions for 13 objects and barely any for the rest. While the thread name is about Pluto, I think it's already part of a small elite - all those beyond the top 13 are lumped together into groups filled mostly with tiny objects that nobody would be interested to know anything about.

grapes
2018-Sep-12, 09:41 AM
From my twitter


Pluto a Planet? New Research from UCF Suggests Yes https://today.ucf.edu/pluto-planet-research/

Alan Stern is a co-author of course.

selden
2018-Sep-12, 11:01 AM
My understanding is that Pluto actually lost its classification as a planet because it was discovered to be just one of a large number of similar objects residing in the region of the Solar System called the Kuiper Belt. My impression is that the revised definition of "planet" was an attempt to have a definition which is compatible with that discovery.

George
2018-Sep-12, 05:07 PM
My understanding is that Pluto actually lost its classification as a planet because it was discovered to be just one of a large number of similar objects residing in the region of the Solar System called the Kuiper Belt. My impression is that the revised definition of "planet" was an attempt to have a definition which is compatible with that discovery.That's my recollection as well, but, IIRC, Mike Brown had discovered Eris (2005) and there was a chance it would be found to be larger than Pluto, which added drama to this story. The IAU vote came not long after the renaming of this KBO to "Eris".