From the “Make Pluto Great Again” department, new definition raises number of planets in solar system to about 110
Johns Hopkins University scientist Kirby Runyon wants to make one thing clear: Regardless of what one prestigious scientific organization says to the contrary, Pluto is a planet.
So, he says, is Europa, commonly known as a moon of Jupiter, and so is the Earth’s moon, and so are more than 100 other celestial bodies in our solar system that are denied this status under the prevailing definition of “planet.”
The definition approved by the International Astronomical Union in 2006 demoted Pluto to “non-planet,” thus dropping the consensus number of planets in our solar system from nine to eight. The change – a subject of much scientific debate at the time and since – made no sense, says Runyon, lead author of a short paper making the pro-Pluto argument that will be presented next week at a scientific conference in Texas.
Icy, rocky Pluto had been the smallest of the nine planets, its diameter under three-quarters that of the moon and nearly a fifth of Earth. Still, says, Runyon, who is finishing his doctorate this spring in the Department of Earth and Planetary Sciences, Pluto “has everything going on on its surface that you associate with a planet. … There’s nothing non-planet about it.”
Runyon, whose doctoral dissertation focuses on changing landscapes on the moon and Mars, led a group of six authors from five institutions in drafting a proposed new definition of “planet,” and a justification for that definition. Both will be presented at the Lunar and Planetary Science Conference’s poster session. The poster will be on view for a full day on March 21 at the conference sponsored by the Lunar and Planetary Institute, and Runyon will be on hand for at least three hours to answer questions about it.
The other authors are S. Alan Stern and Kelsi Singer of the Southwest Research Institute in Boulder, Colorado; Tod Lauer of the National Optical Astronomy Observatory in Tucson, Arizona; Will Grundy of the Lowell Observatory in Flagstaff, Arizona; Michael Summers of George Mason University in Fairfax, Virginia. All the authors are science team members on the New Horizons mission to Pluto, operated for NASA by the Johns Hopkins University Applied Physics Laboratory. In the summer of 2015, the New Horizons spacecraft became the first to fly by Pluto, some 4.67 billion miles from Earth, passing within 8,000 miles and sending back the first close-up images ever made of Pluto.
Runyon and his co-authors argue for a definition of “planet” that focuses on the intrinsic qualities of the body itself, rather than external factors such as its orbit or other objects around it. They define a planet as “a sub-stellar mass body that has never undergone nuclear fusion” and that has enough gravitational heft to maintain a roughly round shape. (Even if it bulges at the equator because of a three-way squeeze of forces created by its own gravity and the influence of both a star and a nearby larger planet.)
This definition differs from the three-element IAU definition in that it makes no reference to the celestial body’s surroundings. That portion of IAU’s 2006 formula – which required that a planet and its satellites move alone through their orbit – excluded Pluto. Otherwise, Pluto fit the IAU definition: It orbits the sun and it is massive enough that the forces of gravity have made it round.
Stern, the principal investigator for the New Horizons mission, has argued in the past that the IAU definition also excludes Earth, Mars, Jupiter and Neptune, which share their orbits with asteroids.
The proposed new geophysical definition omits stars, black holes, asteroids and meteorites, but includes much of everything else in our solar system. It would expand the number of planets from eight to approximately 110.
That expansion is part of the appeal of the new definition, Runyon says. He says he would like to see the public more engaged in solar system exploration. As the very word “planet” seems to carry a “psychological weight,” he figures that more planets could encourage that public interest.
The new definition, which does not require approval from a central governing body, is also more useful to planetary scientists. Most of them are closely affiliated with geology and other geosciences, thus making the new geophysical definition more useful than the IAU’s astronomical definition.
He has some reason to be optimistic, as the new definition has already been adopted by Planet Science Research Discoveries, an educational website founded by scientists at the University of Hawaii at Mānoa.
“I want the public to fall in love with planetary exploration as I have,” Runyon said. “It drives home the point of continued exploration.”
###
Source: JOHNS HOPKINS UNIVERSITY
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As I recollect the demotion of Pluto was rather a dodgy stitch up late on the Friday pm session of the IAU when the proponents of the change knew most of the delegates would be on their way to catch flights home – it is questionable if their motion would have succeeded otherwise. And several people have commented rightly that on the grounds they stated for the exclusion of Pluto other planets too should therefore be disqualified. JBom correctly points out the interwoven orbits of the Earth and Moon.
But more than that this silly exclusion of Pluto caused a lot of unnecessary disappointment to lots of young people interested in Astronomy for virtually no real gain. So what if professional astronomers have to grapple with complex definitions of small planets and minor bodies? The public didn’t need to be involved unless they took a deeper interest.
In any case the demotion merely looked what it was – a churlish act – once we discovered how interesting and active Pluto actually is.
There is real gain, since without the dwarf planet status, more and more tiny “planets” will be discovered in the outer reaches of the solar system. IMO the IAU did the right thing.
Anything that pops Neil Degrasse Tyson;s bubble I’m in favor of.
The Kardashian sister of PBS science like programming. Social Justice demanded the invention of.
So the “gain” is we don’t have to acknowledge a potential host of minor planets which in fact tell us the solar system is much more extensive than once realised. I think professional astronomers are robust enough to cope with that without messing about with the status of Pluto (whatever reservations they might have about it) . No gain, much irritation? I suspect the general public will cheer loudly if Pluto is restored.
It’s not just Pluto. A host of new “planets” would have to join the big ones already recognized.
As of February 2017 over 2300 Trans-Neptunian Objects appear on the Minor Planet Center’s List of TNOs. By late last year, 242 of these have their orbits well-enough determined that they have been given a permanent minor planet designation. So you can see the problem.
Pluto was demoted not just because we discovered how small it really is, but because the list of “planets” would eventually have to reach hundreds if not thousands in the solar system if it were still designated a planet.
We’ve known the size of the solar system for quite a while now.
All of those tiny insignificant ice specks discovered by Americans. And that above all other facts is the determining factor in this retroactive push for new definitions of what is or isn’t a planetas.
Bigotry was invented by Europeans after all.
PS: It’s unclear how many minor planets would eventually rate as dwarf planets, but the overlap is large.
Euler diagram showing showing types of bodies in the solar system:
Nice diagram. Are the box sizes by number or by mass?
If by number then dust ought to dwarf everything else. Followed by rocks too small to discern by sweeping telescopes.
If by mass, where’s the Sun?
Euler diagrams represent sets. The boxes don’t denote either mass or number of members, just that there are larger or small numbers of intersections.
Thanks. I learn again. Twice in a week you have shown me something new.
So basically this is showing that planets are defined as being planets only; planets are not anything else.
The fact that they are not “satellites (natural)” is a special definition. They are actually satellites of the Sun.
Comets are defined as not being “minor planets”. OK. That feels right. But I can’t quite say why.
And there ought to be a box for “Stars” to hold the Sun. In some systems it would represent more than one example (as seen on Tatooine).
M,
You’re right, but this diagram is just for bodies in the solar system that aren’t the sun.
Overlapping sets occur, as for instance with Ceres, which at a minimum is an asteroid and a dwarf planet. Pluto is a KBO, a TNO (most of the time) and a dwarf planet.
Comets aren’t minor planets because their orbits are highly eccentric and they haven’t cleared out their own paths through the solar system, which is why they have the disturbing habit of colliding with planets and other objects. Think Comet Shoemaker–Levy 9.
The point about comets clearing their orbit is not persuasive (the eccentric orbits makes sense).
You mention Ceres. It certainly feels like the same sort of thing as Pluto. Very Dwarf Planety.
But look at where it lies. Is the asteroid belt split into two fields? So dwarf planets don’t need to clear their orbit. But nor do actual planets.
The original article is wrong, as I wrote in my first comment on this thread. Over 100 planets in our solar system misses the point of planets.
But the argument that “clearing the orbit” is necessary to be a planet is too tight a restriction. Definite planets don’t do that.
And it means that objects can attain planet status with time and collisions. That seems wrong.
Seems a bit confusing.
We have centaurs, dwarfs, neptunes and even more than one of Santa’s comets.
Are there more than one dancers? Are they a subset of the comets?
Shouldn’t they be a subset of the Rudolf’s?
/sarc, with apologizes. 😎
Maybe planetness is like the court’s definition of pornography. You know it when you see it.
Terrific logic aid. Plus 10.
Where do the rings go?
Hank,
You hearken back to M’s comment about dust.
The rings are mostly chunks of water ice, so don’t rate a category. They vary greatly in size, and can incorporate dust and even rock, but range only from dust particle to mountain-size.
Ristvan,
Glad you found the Euler diagram useful. It’s subject to change, of course, but current at from AD 2006.
Correction:
Smallest Saturn ring particles are the size of sand grains, not dust, although they can incorporate dust.
Jupiter too has rings.
M,
Regarding clearing their orbits:
Pluto is only 0.07 times the mass of the other objects in its orbit. Earth, in comparison, has 1.7 million times the mass of the other objects in its orbit.
Thus, the odd asteroid crossing the orbit of or centaur cluster coorbiting with a planet just doesn’t matter, when the difference in mass as a share of all mass in the orbit is on the order of ten to 100 million-fold.
Now that makes sense.
A planet is x times larger in mass than all the other things that are regularly in its orbit. And I mean “regularly” literally.
I would put x at 100. But any arbitrary number would do. It would be measurable and decisive.
Hmm. This rules out Counter-Earth planets. A same size planet orbiting the same distance but on the far side of the star. It must appear somewhere in the universe.
Alternatively a planet is just an historical label given to the most culturally important objects orbiting nearest a star.
M,
Originally “planet” just meant “stars” which wander, instead of appearing fixed. Discovery of the true nature of the solar system, galaxy and universe has forced astronomy to come up with new, more accurate nomenclature.
True planets and Pluto and other dwarf planets are “round” and in direct orbit around the sun. What they lack is “clearing their neighborhood”. As you note, the threshold for “clearing” isn’t defined, but doesn’t really need to be, since in all dwarf planet cases so far, the gulf between planets and dwarf planets is enormous in this criterion.
Times 100 would be a good threshold, but given the enormity of the difference between present planets and dwarf planets in this regard, even 1000, 10,000, 100,000, a million or ten million times would suffice.
IMO a KB object of planetary mass, such as Mercury, would have already cleared its neighborhood, thus achieving planetary status. As the outer solar system is explored, such far out planets may be found.
If “planet” is a status that is obtained through time, rather than size or trajectory, then it doesn’t seem to be a suitable definition. To me, at least.
And for “planet” to be useful it must apply to solar systems other than our own. Just as The Sun is a special name in our home system while “star” is general, “Earth, Mars, etc” are special names in our home system while “planet” should be general.
I refer again to my Counter-Earth example. That can never be a “planet” or two. But if they both evolved humanoids then they would both be more planety than Mercury.
Frankly, what definition of planet can include lumps of rock, lumps of frozen gas and NOT lumps of frozen water?
More I think about it, More I think “planet” is an archaic and obsolete term.
IMO “planet” in its modern definition works well for other star systems as well as our own. All exoplanets discovered so far meet all three conditions of the IAU for “planet” status, whether rocky like earth or gaseous like Jupiter.
Under no rational system are Pluto and Mercury equivalent, let alone Jupiter and Pluto.
The inner rocky planets are in effect equivalent to the cores of the outer gas and ice giants. Pluto, Ceres and other dwarf planets, by contrast, could never even constitute planetary cores. They are, like comets and asteroids, tiny mixtures of ice and rock. Even Mercury is rock and metal, like the cores of the other inner planets and even the outer ones.
Umm.. does it matter?
Does it matter the name humans call something – it doesn’t change what it is, it exists..
It’s purely an arbitrary decision – like “x” is a galaxy and “y” is not – no one else in the galaxy cares what humans call something.
Now – if Plutonians turn up and say they are offended that we don;t call Pluto a planet – sure, redefine it.
It’s a planet… simple as that… what else does it matter?
The size of the problem isn’t improved by adopting qualifications on what constitutes a planet that in fact should also disqualify some bigger inner planets. It would be perfectly straightforward and meet Chimp’s reasonable concerns atbout the hordes of minor objects awaiting us by just ruling that objects beyond Pluto will not be classified as planets. Frankly astronomers could worry themselves into nervous breakdowns if they are going to be fretting about how many categories of odd, small or strangely orbiting objects they are going to find in the Kuiper belt. And who knows, there may be a few more surprises that will tax whatever definitions we devise.
Yeah like dyson spheres or the orbits of orbiting-bodies around binary stars! There are more things in heaven and earth, chimp, than are dreamt of in your philosophy. Just Imagine the stuff we’ll see caught in lagrange points. Where is Oilerman going to fit in the exo stellar planetary fuzz.
Which is my point.
Pluto is not a planet. If it is, then all the as yet undiscovered TNOs bigger than it will also have to be planets. Kids are not going to learn the names of 8000 planets. Eight are hard enough for most, even though all but two of those are visible to the naked eye.
Uranus is alleged to be naked eye visible, but I’ve never been able to see it. Of course, I’m near sighted. Somehow observers with normal vision and even far-sighted never managed to notice it (or identify it as a planet, ie a “wanderer”) for the whole 200,000 years of modern human existence, until Sir William Herschel.
Couldn’t we just invoke a grandfather clause? It’s been a planet all my life and hasn’t changed.
See my comment at March 19, 2017 at 8:10 pm: I propose Honorary Planet, in memory of Percival Lowell. /Mr Lynn
Honorary Planet is a good suggestion, excluding all the other dwarf planets. Except what about Ceres, predicted in 1772 (or 1766 or 1596) and observed in 1801, but soon rejected as a planet?
Earth, moon and Ceres:
Pluto compared:
http://i.imgur.com/LoHgwfZ.jpg
[Equally important, what is Mercury to that same scale ??? .mod]
Left to right for the little guys is moon, Pluto, Charon in left hand image.
Ceres never achieved the celebrity of Planet X, or Pluto. /Mr L
With the ever slimmer slices scientists are taking, what can survive ?
Both originally “discovered” in 1930.
Coincidence?
I think not.
http://pbs.twimg.com/media/CJ4ejHkUsAAEAnm.jpg
That portion of IAU’s 2006 formula – which required that a planet and its satellites move alone through their orbit – excluded Pluto. – IAU
Yeah, well, Charon was discovered in 1978, long before the IAU came up with this specious nonsense, and Hydra and Nix came along in 2005, never mind the separate, if eccentric, orbit of Pluto and its (now five) moons. So the IAU’s so-called definition is either baloney. And that brings up Titan, a ‘moon’ of Saturn. It’s bigger than our moon, bigger than Mercury, has an atmosphere, liquid bodies (methane and nitrogen) and seasons. So Titan almost qualifies as a planet on its own, except that it doesn’t have any moons in orbit around it, and doesn’t orbit the central star.
I think this is another case of much ado about nothing.
NASA better leaves that commerce to
https://www.google.at/search?q=esa&oq=esa&aqs=chrome..
Titan and Jupiter’s larger Ganymede rival Mercury in diameter but not in mass. They are only about 40 and 45% as massive. The IAU could have saved themselves a lot of discussion by simply saying any object orbiting the sun (less its natural satellites) in approximately the plane of the other planets, with mass greater than Mercury’s is a planet.
Ya know? My first impulse after reading the headline was thank you Dr. Trump for giving us the opportunity to discuss something going on in science besides CO2. What a blessing, this guy is proving to be. imo
This guy deserves more respect, though I like the guy, he is our president. More respect is due, even if he was my neighbor.
This fellow is pushing this because of activism. Sounds dumb, because it is. The early astronomers had it about right. No need to deconstruct everything. They will end up creating classifications similar to those currently in use, only with silly names or numbers. Planet means wanderer, yes? That is a splendid name and meaning.
http://cf.ltkcdn.net/interiordesign/images/std/128508-286×400-jsw_old_outhouse.jpg
Should we call it a house – or is it really just a Trans Residential Object?
Point well taken.
Definitely not a house. But I might suggest Post-Residential Object.
In the South, they’re often called backhouses rather than outhouses.
Or maybe Out Cloud Object.
Just the “Little Brown Shack Out Back”:
For those who prefer the TL;DR
I know, Pluto is a planet, because it has always been a planet and always will be.
/rant
1) Pluto is a planet because of the historical connection first discovered in 1930, by Clyde Tombaugh
2) Pluto is not a comet, The definiton of a comet is: “a celestial object consisting of a nucleus of ice and dust and, when near the sun, a “tail” of gas and dust particles pointing away from the sun.” Pluto has not produced a “tail”, has not approached the sun sufficiently enough for a tail to form. Also Pluto has a density of 1.86 and “Pluto’s internal structure is differentiated, with the rocky material having settled into a dense core surrounded by a mantle of water ice.”[Wikipedia] NB: water ice sould be Nitrogen ice (contradiction in Wikipedia articles)
3) All planets move in elliptical orbits, with the sun at one focus. This is one of Kepler’s laws. The elliptical shape of the orbit is a result of the inverse square force of gravity.[Google: elliptical orbits]. Yes Pluto does have a higher eccentricity. So What! Therefore you cannot use eccentricity to define a planet.
4) Every planet has an orbital inclination, which “measures the tilt of an object’s orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object”.[Wikipedia: Orbital inclination]. Yes Pluto does have a higher orbital inclination. So What! Therefore you cannot use orbital inclination to define a planet.
5) The definition of planet set in Prague, Czech Republic in August 2006 by the International Astronomical Union (IAU) states that, in the Solar System, a planet is a celestial body which:
a) Is in orbit around the Sun,
b) Has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and
c) Has “cleared the neighbourhood” around its orbit
The planet Pluto satisfies a) and b) above. But not c), according to the IAU definition of a planet. However, “he wording of the final draft of the definition has continued to be criticized, primarily in the United States. Notably, Alan Stern, the lead scientist on NASA’s robotic mission to Pluto, has contended that Earth, Mars, Jupiter, and Neptune have not fully cleared their orbital zones, just like Pluto. Earth orbits with 10,000 near-Earth asteroids. Jupiter, meanwhile, is accompanied by 100,000 Trojan asteroids on its orbital path. Stern has asserted: “If Neptune had cleared its zone, Pluto wouldn’t be there. [Wikipedia: IAU definition of planet]
Some people have countered with a different opinion. However, as Stern pointed out above, Earth Mars, Jupiter and Neptune have not cleared there orbits, therefore IAU definiton of a planet c) is contradicted. Therefore Pluto is a planet. Because there is contention or controversy surrounding definition part c) of a planet.
6] The scandal surrounding the number of people who voted 424 (last day of conference) against the total membership of the IAU, is a farce. All members of the IAU should have a vote on something important as the status of the planet Pluto. Regardless of whether they are involved in planetary research areas or not. A consensus (sic) of all 10,000 members should have been taken. Because of this vote, farce, scandal, whatever you want to call it, Pluto is a planet.
/endrant
Regards
Climate Heretic
PS Did I tell you that Pluto is a planet?
PSS I will continue to teach that Pluto is a planet 🙂
Then what about Ceres, Haumea, Makemake, Eris and Sedna? And even bigger dwarfs to be found in the future? Will you also teach that they are planets, too, even when they number thousands?
As I noted, had Pluto been observed first in 1980 rather than 1930, it wouldn’t have been considered a planet, as it is too small. It was granted planetary status because Tombaugh couldn’t distinguish Pluto from Charon.
It is true that American astronomers were more supportive of Pluto than those from other countries, it being the only putative “planet” discovered by an American.
Ceres was briefly considered a planet, but astronomers concluded it was too small to qualify.
Chimp said: “Then what about Ceres, Haumea, Makemake, Eris and Sedna? And even bigger dwarfs to be found in the future? Will you also teach that they are planets, too, even when they number thousands?”
Corrected: “And WHAT IF even bigger dwarfs are to be found in the future? Will you also teach that they are planets, too, even IF they number thousands?”
The answer to all is YES!. What, you haven’t memorized the Periodic Table of elements yet? Or the names of all the rivers on planet Earth? Surely we need a better way of defining “mountains,” or at the least “mountain ranges,” because no one can remember them all?
The problem with (c) of the IAU definition is huge: move Mercury to Pluto’s orbit & it is no longer a “planet.” Move Earth to Sedna’s orbit & it is no longer a “planet” either. Suddenly, one realizes that meeting or not meeting (c) involves calculating a fairly complicated, non-intuitive mass/distance/age ratio, rather than observing something definitive or observable about the object itself.
But this isn’t even the largest, most obvious problem w/the IAU’s garbage “definition.” Point (a) says the object has to orbit our Sun! Really? “Sorry, the rest of the universe: no planets for you?” Worthless.
The new definition needs to be modified to recognize that many of these “planetary” objects are also “moon,” and should primarily be referred to in that way. This would reduce the proposed ~110 or so “planets” to a little more than a dozen… & even I can memorize THAT many state capitals!
It’s not what if, but when. There are already hundreds of minor planets awaiting more details to determine whether they are dwarfs or not.
A planet isn’t akin to rivers, or even the elements. They’re more like continents, which are distinct from islands. A few islands are on their own small tectonic plates, so that they’re in a gray area.
Smokey,
If you moved Mercury to Pluto’s orbit, it would rapidly attract enough of the Kuiper Belt objects in its orbit to crash into it, or fling them out of its path, so that it would indeed again become a planet in its own right, since it is about 2.5 times as massive as Pluto.
In your geological or geographical analogy, I equated planets with continents because they are the highest order subunit in each case, ie solar system (less sun) and earth. Well, most oceans cover more area than most continents, but you get the idea. Equating planets with features like rivers is a false analogy.
Chimp said, “In your geological or geographical analogy, I equated planets with continents because they are the highest order subunit in each case, ie solar system (less sun) and earth. Well, most oceans cover more area than most continents, but you get the idea. Equating planets with features like rivers is a false analogy.”
With respect, Chimp, I think you’ve missed most of the analogy: rivers, mountains, countries, states (& their capital cities) occupy a huge amount of space on Earth’s surface when compared to that which even the “true” planets occupy in the solar system. As such my analogy stands. We don’t need to scale up to continents or oceans because that would be akin to re-labeling the entire “inner solar system” or “the asteroid belt;” we’re not labeling areas or volumes, we’re labeling objects within those volumes… to say nothing of the fact that we already have labels for those. (The Kuiper Belt, the Oort Cloud, etc.)
Also, you’ve ignored the other problems I brought up with
Mike Brown’sthe IAU’s deliberately anti-Pluto definition (for no other explanation can reasonably exist for such a flawed, provincial description) to focus once again on the “arbitrary upper limit” objection to Dr. Runyon’s definition. I’ve already stated that I don’t believe “moons” should be included, regardless of size, yet even so: if there end up being 20,000 objects that can objectively be called “planets” in our own solar system by itself, so what? There are already known to be more asteroids & comets than that arbitrary figure in our system, by more than an order of magnitude: should we re-define the those terms as well because there are ‘too many’ of them?Finally, to extend my previous analogy, there are mountains, volcanoes, ridges & scarps on many other planets besides Earth; are we going to continue to pretend (as the IAU’s definition does in the case of “planets”) that those features/formations don’t occur via similar processes elsewhere in the universe? For instance, should we be calling Olympus Mons and Tvashtar (e.g.) “exovolcanoes” because only “real volcanoes” occur on Earth? In the same way, planets occur throughout the universe, not just in our own solar system, no matter that the majority-of-the-minority vote of the IAU decided otherwise.
As far as the argument that “Mercury would have cleared that orbit by now,” are you sure? have you run the math from the alleged beginning of the solar system to see if in fact that slight mass advantage really does “clear” Pluto’s orbit in the time allotted? Because, just eye-balling it, I don’t think it does, & I KNOW Earth doesn’t clear an orbit much past Eris, let alone at the distance of Sedna (my previous reference).
Regardless, this idea that a “planet” has to have been around for a certain period of time before it can even be CALLED a “planet” is silly; either it’s a planet or it is not. The amount of time it’s spent in a given orbit is a curiosity, not a defining characteristic of the object (likely saying more about the system in which it formed than about the object itself), nor is it one we can figure with any great accuracy, even for objects in our own solar system (cf. several recent papers alleging that our planets may have shifted or even swapped orbits in the fairly recent past relative to the age of our solar system, i.e., within the last 1 – 3 billion years).
Pluto’s eccentricity is about 15 times as great as Earth’s and three times Mars’.
The discovery of Eris in 2005 is what prompted the IAU in 2006 to define “planet”. It became obvious that Pluto was going to be eclipsed repeatedly by bigger and better TNOs, possibly in their thousands.
I know, but others were thinking it! The real point is context is often important in a definition, how many argued against helocentrism because it would necessarily change the status of Sol and Luna?
If there are 110 planets, how are little kids going to be able to remember all of their names. With 9 we had mnemonics like: “My Very Easy Method Just Shows Us Nine Planets”. 110 seems to be out of control.
https://en.wikipedia.org/wiki/Planetary_mnemonic
Think Of The Children!.
Then: My very eager mother just served us nine pizzas.
Now: My very eager mother just served us NUTHIN’.
With enough children to eat nine pizzas, my very eager mother just served us NOODLES.
Oh yeah, and where do the Dyson spheres fit in?
Some words don’t need a really great definition. Pluto is a planet because at the time it was given it’s name it seemed so and the people all started calling it such. Other things that seem close we can just call planet-like objects until something better comes along. It’s presumptuous to name something a planet and then try to take it back. It may even be a micro-agression to say that Pluto isn’t a planet because it’s a dwarf planet. Did you clear that one with the IDU (International Dwarf Union)?
Can anyone please tell me what difference calling Pluto a planet or a minor planet will make to the life of anybody?
Richard
@richardscourtney: It’s not about Pluto, however much the media & the IAU want to make it sound like it is. Pluto is the object “everybody knows,” so that’s how the discussion is framed in the popular gestalt. That’s it.
Rather, it’s about having a useful scientific term with which to categorize various objects we see in the universe. Whether Pluto happens to be “planet,” “ice dwarf” or “cartoon character” is, in & of itself, immaterial; having a useful, scientifically descriptive label that actually means something is the important thing.
Can I just be the first to say that, since it was pointed out to me, I can’t stop seeing the face of Disney’s Pluto in Pluto’s Southern hemisphere?
I love the contribution by Kwarizmi of a trans residential object . it is the absurd definitions and deviously arranged vote to demote Pluto that caused this needless fuss. Chimp’s defence of the definitions used to end Pluto’ s status are not very persuasive precisely because they apply in equal measure to other planets which no one wants to disqualify. No one is advocating or is seriously going to try to learn 8000 planet like body names. If your definition is rubbish choose a better definition or just set an arbitrary cut off like we stick with the planets most people are comfortable with (as evidenced by many of the comments). And I still don’t see why those of us interested in Astronomy wouldn’t be comfortable with knowing the names of a few extra large bodies beyond Pluto if they turn up – even if we agree not to call them planets.
Perhaps in addition to calling Pluto an Honorary Planet, as I suggested above,
https://wattsupwiththat.com/2017/03/19/scientists-try-to-restore-plutos-planet-status/comment-page-1/#comment-2455468
we could designate the other large Trans-Neptunian Objects as Aspiring Planets, or maybe just Wannabes.
/Mr Lynn
They have already turned up, and more will be added every year.
If you’re OK with 10,000 planets, then by all means embrace Pluto and those larger dwarf planets already known.
The inner planets count as planets just as much as the outer giants. Pluto, not so much. Nor Ceres, which for part of the 19th century was considered a planet, but rightly down-graded.
Latest update on dwarf planets from the world’s leading dwarf planet hunter, Caltech’s Mike Brown:
http://web.gps.caltech.edu/~mbrown/dps.html
As of Thu Jan 5 2017, there are:
10 objects which are nearly certainly dwarf planets,
30 objects which are highly likely to be dwarf planets,
75 objects which are likely to be dwarf planets,
148 objects which are probably dwarf planets, and
703 objects which are possibly dwarf planets.
Hence, dwarf planets already outnumber planets and will soon be on the order of 100 times more plentiful, headed toward 1000 times.
Second largest asteroid Vesta is also probably a dwarf planet, but a collision knocked off a big chunk of it, so that it is no longer round enough to qualify.
https://en.wikipedia.org/wiki/4_Vesta
But it is a minor planet.
IMO these definitions are good.
In my view, there are four planets, Jupiter, Saturn, Uranus, and Neptune. Everything else, including
Mercury, Venus, Earth, Mars, Pluto, and Charon, is a planetiesimal.
FWIW, I have expanded my comment yesterday into a blog post, and quoted some of you (with links). See here:
https://walkingcreekworld.wordpress.com/2017/03/20/pluto-the-honorary-planet/
Thanks for the intriguing discussion. I even learned something about mammalian evolution here (I’ll save that for another post).
/Mr Lynn
Pluto was named for the god of the underworld because it was beyond Neptune when discovered. It was misnamed. The “real” Pluto has yet to be discovered. The current one should be renamed Salacia and its moon Venilia.
Whenever we were to decide to install outerposts to observe our solar system or the environment of our solar system, we would anchor these outposts on or around the planets.
With this simple intuitive access, a maximum of 9 so-called planets remain in our solar system.
Can’t believe no “Rick and Morty” clips on the Pluto debate!
The term “Dwarf Planet” does not pass politically correct “filters” it should be called “Size Challenged Plant”.