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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The IAU didn’t make Pluto a non-planet but a minor planet, along with other objects in its zone, like Sedna, and with asteroid Ceres.
Exactly. I thought it was re-classified as a “dwarf planet”.
“There’s nothing non-planet about it.” Well , apart from all the qualities like not clearing its orbit, that the IAU had decided to use as criteria. Maybe there is more to astronomy than landscapes.
Anyway, the main point of demoting Pluto was to ensure that there were still nine planets when they get around to identifying the large TNO whose existance is becoming more and more accepted. We would not want to have to admit that there really is a “planet X” would we?
Nine planets, 57 states. Go Pluto.
Greg,
There might be more than one planet-sized object out there in the far reaches of the solar system:
http://www.universetoday.com/42450/planet-x/
For that matter, there are interstellar planetary mass objects, orbiting the barycenter of the galaxy rather than a star. Probably lots of them. They might constitute a big chunk of the ordinary (baryonic) dark matter.
I should have written dwarf planet.
It’s estimated that 200 dwarf planets probably inhabit the Kuiper Belt, with up to 10,000 possibly lurking farther out, scattered around toward and in the Oort Cloud.
https://en.wikipedia.org/wiki/Dwarf_planet
Only about a half dozen dwarf planets are currently known, with more likely candidates awaiting further study.
http://zidbits.com/wp-content/uploads/2011/04/Dwarf-Planets.jpg
Well, if clearing an orbit is part of the definition of a planet then Jupiter fails because it has about 5000 Trojan asteroids in its orbit at the Lagrangian points. Neptune & Mars also have some Trojans and even the Earth has one (2010TK7). So the Earth is not a planet either following the IAU definition I would have thought! Pluto is a planet, not a dwarf planet.
But I do think moons are different from planets…planets orbit stars, not other planets. Moons can orbit planets and asteroids and maybe comets(?).
Think of the natural resource possibilities on all these rocks in our solar system. All we have to do is survive going to get them.
Alastair,
The IAU’s third criterion actually says “clearing its neighborhood”. Co-orbital centaurs don’t count.
https://en.wikipedia.org/wiki/Clearing_the_neighbourhood
I think they prefer to be called “little planets”.
But they also said a dwarf planet is not a planet. (Think of it as a two-word noun instead of an adjective and a noun.) Yes I agree it’s nuts. Pluto has two moons, an atmosphere (I helped discover it), seasons and weather. Something odd about saying that’s not a planet. And their definition involving clearing its path gravitationally means that exactly the same body would be a planet if it orbited at one distance, but not at another. That’s really odd.
Ron,
Having an atmosphere doesn’t matter. Ceres might have not just an atmosphere but an ocean. Many moons have atmospheres, some dense, and probably oceans.
PS: Pluto presently has five known moons, but that still doesn’t make it a planet. Asteroids have moons.
Pluto restored…Mickey, Minnie & Goofy will be pleased.
roflcopter!
Magic!
I, too, rotflmao!
Auto
OK, I support returning Pluto to planetary status but I don’t see is as an improvement to create a definition which ignores the common sense category of ‘moon’. We should recognize the planetary character of large moons, asteroids and rogue wanderers based on their intrinsic qualities but the neighborhood in which they are situated is also important, distinctive and should be acknowledged even if it could be transitory.
Agree with you, Dean.
Pluto is obviously a planet,with two moons orbiting it.
Earth is a Planet,the with a Moon orbiting it.
It has more than two moons, but that doesn’t make it a planet. Some asteroids have moons.
Pluto is certainly not a planet. Pluto – Charon makes some case for being a binary planet (based on an external barycentre). Pluto on its own is not.
The Moon being a planet? The idea is absurd. Being spherical doesn’t make a planet. Never has. Never will.
Andrew, one of the proposed new planetary definitions I heard would indeed turn several moons into planets. For some odd reason, that particular definition did not include “orbits the sun”
If you suggested that having a moon should be *required* for a planet, it’s a rather radical idea. After all, Mercury and Venus – two of the more “core” or characteristic planets – don’t have any moons. Some people really seem to be irrationally obsessed with Pluto. It’s just a round of a rock that is very far and there are numerous rocks like that which weren’t known. On the other hand, Mercury, Venus, and especially the Moon are things we can see rather easily on the sky. Changing *their* status is an invitation for a civil war.
Getting my kids to memorize the order and names of 8 or 9 planets wasn’t too hard, but for 110 would be Herculean.
Unless we name them numerically. We could just call Earth ‘3’, lol. you could recite millions.
Jeff,
Except that they sometimes switch places. Pluto’s orbit is so out of whack (for a planet) elliptically that sometimes it’s inside of Neptune’s.
I guess that would make it a Cis-Neptunian Object, even though it was the first Trans-Neptunian Object to be discovered.
A real switch-hitter, definitely in need of a multi-sex bathroom.
If we were to include moons as planets, how do you go about defining the order?
I agree that “planet” should be defined in terms of an object’s intrinsic properties for two reasons.
Firstly, now that we can detect exoplanets and measure some of their properties we need to use terminology that will function consistently across all stellar systems. If object X is classified as a “planet” in system A but identical object Y in system B is classified as something else because of “external factors such as its orbit or other objects around it” then that will only create confusion. It makes it harder to compare the prevalence of particular types of object across different systems and makes it harder to describe them clearly.
Secondly, the use of “external factors” means that an object might be classified as a planet at some points during its existence but not at others, depending on changes in its orbit or the conditions around it.
However, we also need to recognise that the word “planet” is obsolete. It originally referred to objects that appeared to move in regular cycles relative to the “fixed” stars. It was invented by people who could only see a few of the objects that actually exist in the solar system, and who therefore assumed that these few must represent a particular and important category. But we now know that there are a huge number of objects in the solar system, with sizes ranging from vastly bigger than the Earth down to tiny rocks. There is also a huge variation in composition and structure, even among those objects that have been traditionally known as “planets”.
Therefore, it becomes increasing difficult to draw any meaningful diving line between “planets” and other objects, and there is less and less value in trying to preserve a category that originally meant no more than “we can see it and it moves”. The same argument can be applied to “asteroid”, “comet” and other popular terminology. It’s obsolete because it originated as a description of how things appeared to the human eye and through small telescopes before we were aware of the full range of objects that actually exists in the solar system.
So, what we really need is a system of classification for non-stellar objects that can be applied consistently across all stellar systems and to objects that do not orbit any star. It would therefore need to define them in terms of their intrinsic properties and would give them a classification code rather than a name. I’m imagining something a bit like a Hertzsprung–Russell diagram for discrete non-stellar objects.
It would probably still be necessary to retain archaic words like “planet” as a description of particular types of object within that classification system. But it would no longer matter if the definition of the word involved an arbitrary combination of characteristics, because it would just be an arbitrary term that was used to assist in mapping the terminology used in previous scientific literature to the new system and as an aid to understanding in popular science. The word itself would no longer carry any weight as an analytical category.
AndrewZ
“If object X is classified as a “planet” in system A but identical object Y in system B is classified as something else because of “external factors such as its orbit or other objects around it” then that will only create confusion.”
I think we have to admit that what astronomers think and say is not what ordinary folk think and say and there is lots of room to allow the regular people their voice. Why, for example, should there not be a popular vote on what to call Planet X? It should not fall to a couple of astro-nerds.
I am with the groups above who what large objects that shine, not twinkle, to be called planets and the things orbiting them to be called moons. Objects that orbit moons should be called satellites.
I don’t mind giving the asteroid belt members names but they are not planets because the whole lot of them is in fact a broken up planet that has no name, yet. It is unlikely to re-assemble much of itself in the lifetime of humanity.
Pluto is a planet with a couple of moons. Perhaps we can go as far as naming Planet X, but Oort Cloud members? Put a minimum orbital time on the definition and they are separated into Oort Cloud Objects and Planets. The public can live with that.
I’ve always thought that the rule should be:
Whoever discovers it, gets to name it.
Planets orbit stars, moons orbit planets, so I don’t get the point of calling Europa a planet. That’s just silly, so everything else he says can be dismissed.
That apparently is too simple a definition. If asteroids happen to share the orbit, are they planets? However, increasing to 110 planets is far too complex. I’m sure there’s a better way.
You know he is actually right about Earth, Mars, Jupiter and Neptune sharing their orbits with asteroids.
That means that Earth, Mars, Jupiter and Neptune are not actually planets, yet.
But they will be when they sweep their orbits clear.
He has a good point that this definition is inadequate.
But a definition that lets everything in – 100 plus planets – still misses the mark.
If the other objects are in LaGrange points, can the orbit ever be swept clean?
I would think that LaGrange points are a special case and a populated LaGrange point would lend weight to planetary status.
After seeing it up-close, it looks likes it should be re-classified back to a planet.
Its composition is more like a comet than a planet.
True of the surface, but does it have a core of rock? More observation = more questions…
No it’s not. Pluto’s internal structure is differentiated, with a rocky material at the core surrounded by a mantle of water ice and a crust of nitrogen ice. The diameter of the core is approximately 1700 km, 70% of Pluto’s diameter.
Regards
Climate Heretic
Comets also have cores of solid rock:
http://universe-review.ca/I07-08-comet.jpg
It would be fun watching Neil deGrasse Tyson throw a hissy fit if Pluto is restored.
+ a lot
Auto
I always thought that for celestial object to be a planet it has to be orbiting a star. So something like Moon could never be a planet cause it doesn’t orbit a star, no matter how large it is. But what do I know?
Apparently quite a lot.
If you “ignore” the earth, the moon makes a fancy pie crust edge motion around the sun (Sarc? )
The great Isaac Asimov wrote an essay called “Just Mooning Around” in which he showed that the Moon is more strongly attracted by the Sun than the Earth. That is, it primarily orbits the Sun. See https://en.wikipedia.org/wiki/Tug_of_war_(astronomy) and http://www.math.nus.edu.sg/aslaksen/teaching/convex.html He argued that this would make the Earth and Moon a double planet, which I rather like.
The sun’s gravitational field deflects the earth/moon system about 1° per day. The earth’s field deflects the moon about 13°. I’d say the earth wins that one.
Mike McMillan
Agreed.
But I still like the ‘double planet’ idea.
Auto
The distance ^2 term wins most times.
If the barycenter falls within the the mass of the larger object, the smaller object is a moon. If the barycenter falls betweeen the two masses then it is a double planet.
The earth/moon is a planet/moon system.
(my definition only. made up by me. not approved by anybody else.)
DonM, according to your definition: “If the barycenter falls betweeen the two masses then it is a double planet” that would make the Sun-Jupiter system is a “double planet.” “Jupiter’s mass is 2.5 times that of all the other planets in the Solar System combined—this is so massive that its barycenter with the Sun lies above the Sun’s surface at 1.068 solar radii from the Sun’s center.” reference: https://en.wikipedia.org/wiki/Jupiter#Mass_and_size
David,
I would say my made up definition of dual planets, based on barycenter, doesn’t include suns (or black holes) as planets.
The Earth Moon barycenter orbits the Sun.
The Sun orbits the barycentre of the solar system.
The sun moves in the Milky Way, so the earth and moon move in a corkscrew.
Charon and Pluto form a dual planetary system, since their instantaneous point of rotation in between both bidies. They are orbiting each other.
I agree that the moon is a satelite of Earth, but that doesn’t necesarilly exclude it from being its own planet. This new definition only states that satelites can also be planets if they are massive enough. I see no problem with that.
The argument about learning all the planets, is stupit, our kids shouldnt have to learn all 100+ planets, just the classical list is plenty.
Sebmagee
The problem with that approach is that the barycentre of the solar system sometimes sits outside the radius of the solar surface.
I see no problem with calling the larger member ‘planet’ and the smaller one ‘moon’. If there is to be a ‘rule’ let it be that the moon has to be more than 50% of the mass of the planet to be counted as a binary planet. The reason this is a better approach is that a modestly sized moon that orbited at a good distance away would place the barycentre outside the planet’s radius. Our moon, moved away not too much more, would achieve this. At the moment it is 1000 km down from the Earth’s surface.
You know scientists have no meaningful research to do when they start publishing papers arguing about the definition of things like this. The definition is subjective. It isn’t like these things are part of an equation in which the exact units of measure are critical.
There’s some small rocks and some big rocks circling the sun. Draw the line where ever you want. But padding one’s resume with “research” papers funded by the public dime to argue where the line should be? This is the stuff of PhD’s now?
Definition, categorization and description of transitional states have always been part of the business of science.
Should they be changed for PR purposes?
Ironic, which institutions are involved (again).
>You know scientists have no meaningful research to do when they start publishing papers arguing about the definition of things like this.
Their funding for making up climate change stories is drying up.
Earth and Moon are in binary-orbit; both Earth and Moon orbit the Barycenter. The Barycenter is located about 4,671 km from the Earth’s geocenter-mass and center-of-figure, within the upper mantle (Earth’s ellipsoid-figure radii are 6,378.137 km [major – equatorial] and 6,356.7531342 km [minor – polar]). There is an animation of the Earth and Moon orbiting the barrycenter:
The Barycenter-orbits of Earth and Moon with axial rotations (Moon is in a locked orbit) and their orbit around the Sun produce the Equation of Time, a component of the Analemma, as viewed from Earth.
What this means, conjecture, is that the NASA Apollo Program, which was advertised and marketed as a “Voyage To The Moon” and grammatically correct was in fact a voyage to another Planet! Therefore, NASA need not do and Congress and OBM need not fund a “Voyage To A Planet (Mars) Beyond Earth”, because it was already done, almost 50 years ago! Ha ha! Now this is the way to “lower the bar” and cut Federal spending on wasteful “pie in the sky” programs.
For ref.
https://en.wikipedia.org/wiki/Barycenter
https://en.wikipedia.org/wiki/World_Geodetic_System
https://en.wikipedia.org/wiki/Equation_of_time
https://en.wikipedia.org/wiki/Analemma
A silly Through the Looking Glass Humpty Dumpty like poster.
Pluto was downgraded to planetoid for two very solid reasons. 1. Orbital plane is tilted 17 degrees from the orbital plane of the 8 true planets, which means Pluto did not form from the solar accretion disk process that places all true planet orbits in a single plane. Orbit is elliptical, which means it is a Kuiper Belt object. Kuiper also contains four other Pluto like (size, orbit) objects: Haumea, Makemake, Sedna, and Eris. All these planetoids are in off plane elliptical orbits. Just like the myriad of smaller elliptical orbit Kuiper Belt objects. Comets are of Kuiper Belt origin.
Ristvan claims, “Orbit is elliptical, which means it is a Kuiper Belt object.” According to that logic, the Earth is a Kuiper Belt object, because the Earth’s orbit is elliptical with an eccentricity of 0.0167.
Also Mercury is tilted 7 degrees from the orbital plane. Does that mean Mercury did not form from the solar accretion disk ?
PS… Mercury has an elliptical orbit with .208 eccentricity, also making it a Kuiper Belt object.
You have to orbit at least part of the time in the KB to be a Kuiper Belt Object.
DD, some astronomy science responses to your two refutatiinal comments. Perhaps will also help educate other WUWT readers on science nuances versus picayune objections. I reseached all this before initially posting. Space.com is but one apparently intelligent and reliable resource.
First, a star’s accretion disk is always thickest closest to the Star (basic math about angular momentum and gravitational attraction vectors– math challenged can google physics of accretion disks to,learn themphysics basics), so Mercury being 8 degrees out of ‘plane’ (none are in a literal plane) of the other 7 true planets is not surprising, rather it is likely. 8 degrees tilted closest to the Sun is not 17 degrees tilted farthest.
Second, I perhaps should have said Pluto has ahighly elliptical orbit. Of course Earth’s orbit is not a perfect circle. No planet’s is. But there are times when Pluto’s orbit is inside Neptune’s. Earth never goes outside Mars or inside Venus, and those orbits are much smaller, closer ‘circumferencial’ spacings. QED onnyhe geometry.
A science fail on pedantic semantic debating points. Please do better next time, as you are up against a former regional champion high school debater, later further honed at HLS.
I apologize for catching your errors. You made the claim that “Orbit is elliptical, which means it is a Kuiper Belt object” which is false. Being sloppy in your verbiage is not conducive to good science. Anyone that knows anything about astrophysics knows that no planetary orbit is circular. They all are elliptical. Lack of precision in language is common among non-scientists. Your 2nd error was posting: ” that places all true planet orbits in a single plane” (emphasis mine.) When someone in a debate makes a statement with the word “all” in it, the only thing a good opposing debater has to do is provide a single counterexample to destroy your claim. Mercury does this with regards to what you said about accretion disks. Lastly I could care less about your high school antics, the passage of time has not been good to you with regard to your debating skills.
“I apologize for catching your errors. You made the claim that “Orbit is elliptical, which means it is a Kuiper Belt object” which is false. ”
Dont forget Rud was a champion debator.
he only forget that science isnt a debate.
yes yes sometimes scientists argue. but science is not a debate.
The eccentricity of Pluto’s orbit is extreme, more like a comet than a planet. Its eccentricity is about 15 time greater than earth’s, as I commented previously, and around three times that of Mars, which is highly eccentric for a planet, due to its proximity to Jupiter.
Kepler used Tycho’s observations of Mars to determine that orbits are elliptical.
Rud is right.
A good example of the futility of terminological disputes. Clearly we’re now learning that the Solar System is not just a neat little paradigm of 9 planets and an asteroid belt, but a collection of hundreds of odd objects of varying sizes, some so distant that they are not observable until they sneak in close enough (e.g. comets). And there is no obvious evolutionary tree on which to structure a taxonomy. But we could use one, as we are now starting to investigate other stars and their ‘stellar systems’, or whatever they’re called. As AndrewZ says (March 19, 2017 at 8:50 am),
But absent such an agreed-upon classification (which will probably always be fuzzy), it is certainly more convenient for popular consumption, if not technical purposes, to refer to the ‘planets’ as those big objects that orbit the Sun (or a sun), and ‘moons’ as those (generally smaller) that orbit around other objects (usually planets) and not the Sun (or a sun).
So in this regard, it seems to me that poor ol’ denigrated Pluto ought to be restored to ‘planetary’ status, or perhaps Honorary Planet, since after all it was discovered by investigating the perturbations it caused in the orbit of Neptune, and that cannot be said of any of its putative congeners, like Sedna or Eris. Indeed the name ‘Pluto’ was considered particularly apt because the first two letters were the initials of Percival Lowell, and he should rightfully be allowed to retain his then-hypothetical planet, especially since his other famous hypothesis, about the canals of Mars, has been, sadly, disconfirmed.
/Mr Lynn
An orbits shape and inclination can be affected by interaction with other bodies.
Ristvan
I looked at the planetary orbits in the article we had on chaos the other day. Fantastic animation showing how the orbit of Venus sometimes moves out to be very similar to that of the Earth, and how much the Earth is jerked around by the planet’s. Mars also comes much closer to Earth than it is now.
My point is that we have no idea if Pluto is a true planet that formed in the same plane as the others. It may well have been and was yanked about and winged into its current orbital plane. Much stranger things are possible. It crosses quite near a huge object that could easily fling it about. If both were off their ecliptic at the time they passed near each other.
I think the primary school version of planets keeping their positions neatly is not a suitable framework for a discussion of the chaotic movements and large changes in orbits that actually occur.
Another meaningless argument about nothing. Does it really matter what Pluto is called? Sticks and stones will break your bones, but names will never hurt you.
The main real objection to Pluto as a planet, I believe, is it is the only one discovered by an American. The element ‘Columbium’ honoring Columbus’s discovery of America (okay, the the Norse beat Chris to it and today they’ve all been trumped by the ‘native’ people) but another international institute bullied in Niobium as official. Dang Yanks then went and created a couple of dozen more elements, so there!
In any case, a 100 more is a bit ridiculous. The idea that this will create more interest in planets is silly. Daffynitions by bean counter boring mucky mucks who never discovered anything (I call them ‘performance’ scientists like in music – in 350 yrs the great composers used up all the best note ((there are only 12notes and a few octaves)) and harmony combinations by the early 20th Century, same timing as scientific discovery).
Pluto identifies as a planet. Who are we to judge?
but whats its gender
We’ll know when it sends us a message and tells us.
If Pluto were a girl she would be called Persephone.
Well, since we’ve only observed (discreetly) and haven’t actually heard from it, I’ll hazard a guess it is not a female.
If it was a female or a very confused male-non-male, we would have heard plenty.
However Man (or Femailman) decides to define it, it is the rock it has always been.
“I want the public to fall in love with planetary exploration as I have,” Runyon said.
When you’re in love, you can’t get enough of it. QED
Still, restoring Pluto’s planet status sounds good to me. Rock on!
Runyon demonstrates the old adage:
“when you’re in love, size doesn’t matter.”
Plus many. Except that is not the main reason Pluto was demoted.
I have to admit that I like the concept of “all-inclusive”, but I don’t see how it will sell planetary exploration.
They are all HB’s (heavenly bodies). We can distinguish between HRB’s (heavenly round bodies) and others (asteroids, comets, etc.). I could see calling all HRB’s planets; that’s OK, even though it would include our Moon. I am glad Pluto is now again a planet, at least in this reckoning.
What seems to be most illustrated here is the extreme difficulty of trying to build a heirarchy for the various natural phenomena that works and makes sense. The same problem occurs in all sciences—as soon as an item is found that possessess characteristics of multiple catagories (it seems to be a planet, but it also seems to be an asteroid/it seems to be a mammel but it lays eggs) the system is threatened and/or falls like a Jenga tower. Trying to catagorize such complexity may be an exercise in futility. Humans just can’t imagine or think at that level yet.
There is no doubt that the platypus is a mammal. Mammals have three different ways of reproducing, but monotremes, marsupials and placentals are all members of Class Mammalia. Their ancestors all laid eggs.
Taxonomy isn’t hierarchical, although Linnaean categories still have some utility.
The IAU’s definition of planet is clearcut. That asteroids and other objects cross the orbits of the planets doesn’t obviate the definition.
Pluto has some traits of a planet and some of a comet, but is neither. Dwarf planet is a useful category.
It would never have been elevated to planetary status had it been known in 1930 how small it is. It looked bigger to Tombaugh because his telescope couldn’t separately resolve Pluto’s moon Charon. They are close enough to be tidally locked. The barycenter of their system lies outside Pluto. Smaller moons orbit this center of gravity farther out.
Pluto is not a comet. 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 the planet has a solid core of rock 1700km approximately in diameter.
In addition the IAU’s definitions 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 neighborhood” around its orbit.
Definition c) Is Not Clear Cut. Jupiter has the Trojan and Greek asteroids in its path. Therefore according to the IAU definiton of a planet, Jupiter is a dwarf planet.
For clarification I agree with the conditions a) and b) for the definition of a planet as listed by the IAU. Condition c) I vehemently disagree with.
Regards
Climate Heretic
What does “cleared its neighborhood” actually mean?
The situation in the Kuiper Belt and asteroid belt is fundamentally different from the orbits of the eight planets, including both the four little inner rocky ones and four big outer gas and ice ones.
Adapted from “Universe Today”, 2008, and updated:
http://www.universetoday.com/13573/why-pluto-is-no-longer-a-planet/
As planets formed, they became the dominant gravitational body in their orbit. As they interacted with other, smaller objects, they either consumed them or slung them away with their gravity. 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.
Any object that doesn’t meet the IAU’s third criterion is considered a dwarf planet. Thus Pluto is a dwarf planet. There are still many objects with similar size and mass to Pluto jostling around in its orbit. And until Pluto crashes into many of them and gains mass, it will remain a dwarf planet. Eris, Sedna and the other two dwarfs in the Kuiper Belt all suffer from the same problem.
I hope this clarifies the issue of “clearing”.
Sheri, IMO a very insightful comment. Taxonomic biology has gone through a similar revolution from Linnean to Cladistic. Does it solve all the species/evolution complications? No. But it simplifies they many that remain. As I wrote in The Arts of Truth, Veritas is elusive and in most cases unapproachable. But we can do better or worse in the approach. You post a classic example.
Ristvan,
There is little confusion about what constitutes a mammal. To lumpers such as myself, any amniote with the mammalian jaw joint is a mammal. Splitters might consider those with both the mammalian and “reptilian” (also amphibian and fish) jaw joint is mammiliformes or a proto-mammal, like Morganucodon.
All living mammals, indeed since the Triassic or Early Jurassic, have just the mammalian joint, so there is only a small number of Triassic forms which could go either way. The discovery of Morganucodon and its ilk came as a shock to creationists, BTW. Students are also sometimes surprised to learn that the key distinguishing derived trait shared by all mammals is the jaw joint, not hair or milk. Luckily for paleontologists, the jaw joint fossilizes well.
But the main point is that modern cladistic, phylogenetic taxonomy is not hierarchical. It’s based upon shared, derived traits and genetic similarity, not any imagined hierarchy. It’s bushy, not hierarchical.
The problem with celestial bodies is that classifying them doesn’t have the benefit of evolution, so astronomy is stuck with a system more akin to the Linnaean, based on “anatomical” similarities.
I should add that even in ostensible “mammiliformes” like Morganucodon, the vestigial “reptilian” jaw joint has already been coopted for hearing, while the mammalian joint is the main bite force connection. Its former jaw bones are well on their way to becoming the little bones of the mammalian middle ear.
jeez
https://en.wikipedia.org/wiki/Natural_kind
Mother very easily made a jam sandwich using no peanuts. An obscure reference, I left off the mayonnaise and glue part, but it fits. Now, who groks the reference?
Severian @ur momisugly 10:43
Thanks to the IAU…Many Very Eminent Men Just Stuffed Up Numerous Planetariums!
They have a lot to answer for!
Pluto never stopped being a planet to me. Like we needed a self defined group of “scientismists” to guide the ignorant masses about the razor thin dividing line between planet and unplanet.
9th planet…. was, is, and always will be.
(as will starFISH remain a fish, Arabic numerals are Arabic, guinea pigs remain pigs) etc
How can they be Arabic numerals if the Arabs don’t use them?
The problem is that soon there will be dozens, then hundreds, then thousands or more of “Plutos”. When there are 10,000 planets, what’s the point?
“I want the public to fall in love with planetary exploration as I have,” Runyon said. “It drives home the point of continued exploration.”
Getting to the heart of the matter: Continued exploration = continued funding.
For some trivia, go here:
https://en.wikipedia.org/wiki/NASA#/media/File:NASA-Budget-Federal.svg
Note what happened after October 1957, after Sputnik happened (what happened after Sputnik happened is NASA happened.)
The glory days of NASA went from 1958 (its creation) to, say 1966, its peak funding as measured as a portion of GDP; It has been tough for NASA ever since.
A correction: The chart does not show NASA’s funding as a portion of GDP, instead it shows NASA’s budget as a portion of Federal funding.
Can’t make Pluto a planet without also making the larger Eris into a planet. Eris has a moon too, maybe more. Once you’ve done that, then the question is where you draw the line between them and the smaller round planetoids. It obviously makes most sense to draw that line on this side of Eris, so leaving things as they are. But it’s educational to discuss the topic once in a while.
IMO the IAU did the right thing. There are other Trans-Neptunian Objects bigger than Pluto, too, and more will be found. Limping them in with spherical objects like Ceres but excluding them from planetary status makes perfect sense.
Pluto is significantly smaller than Mercury, but more importantly much less massive. It’s basically a big comet, composed of ice and rock rather than rock and metal, like Mercury, which resembles a planetary core. As I said, it would not have been rated a planet in 1930 had its true size and mass been known, any more than the largest asteroid belt object Ceres was considered a planet.
No the IAU did not do the right thing. See my comment later on in this thread and Pluto is not a comet. See the definition of comet.
Regards
Climate Heretic
I never said that Pluto was a comet. I said it had characteristics of both comets and planets, but is clearly not a planet by any rational definition. It would not ever have been considered one if discovered in 1980, when its true size could have been seen
Its eccentricity is extreme, as I also commented, about 15 times greater than earth’s.
This effort was so ridiculous that it does not benefit from your poking more fun at it. Sorry, I know in my little mind there are nine planets. My elementary school papier mache models said so. And I stand by them.
The problem is that someone thinks there needs to be a definition based on criteria. If the IAU had sense the definition of a planet would just be – one of the 9 we all know as planets- end of discussion. If that seems arbitrary one can add the caveat “for historical reasons.” Is anyone proposing that we rename the Sun because it’s been discovered to actually be a star? No, for interesting historical reasons the Sun is called the Sun and the stars are something different. This is a good thing because it means that every budding scientist sometime early in their education goes through a realization or about the true nature of the Sun. The other problem of course is that the debate has become whether to call Pluto a planet or something else – not well specified. Since there is no really well know alternative to the term “planet” that has caught on, people have started calling Pluto a “minor planet” or a “dwarf planet.” Doing this wins the debate for the “Pluto is a planet” crowd because of the way adjectives work. A minor planet is a planet just as much as a giant planet is a planet. And a dwarf human is certainly a human despite the “dwarf” adjective.
The definition of dwarf or minor planet is straightforward. It’s massive enough to form a sphere, but hasn’t swept other large objects out of its orbit.
The planets now recognized as such aren’t just for historical reasons. We now have exoplanets to consider, so an agreed upon definition is required. Science needs precise definitions.
Exoplanet, minor planet, giant planet, gas planet, secondary planet, protoplanet, traditional planet, : Use any prefix or adjective you like with the word “planet” and what you have is a planet. For now *our* planets are the ones we all learned in elementary school and that were given the names of classical pagan gods. When there are new discoveries it can be decided what kind names to give them. I’m not even sure I want to call any of the traditional planets merely a planet. Mars is mars. Coincidentally it’s something that roughly fits in with the notion of a planet. Although it is quite different from the rest of them. It’s these differences that makes them worth knowing about, so I’m not sure what the need for precision is if it’s the differences in them that make them unique and interesting. Mars does wander across the sky though – in the way that stars don’t. This I think, is the original and best starting point for the definition of a planet. If the word seems imprecise just substitute “satellite” with appropriate modifiers. Hmmm on the other hand maybe we should take a cue from Prince ….How about just, ♇ formerly known as Pluto.
Good points HankHenry
Regards
Climate Heretic
If Pluto be a planet, in the future there will be hundreds, then thousands of “planets”.