"I am a planet, not minor-planet designation 134340"
October 2, 2014 6:10 AM   Subscribe

Is the epically orbiting Pluto, the only planet to be named by a female, about to be reinstated its first class status asks the Independent, eight years after the International Astronomical Union controversially downgraded it to dwarf or minor planet. Since this move, more moons have been discovered and the case for righting this alleged planetary prejudice has continued to be made. While some headlines of today misleading claim that its planetary status has been restored, the public vote has so far been in favor. Scientists have debated, but questions remain over whether returning planetary citizenship to Pluto would also mean having to greencard the larger Eris, Ceres or other bodies in our solar system.
posted by Wordshore (122 comments total) 19 users marked this as a favorite
 
When Pluto was demoted, the argument made a lot of sense to me — a complete layman. I have yet to read any argument in favour of reinstating 'planet' status that goes beyond "I learned it in school" (as though nothing ever changes) and / or some ridiculous anthropomorphic attachment to the "underdog planet."

Officially call it "floating space rock," and it doesn't become less interesting, nor does it devalue the accomplishment of its discoverer.

Ultimately, it's most disappointing that the bulk of the discussion about Pluto has been regarding it's descriptor — not the scientific pursuits related to studying the object. Argh.
posted by Dark Messiah at 6:16 AM on October 2, 2014 [19 favorites]


This debate is one of the best popularizations of an ancient philosophical problem ever. Somehow we found a version of "heap"-vs-"not-a-heap" which entails a ton of emotional attachment (so it captivates many people) but no questions of morality (so the ensuing disagreement doesn't infuriate most people).
posted by roystgnr at 6:29 AM on October 2, 2014 [21 favorites]


Just make Eris and Ceres special districts or territories with oversight by all of the other elected planets or with an elected but non-voting representative planet.
posted by Buttons Bellbottom at 6:29 AM on October 2, 2014 [26 favorites]


E&C instead of DC?
posted by edgeways at 6:33 AM on October 2, 2014


"Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Haumea, Makemake, Eris." If I had to memorize nine planet, kids today can learn to Google thirteen.
posted by dances with hamsters at 6:35 AM on October 2, 2014 [5 favorites]


They're restoring its status preparatory to announcing the true nature of Charon; unfortunately, Cerberus is already there...
posted by Halloween Jack at 6:38 AM on October 2, 2014 [2 favorites]


I vaguely remember seeing some movie set in the U.K. where one of the plot lines was that the town was proud of it's mountain but a government surveyor came through and told that it wasn't actually tall enough and had been re-designated as a hill. So, the town undertook a massive effort to cart dirt up their hill and piled it on top so that they could have the surveyor measure it again when he came back through. I think that, while everyone was upset because their town's mountain had always been a mountain, they also understood that if they kept calling it a mountain, all these other hills would have to become mountains too.

If people want Pluto to be a planet, then they should undertake a mission to gather up some wayward asteroids or something and pile them on Pluto until Pluto is big enough to be a planet, is what I'm saying.
posted by VTX at 6:39 AM on October 2, 2014 [35 favorites]


I think you're making this whole controversy up. emergent.info has nothing about this.
posted by cjorgensen at 6:39 AM on October 2, 2014 [1 favorite]


The whole concept of the IAU having a vote about what officially counts as a planet, with the expectation that the result will be widely obeyed, is so very silly. It's like APSA having a vote about what officially counts as a political party or MLA having a vote about what officially counts as a novel, with the expectation that all schools everywhere will shuffle their curricula to accommodate it.

More to the point: I can't imagine any scientific research that becomes possible by having an official IAU definition of a planet that was impossible without it, though of course not being in astronomy I could be wrong. So what's the point?
posted by ROU_Xenophobe at 6:40 AM on October 2, 2014


I vaguely remember seeing some movie set in the U.K....


I think you're thinking of The Englishman Who Went Up A Hill But Came Down A Mountain.
posted by DiscountDeity at 6:42 AM on October 2, 2014 [4 favorites]


As someone who has watched a lot of Sailor Moon, I strongly feel that Pluto should be reinstated, because otherwise who is guarding the Door of Space-Time?!!?!?
posted by maryr at 6:44 AM on October 2, 2014 [13 favorites]


The Earthican Who Visited A Minor Planet But Came Back With A Huge Frozen Orb Heading Toward Us Even Now.
posted by The Whelk at 6:45 AM on October 2, 2014 [10 favorites]


Call Pluto a planet again, and take advantage of the publicity to also usher Ceres, Eris, Hauemea, Makemake, Sedna, and any of the other extremely fascinating worlds still being found officially into the planet club. (And I agree that we need to fix the omission of thousands of exoplanets from the official definition!) Kids learning that new worlds *are being discovered every day* is a feature, not a bug.

I mean, you can still call the smallest class of worlds "dwarf planets". We also have "giant planets" (Jupiter, Saturn), "ice giants" (Uranus, Neptune), and "terrestrial planets" (Mercury, Venus, Earth, Mars). They're very different from each other. They're all planets. Somehow everyone deals with that knowledge just fine.

... plus if we do this soon, then next year there will be two missions to planets we have never visited before...
posted by puffyn at 6:48 AM on October 2, 2014 [19 favorites]


I wish they'd stop asking the public about this. It's like asking "Do you think Foxes should be a kind of dog, or a kind of cat?" Shouldn't matter what the public thinks.

Either there are eight planets in this system, or there are thousands. Thirteen makes no sense at all, because all you have to do is keep looking to find yet another little ball beyond Neptune.
posted by General Tonic at 6:49 AM on October 2, 2014 [13 favorites]


Right, my point is: why do there have to be a fixed number of planets at all? Do we only have nine countries, because otherwise little kids would have to memorize hundreds?
posted by puffyn at 6:50 AM on October 2, 2014 [3 favorites]


Forget descriptors - - the real photos are almost here!

The New Horizons spacecraft is only 284 days out from Pluto now, after it's nine year mission to get there.

It's hard for me to express just how exciting this is for a lifelong "planet" watcher like myself!
posted by fairmettle at 6:51 AM on October 2, 2014 [13 favorites]


The reason we no longer consider Pluto a planet like the other 8 is due to its wildly eccentric orbit. The "major" planets all seem to have formed at the same time and in the same way, due to the fact that they all orbit the Sun in a nearly flat circle (which we refer to as the "ecliptic plane" because that's what causes eclipses).

Pluto's orbit, by comparison, is nothing like the other planets, exhibiting characteristics similar to a caught asteroid. While Pluto may "wander" around the sun like the other planets (planet, in fact, simply means "wanderer"), we no longer think it falls under the same classification as the major planets. We actually have a spacecraft called New Horizons on its way to Pluto, due to arrive in Summer 2015, that will hopefully tell us more about the enigma that is our Sun's ninth satellite.
posted by johnnyace at 6:53 AM on October 2, 2014 [6 favorites]


(Foxes are dogs, they are in family Canidae.)
posted by maryr at 6:53 AM on October 2, 2014 [2 favorites]


because all you have to do is keep looking to find yet another little ball beyond Neptune.

Behind which comes a running child, so be careful driving your spaceship.
posted by bondcliff at 6:55 AM on October 2, 2014 [6 favorites]


I think you're thinking of The Englishman Who Went Up A Hill But Came Down A Mountain.

...starring Dr House, Stannis Baratheon's wife, Winston Churchill (Dr Who version) and Chief O'Brien!
posted by Major Clanger at 7:00 AM on October 2, 2014 [3 favorites]


(Foxes are dogs, they are in family Canidae.)

That's not what I learned in school! Foxes should be cats, and I have a Facebook page with 800,000 Likes to prove it!
posted by graphnerd at 7:12 AM on October 2, 2014 [10 favorites]


If the Moon was massive enough for the center of the Earth-Moon orbit to be above the surface of the Earth*, would it be considered a planet in a dual-planet system?

(*The actual barycenter is apparently about 74% of the Earth's radius from the center of the Earth.)
posted by George_Spiggott at 7:12 AM on October 2, 2014


The reason we no longer consider Pluto a planet like the other 8 is due to its wildly eccentric orbit.

Actually, what that plot really shows is Pluto's wildly inclined orbit. Mercury is almost as eccentric as Pluto (e=0.20 vs. e=0.25).

But if high eccentricity or inclination were a problem, somebody should really tell the exoplanets. (Most of the planets in our solar system have unusually circular and flat orbits compared to the planets we've found around other stars.)
posted by puffyn at 7:12 AM on October 2, 2014 [5 favorites]


(To answer my own question, apparently when Pluto was considered a planet, Pluto-Charon was considered a double planet for this very reason, because the common center of gravity is between them rather than within Pluto.)
posted by George_Spiggott at 7:15 AM on October 2, 2014


(Foxes are dogs, they are in family Canidae.)

This is an important question. There is now a survey.
posted by Wordshore at 7:18 AM on October 2, 2014 [5 favorites]


Right, my point is: why do there have to be a fixed number of planets at all? Do we only have nine countries, because otherwise little kids would have to memorize hundreds?


I think it's a vestige of the longstanding identification (both pagan and Christian) of the skies with a theological heaven or seat of the divine. Re-classification of celestial bodies suggests the possibility of change in things that oughtn't be able to change. I don't mean at a theological or philosophical level, I mean at a semiotic level: re-classification challenges and opens up the meaning of the heavens.

I don't think any of this is at a conscious level in most people. There is bound to be anxiety whenever there is a big shift in the meaning of something, particularly if the something is semantically adjacent to, or includes within it, the very concept of being fixed and unchanging.
posted by gauche at 7:21 AM on October 2, 2014 [9 favorites]


The reason we no longer consider Pluto a planet like the other 8 is due to its wildly eccentric orbit

That's like saying Gary Busey isn't a human.

I'M SICK OF THIS SHIT. If it's in orbit around the sun it's a fucking planet mmmkaaay?
posted by jimmythefish at 7:22 AM on October 2, 2014


The reason we no longer consider Pluto a planet like the other 8 is due to its wildly eccentric orbit.

The IAU definition says "A planet is 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." (link)

Pluto was downgraded to "dwarf planet" because (a) and (b) applies, but not (c).
posted by effbot at 7:23 AM on October 2, 2014 [1 favorite]


That's like saying Gary Busey isn't a human.

I'm OK with the IAU looking into that. More research is clearly needed.
posted by PlusDistance at 7:25 AM on October 2, 2014 [8 favorites]


The IAU definition says "A planet is 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." (link)

Pluto was downgraded to "dwarf planet" because (a) and (b) applies, but not (c).


The trouble is, that would also exclude Neptune because it has failed to clear Pluto from its neighborhood. A quibble--I know--but, uh, science?

Did they forget to include (d) is bigger than Pluto?
posted by General Tonic at 7:31 AM on October 2, 2014 [1 favorite]


I'm OK with the IAU looking into that. More research is clearly needed.

Does winning Celebrity Big Brother qualify as clearing your neighbourhood? You have to get everyone else evicted to win, right?
posted by effbot at 7:41 AM on October 2, 2014 [1 favorite]


If I had to memorize nine planet, kids today can learn to Google thirteen.

"My Very Excellent Mother Certainly Just Sent Us Nine Perfectly Honed Mobius Eclairs"
posted by ubiquity at 7:43 AM on October 2, 2014 [8 favorites]


The reason we no longer consider Pluto a planet like the other 8 is due to its wildly eccentric orbit

When I think of science facts that amaze me, I think a big one is that Pluto can even have an orbit around a sun that is 3.67 billion miles away. It takes light from the sun about 5 hours to get there. Gravity is cool.
posted by SpacemanStix at 7:45 AM on October 2, 2014 [2 favorites]


The 'cleared its neighborhood' thing is pretty damn arbitrary. There's no scientific definition of what constitutes 'clear.' Is Earth not a planet because there are still near-Earth asteroids? There are a fuckton of variously sized hunks of rock/ice/metal whizzing around the sun and no planet's orbit is really ever going to be truly 100% 'clear.'
posted by rbellon at 7:46 AM on October 2, 2014 [1 favorite]


That's like saying Gary Busey isn't a human.

I'M SICK OF THIS SHIT. If it's in orbit around the sun it's a fucking planet mmmkaaay?


What if Gary Busey had himself launched into a stable solar orbit, Gen. Treister-style? Would that make him a planet?
posted by Strange Interlude at 7:49 AM on October 2, 2014 [1 favorite]


The trouble is, that would also exclude Neptune because it has failed to clear Pluto from its neighborhood. A quibble--I know--but, uh, science?

Not to mention the smattering of Trojan asteroids sharing (relatively) stable orbits with Jupiter, Mars, and Earth. "Clear" doesn't really help that much and could probably be replaced with something like, "has captured more than x% of the mass in its orbit."

I suspect this debate is going to flip/flop multiple times depending on whether you emphasize internal structure (assuming that dwarf planets have geologic processes analogous to to the rocky ones) or orbital mechanics (dwarf planets have negligible effects on the orbits of neighboring bodies).
posted by CBrachyrhynchos at 7:49 AM on October 2, 2014 [1 favorite]


I wish they'd stop asking the public about this.

Exactly. We already have a governing body that makes scientific decisions on what it thinks the public wants - it's called Congress, and look how well that turns out.

Definitions are extremely important in science- you can have controversy around the definitions, that's part of the process, but making decisions to exclude or include specific things due to sentiment and not definition is not good science. Pluto either is or isn't a planet, and if it is then other planets needs to be included, and if it isn't then you need to apply those exclusionary rules to other planet like things as well. This is what makes the public not trust science.
posted by barchan at 7:52 AM on October 2, 2014 [1 favorite]


foxes are procyonidae.
posted by bruce at 7:54 AM on October 2, 2014


Today I learned that our solar system has 13 planets, but the IAU is glossing over that. The hell?!
posted by Brandon Blatcher at 7:56 AM on October 2, 2014


shouldn't we start breaking away from the naming of planets after Greek cultural figures? I mean, sooner or later that pantheon will be used up.
posted by angrycat at 7:56 AM on October 2, 2014


Well, it is very Romanist.
posted by Brandon Blatcher at 7:58 AM on October 2, 2014


I've always thought a better description of planet would be that an object appears to have been the 'primary accretor' at its orbital distance during formation of a solar system. So the classic eight planets would count, because they all appear to have formed that way, but asteroid belt objects (like Ceres) and Kuiper belt objects (like Pluto) would be right out. Because ultimately, they're not really primary accretors, but more the stuff left over when a primary accretor doesn't form at that distance from the sun.

I think that gives a better reason for the difference in definition (since it represents an important developmental difference) and encompasses what they're really going for with their 'clearing the neighborhood' definition.
posted by Mitrovarr at 7:58 AM on October 2, 2014 [1 favorite]


or are they Roman names shit oh well I always confuse those two
posted by angrycat at 7:58 AM on October 2, 2014


As someone who has watched a lot of Sailor Moon, I strongly feel that Pluto should be reinstated, because otherwise who is guarding the Door of Space-Time?!!?!?

It's still her, but she is now officially recognized as a Dwarf Sailor.
posted by Wolfdog at 7:59 AM on October 2, 2014 [3 favorites]


It's still her, but she is now officially recognized as a Dwarf Sailor.

Aye, that's Handsome Pete. He dances for nickels!
posted by Strange Interlude at 8:04 AM on October 2, 2014 [1 favorite]


Here's the Wikipedia article on the "clearing the neighborhood" definition. It very much seems like specious bullshit that isn't very clear.
posted by Brandon Blatcher at 8:05 AM on October 2, 2014


shouldn't we start breaking away from the naming of planets after Greek cultural figures?

Already done. Haumea is named after a Hawaiian goddess of fertility.
posted by General Tonic at 8:06 AM on October 2, 2014 [1 favorite]


shouldn't we start breaking away from the naming of planets after Greek cultural figures? I mean, sooner or later that pantheon will be used up.

They've long since started using other mythologies including Inuit and Polynesian.
posted by George_Spiggott at 8:07 AM on October 2, 2014


Pluto is:

1) Significantly different in a number of ways from all the other bodies which are called planets, and

2) Exactly the same in every respect as all the other bodies which are called Kuiper Belt objects.

Giving these two classes of objects two different names is useful because they formed in different ways and behave in different ways.

Why this is at all controversial continues to elude me.
posted by kyrademon at 8:07 AM on October 2, 2014 [16 favorites]


Oh, and the moons of Uranus are named for magical characters in English literature, mainly Shakespeare.
posted by George_Spiggott at 8:11 AM on October 2, 2014


It's still her, but she is now officially recognized as a Dwarf Sailor.

Pretty sure Chibiusa has that more than covered.

Also, she is the worst.
posted by maryr at 8:14 AM on October 2, 2014


Look, if we keep this debate up, eventually they are going to have to address the problem of Yuggoth, and that is not going to end well. Leave Pluto alone, it's not so much a planet or a non-planet as a mask.
posted by GenjiandProust at 8:15 AM on October 2, 2014 [3 favorites]


Today I learned that our solar system has 13 planets, but the IAU is glossing over that. The hell?!

Thanks, Obama.
posted by Wordshore at 8:15 AM on October 2, 2014 [1 favorite]


Now there's even a dwarf planet candidate named after a character from Tolkein.
posted by Mitrovarr at 8:19 AM on October 2, 2014 [1 favorite]


[blink]Survey update[/blink]

MetaFilter currently undecided on whether foxes are cats or dogs.
posted by Wordshore at 8:26 AM on October 2, 2014


Definitions are extremely important in science

Within a specific project, yeah, but less so in a more general sense. In the world I work in, it's important to specify exactly what definition of "the south" you're using -- the ex-confederate states, the Census south, CSA+OK+KY, or others. In the same way that kyrademon notes, all of these definitions hinge on patterns of self-similarity and differences from others, but exactly which makes the most sense to apply will depend on which patterns are relevant for your research.

Having anyone -- the Association of American Geographers, the Census Bureau, the American Sociological Association, etc -- vote on the one and only definition of the south would be deeply silly, irrespective of whatever they actually decide. In the same way, having a big vote on whether Pluto is a planet is silly whether they decide it is or it isn't.

Pluto either is or isn't a planet

It's entirely possible that perfectly good science might treat it as a planet for some purposes or some research projects and not for other purposes or research projects, in much the same way that carbon can be a heavy metal or nonmetallic depending on what your research project is.
posted by ROU_Xenophobe at 8:39 AM on October 2, 2014 [1 favorite]


I say we just recategorize Pluto every few years so we can teach kids the difference between taxonomy and empiricism.
posted by Wemmick at 8:45 AM on October 2, 2014 [14 favorites]


How I Killed Pluto and Why It Had It Coming is short yet a little over-long - a little chatty for the subject matter - but did a good job of summarizing the history and the arguments that got us to where we are.

The IAU came up with a ridiculous, elaborate, arbitrary technical definition of "planet" that was designed to exclude Pluto-like bodies, which is kind of perverse. "Planet," in the "wandering star" sense, is a very old word, a very old idea. One which has served well enough for hundreds of years of serious astronomy without an elaborate technical definition. Turning it into highly technical jargon can obviously cause some confusion, but for what upside? Pluto, Ceres et al. don't care what you call them.

There was apparently a proposal at one of the IAU congresses to just admit that the "planetary" status of the traditional nine really was arbitrary, a matter of history and tradition, rather than a matter of any formal or important taxonomy, and to just recognize that tradition and make it official. "These nine are planets and the zillion bitty new ones we inevitably will find are not." That sure sounds like a simple, sensible answer.
posted by Western Infidels at 8:48 AM on October 2, 2014 [4 favorites]


Pluto either is or isn't a planet
It's entirely possible that perfectly good science might treat it as a planet for some purposes or some research projects and not for other purposes or research projects, in much the same way that carbon can be a heavy metal or nonmetallic depending on what your research project is.
Schrödinger's Planet?
posted by Buttons Bellbottom at 8:49 AM on October 2, 2014 [1 favorite]


I have no idea if the explanation is correct, but here's an explanation of why Neptune "clears its neighborhood": https://answers.yahoo.com/question/index?qid=20060825064918AAh4ji7
posted by 23skidoo at 8:50 AM on October 2, 2014


"My Very Excellent Mother Certainly Just Sent Us Nine Perfectly Honed Mobius Eclairs"

Great! Now extend it to include the following:

Orcus
Ixion
Salacia
Varuna
Quaoar
Sedna

And you also want to add in the following:

2002 MS4
2005 UQ513
2007 OR10
2007 UK126

Finally, you'll probably want to set that dirty up so you can expand it to include a hundred or so extra planets, once the outer system searches really get going.

(Incidentally, I really like the "central point of accretion" definition.)
posted by happyroach at 8:50 AM on October 2, 2014


the only planet to be named by a female
by a female what?
posted by ziggly at 8:52 AM on October 2, 2014 [5 favorites]


Secret Planets They Don't Want You To Know About: The Hidden Truth
posted by double block and bleed at 8:58 AM on October 2, 2014


I'M SICK OF THIS SHIT. If it's in orbit around the sun it's a fucking planet mmmkaaay?

"I orbit the sun, Greg, could you milk me call me a planet?"
posted by Celsius1414 at 8:59 AM on October 2, 2014 [3 favorites]


It's a planet because it was accepted as a planet when it was discovered. Large asteroids had already been discovered before Pluto and nobody called them planets. If an orbiting object required technology beyond what was available when Pluto was discovered, it's not a planet. If it was a planet, it would have already been discovered. Pluto was discovered due to orbital resonance and that is more important than whether it cleared it's orbit (which is also a resonance effect). If it's such a tiny speck of dirt that it doesn't have any measurable effect on any other planets, it's not a planet. If that were true, given sufficiently advanced technology, you could measure the gravitational effect of my body on the Earth, which would make me a planet.

I don't really care if astronomers want to argue if it's a planet, a plutino, a cubewano, or how many Plutos can dance on the head of a pin (given a sufficiently large pin). My biggest current planetary designation problem is that my astrology software recognizes Chiron (a/k/a Comet P95) as a planet and this is not optional, it can't be turned off. Lately there is a huge effort to systematize the astrological influence of Centaurs, TNOs and large asteroids, although an astrologer friend (who is the foremost expert in the field of interpreting these small objects) calls them "gravel."

I used to scoff at astrologers who wanted to interpret small bodies like Haumea and Makemake. First of all, why would we interpret the influence of an object based on an arbitrarily chosen mythological name? And why the hell are we using obscure, even extinct mythological systems? Did we run out of Greco-Roman mythology already? The universal answer I got was that planets and other objects get the names they need, it just works out that way. Okay.. well then, if you want to convince me that we should incorporate this "gravel" into astrology, first you'll have to show me how to interpret orbital patterns of moons of other planets, like for example Ganymede, which is larger than Mercury. Unfortunately, I discovered a systematic mathematical approach to this problem, although the interpretation still needs to be addressed. I figure we should probably interpret Jupiter's moons as known to Gallileo before attempting to interpret objects like Eris that were only discovered in the 1970s.

If we're going to start interpreting named objects, I can work with that. I recently found out that there is an asteroid that bears my family name, it is apparently named after a distant relative who is a prominent astronomer. I can easily interpret this. Currently the asteroid is at 24 Sagittarius, and soon will be conjunct Pluto. The interpretation is obvious: the world faces imminent destruction unless there is a global effort to send me vast amounts of money.
posted by charlie don't surf at 9:13 AM on October 2, 2014 [4 favorites]


MetaFilter currently undecided on whether foxes are cats or dogs.
posted by Wordshore at 11:26 AM on October 2 [+] [!]


To be honest, I answered "Dog" (because I know that maryr is a scientist), and the after-voting page had a picture of an extremely cute puppy. So I went back to see if I could get a kitty if I voted "Cat". I didn't. I thought I'd give it one more chance, and see what a stock image of a plate of beans looked like, but instead it showed me human beings, not beans. So you should probably subtract out those last two votes.
posted by benito.strauss at 9:13 AM on October 2, 2014


>> the only planet to be named by a female
> by a female what?


I had the same reaction, and for a brief moment of hope I thought it might have been the only planet discovered by a horse, and that was so cool.
posted by benito.strauss at 9:18 AM on October 2, 2014 [1 favorite]


the only planet to be named by a female
by a female what?


Point of accretion, obvs
posted by Ray Walston, Luck Dragon at 9:18 AM on October 2, 2014


I feel very strongly that the current definition of a planet was selected primarily due to convenience:

Pluto, and the other KBOs like Eris, Sedna -- and surely many others we will find -- are qualitatively different from many of the other planets. In their more eccentric elliptical orbits and in their orbital inclinations to the ecliptic plane.

The IAU was presented with a conundrum: many astronomers considered these differences to be sufficient to NOT include these new bodies in the list of planets. However, the specific criterion selected to exclude Pluto and shove it into the "Dwarf Planet" category is one that a major planet also fails: Neptune.

Neptune is in a 2:3 resonance with Pluto. If Pluto has therefore not been able to "clear its orbital neighborhood" due to the presence of Neptune, Neptune has failed for the exact same reason.

Ultimately, I find it interesting that most people who don't mind Pluto's demotion consider opposution to it to be purely rooted in nostalgia. That may be the case for many, but for me (I have a B.S. In Astrophysics from UCLA for reference, so I have the training to speak with at least some legitimate authority on the issue), I consider the NEW rules to be rooted in nostalgia.

What it comes down to is, should we include Pluto, we would have to expand the list -- there may be dozens of such bodies orbiting the Sun, and proponents of KBOs as separate objects are deeply attached to "not having too long of a list." That's about as un-scientific as it gets.

The IAU current definition specifically does not account for exoplanets -- of which we know of over a thousand, and soon will know many thousands. Furthermore, it does not account for bodies that do not orbit stars, but float freely in interstellar space.

Science is predicated upon simple, physical definitions. A simple, physical definition of a planet was proposed at the IAU but at the last minute -- on the last day of the conference -- the definition was changed before being put up to a vote.

What I consider to be the best definition of a planet is this:
A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet.
I consider this item incomplete, but would merely add two items: 1) that the body may be floating freely and not in orbit around any star or other object, and 2) to clarify that by star we mean conducting nuclear fusion or be a post-main sequence remnant of a body that conducted nuclear fusion (white dwarfs).

The definition as initially proposed has very simple and unambiguous definition. Is it round? Does it orbit a star or float freely? If yes to both, it is a planet.

Every other definition is rooted in resistance to include something that someone doesn't like. Astronomer A doesn't want to call something in the asteroid belt a planet (Ceres), so that pet exclusion gets added in, something like "biggest item in local population" or "cleared its orbital neighborhood," or they don't want to keep updating their lists as we know more information (isn't that the very thing that science is made of?), so out comes "low-eccentricity orbits" and "orbits on the star's ecliptic plane."

But for those ad hoc exclusions for people's pet frustrations, we will find exoplanets that humble and downright humiliate any complicated criteria for definition.

Keep it simple.

1. Is it round?
2. Does it orbit a star, or float freely?

If yes, you have a planet. Pluto, Sedna, Eris, Makemake, and many more. The solar system -- and the universe -- is big enough for plenty of planets.
posted by chimaera at 9:28 AM on October 2, 2014 [8 favorites]


If we already have Orcus, then Demogorgon, Tiamat, Lolth, Takhisis, Juiblex, Great Wyrm Dragon, Cthulhu, Hastur, Grabthar, Loki, Xenu, That One Fighter Todd Had Who Rolled Real Well, FSM, Ra, Gozer, R'hllor, Tori Amos, Helm, Jebus, and other assorted deities should all be considered as well.

I am now going to dedicate my 4 year old son's life to becoming a Sepp Blatter-style corrupt dictator of the IAU so that, after I am gone, he can be sure that there is a planet named after my one true god, Sleeping In On Sundays.
posted by robocop is bleeding at 9:28 AM on October 2, 2014 [1 favorite]


charlie don't surf: It's a planet because it was accepted as a planet when it was discovered. Large asteroids had already been discovered before Pluto and nobody called them planets.

Ceres (and a couple of other large asteroids) were absolutely considered planets when they were discovered, and remained that way for decades. They were demoted later when it became clear that the asteroid belt was full of objects that made a smooth continuum of sizes from Ceres-sized (which is pretty small; Ceres is way smaller than the Moon, for instance) to tiny.
posted by Mitrovarr at 9:33 AM on October 2, 2014 [4 favorites]


Many Verbal Etheral Memes Come Just So U Nab Perfect Harmonious Melodies Essentially Oscillating In Some Varied QuarterS.
posted by Buttons Bellbottom at 9:45 AM on October 2, 2014


Neptune is in a 2:3 resonance with Pluto. If Pluto has therefore not been able to "clear its orbital neighborhood" due to the presence of Neptune, Neptune has failed for the exact same reason.

For all its faults, the idea of "clearing its orbit" is not quite this bad. Every planet has objects in resonances (except maybe Mercury), including the Earth. Jupiter's Trojans are probably the most well known. There is clearly no intention of requiring planets to clear objects out of its own resonances, it would make no sense.
posted by kiltedtaco at 9:51 AM on October 2, 2014 [2 favorites]


Luna is pretty damn big, all things considered, so I'm not sure using it as hte "You must be this tall..." standard means anything.


"Is it round?" is actually a pretty good standard for rocky objects, but for anything icy that gets close enough to the sun to get mushy...I mean, yeah, I'm carrying a few extra pounds buy I don't think there should be any chance that I outweigh a full fledged planet.
posted by Kid Charlemagne at 9:52 AM on October 2, 2014


This has nothing to do with science. This is about HUMANITY.

Pluto is a lonely potato and a microscope and a Roomba and a crouton.

It's okay, little guy. You haven't done anything wrong. Nothing!! I love you just the same as I always have, and I would never want to make you sad. You will ALWAYS be a planet to me, no matter what some people try to say about you. ALWAYS. AND FOREVER.

Sniff.
posted by argonauta at 9:54 AM on October 2, 2014 [1 favorite]


Here's a reasonable classification for our solar system:

Major Planet: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
Dwarf Planet: Ceres, Pluto, (Charon?), Eris, and other wee-but-spherical bodies
Minor Planet: asteroids, comets, etc.

All "planets" of various kinds, with qualifiers for the subclasses. (Extra-solar planets are just unqualified "planets" since we can't determine their shape.)

What the IAU did, however, was to say two contradictory things:
  1. A planet is round, orbits a star, and has cleared its neighborhood.
  2. A dwarf planet is round and orbits a star, but hasn't cleared its neighborhood.
This means that "dwarf planets" are not "planets", which is goofy. This is what you get when you draft and redraft proposals about a controversial subject in a huge hurry with a deadline.
posted by The Tensor at 9:56 AM on October 2, 2014 [1 favorite]


'Is it round" is actually quite tricky, because there's a whole class of objects (spanning the lower end of dwarf planet and the upper end of asteroid/KBO/SDO) that are big enough to be 'round-ish' but not totally spherical (well, as spherical as a major planet). Plus you have things that are not round, which are more massive than other things that are round.

Some objects are big enough to become spherical if molten but not if they aren't, so they're spherical if they've never been disrupted but not spherical if they have been and reformed. Vesta is a good example of this. Rotation can also spin things into rather odd shapes - Haumea is a potential dwarf planet spun into an ellipsoidal shape.
posted by Mitrovarr at 10:04 AM on October 2, 2014 [3 favorites]


My biggest current planetary designation problem is that my astrology software...

Damning scientific taxonomy because it screws up your astrological system. This is a wonderful bit of satire, right?
posted by one_bean at 10:26 AM on October 2, 2014


All of these designations are going to get really confusing once the monoliths convert Jupiter into Lucifer.
posted by ckape at 10:26 AM on October 2, 2014


Large asteroids had already been discovered before Pluto and nobody called them planets.

Pallas and Ceres were both declared as planets when they were first discovered. I am fine with our solar system have dozens of planets or having eight. I think the other numbers are silly. (Pluto sized or larger and discovered before 1950 seems pretty arbitrary, and is what the classification comes down to if you want 9. If you ignore the 1950, why Pluto sized? If you go with round due to internal gravity, you're going to hit dozens.)
posted by Hactar at 10:27 AM on October 2, 2014 [1 favorite]


If we already have Orcus, then Demogorgon, Tiamat, Lolth, Takhisis, Juiblex, Great Wyrm Dragon, Cthulhu, Hastur, Grabthar, Loki, Xenu, That One Fighter Todd Had Who Rolled Real Well, FSM, Ra, Gozer, R'hllor, Tori Amos, Helm, Jebus, and other assorted deities should all be considered as well.

The first unabashedly bogus planet should be called Glycon.
posted by Halloween Jack at 10:30 AM on October 2, 2014


If I had to memorize nine planet, kids today can learn to Google thirteen.

My mom says Pluto is a planet!

My mom says Pluto is a minor planet!

You poked my heart.
posted by obscure simpsons reference at 10:40 AM on October 2, 2014 [2 favorites]


ALL THESE WORLDS
ARE YOURS EXCEPT
PLUTO
WHICH IS NOT REALLY A PLANET, MORE LIKE A KUIPER BELT OBJECT WITH DELUSIONS OF GRANDEUR
YOU COULD ATTEMPT A LANDING THERE, I GUESS
BUT, WHY BOTHER?

posted by Atom Eyes at 10:51 AM on October 2, 2014 [13 favorites]


Pallas and Ceres were both declared as planets when they were first discovered.

Well according to your wikipedia link (LOL) the Sun and Moon, as well as the moons of Jupiter were originally considered planets. Back then, a planet was a "wandering star" that did not have a fixed position against the celestial background, so there was no distinction between types of wandering stars. They didn't even know there were different types.

BTW ckape, the IAU will never ever allow any object in the solar system to be named Vulcan.
posted by charlie don't surf at 10:57 AM on October 2, 2014


In my opinion, the reclassification didn't go far enough. Any reasonable cladistics would not only split Dwarf Planets into their own category, but the Gassy Giants as well. But splitting the classical planets would likely be a political non-starter.
posted by CBrachyrhynchos at 11:11 AM on October 2, 2014


Am I the only person having images of planets that look like Peter Dinklage?
posted by Brandon Blatcher at 11:14 AM on October 2, 2014


Vulcan is a pretty terrible name for a moon of Pluto. Even if you swap around the Greek/Roman counterparts I don't think those two ever hung out in mythology.
posted by ckape at 11:18 AM on October 2, 2014


the omission of thousands of exoplanets from the official definition

They are planets, or at least "planets". They're just someplace else, hence "exo".

They were demoted later

This is a silly way to describe being reclassified.

The arbitrariness here is more of a feature than a bug. Yes, the definition is what it is, but it sort of needs to be. In most ways that matter it's scientifically irrelevant.
posted by dhartung at 11:33 AM on October 2, 2014


Neil deGrasse Tyson is going to be pissed
posted by edgeways at 11:33 AM on October 2, 2014


The sun was no longer classified as a planet in 1857, while the objects orbiting it were grouped into primary planets and secondary planets, which were moons. About a century ago, when they could see more and more of the asteroids due to improvements in telescopes, they stopped calling them planets. The situation with Kupier Belt objects today is analogous.

Pluto even gets it's own classification of planet (Plutinoids), something it shares only with Jupiter (Hot Jupiters) and Earth (Earht-like, Super Earth, etc. for exo-planets). And it's the only one that gets a category for objects in the solar system.

Let it stay dead and buried or resurrect Pallas (and Juno and Vesta and Ceres).

Personally, I like the "spherical from internal forces and orbits the sun" for the definition of a planet. Then you have what I would call, for lack of a better term, the important planets, the ones that actually shape the solar system- the terrestrials, the gas giants and the ice giants. The rest just do their own thing and don't bother anyone else.
posted by Hactar at 11:35 AM on October 2, 2014


I will always know you as 823038... OOOPS! Wrong story.
posted by Perko at 11:39 AM on October 2, 2014


The history of Ceres's classification pretty closely matches that of Pluto. I think I remember hearing that Ceres was also initially called "Planet X", but any googling for that now just gives a bunch of Nibiru nonsense.
posted by ckape at 11:40 AM on October 2, 2014


I would like to see the 2006 IAU meeting re-enacted in a manner similar to Civil War re-enactments.
posted by Brandon Blatcher at 11:43 AM on October 2, 2014 [1 favorite]


What do the MetaFilter public think? It's survey update time!
posted by Wordshore at 11:53 AM on October 2, 2014


Mitrovarr's very interesting Haumea link has initiated me into the mysteries of the Kozai effect, in which an object with an inclined orbit can exchange some of that inclination for eccentricity, developing an orbit which is less inclined but more eccentric (and vice versa), and this process can continue indefinitely, resulting in a periodic oscillation of the object's orbit between points of maximal inclination and maximal eccentricity:
The Kozai Mechanism causes a periodic exchange between the inclination and eccentricity of an orbit.
It has been theorized that the Kozai Mechanism is responsible for the high eccentricities observed in the orbits of exosolar planets. If the parent star has a massive yet unseen substellar companion, orbiting at a great distance, and in an orbit highly inclined to the plane of the planets' orbits, the Kozai Mechanism should induce high eccentricities into the orbits of the planets.

It is also theorized that the Kozai Mechanism may be responsible for the high eccentricities observed in the orbits of many Kuiper Belt Objects such as 2003 UB313. The pull of the Milky Way Galaxy causes an object with a high eccentricity to periodically trade this eccentricity for a gain in inclination.

The Jovian system is influenced by the Kozai Mechanism as well. Although Jupiter has many irregular, distant moons orbiting in a myriad of directions, the Kozai Mechanism has set an upper limit of about 60 degrees on their inclinations. Any moon whose inclination exceeded this value would periodically gain an eccentricity so large that its perijove would take it into the region of the Galilean Moons. Its fate would be a collision with one of the Galilean Moons, a collision with Jupiter, or an ejection from the Jovian system.


Jupiter is surrounded by a large system of irregular moons beyond the orbits of the Galilean Moons (purple). Although these moons possess a wide range of inclinations and eccentricities, polar orbits are non-existant.

If the Earth's Moon were in a circular polar orbit, with the same semi-major axis (distance) that it has now, it would quickly be ejected into interplanetary space, or collide with the Earth.

The simulation kozai.gsim places the Moon in a circular polar orbit around Earth. It orbits at a distance of 384,000 kilometers from the Earth's center. The Moon completes many orbits of the Earth with only minimal effect to its orbit. But these effects grow, and soon the Moon's orbit is very elliptical. After 8 years, the Moon slams into the Earth.

The maximum eccentricity attainable through the Kozai mechanism may be approximated from the formula from Takeda and Rasio's 2005 paper.

Here is a javascript calculator that allows you to try different numbers in their formula: ...
If Pluto's orbit's inclination is continually changing, and the shape of that orbit is shifting at the same time, that would seem to make the task of clearing the orbit more difficult, and certainly at least a longer process.

And now that puffya has clued me in to how eccentric Mercury's orbit is, I'm wondering whether we're seeing it near a point of minimal orbital inclination, and whether in the future it will orbit significantly out of the ecliptic.
posted by jamjam at 12:03 PM on October 2, 2014 [4 favorites]


I have already decided that the first outright lie I will tell my daughter will be this: Pluto is a planet and don't let anyone tell you otherwise.

/parental defiance
posted by lydhre at 12:09 PM on October 2, 2014 [5 favorites]


Which is to say, bring on more planets! Eris and Ceres and any future buddies of planetary size can totally join the club, I don't see why we need to limit ourselves to 8. It's not like the solar system is book club and you're trying to exclude that one weird kid who wants to join and make everyone read The Fountainhead.
posted by lydhre at 12:14 PM on October 2, 2014


"Pluto is not a planet. It's not a planet! I'm an idiot! I love my son!"
posted by yoHighness at 1:26 PM on October 2, 2014 [1 favorite]


It's funny that everyone pays attention to the scientific revisions that bother them, but not the ones that are awesome. Hey, guys, you know that biology considers birds to literally be dinosaurs now, right? Dinosaurs quit being extinct. You probably have members of clade Dinosauria, in the Dinosauriformes, in your yard right now.

That's a pretty nice trade, isn't it?
posted by Mitrovarr at 1:44 PM on October 2, 2014 [4 favorites]


I'm just sad Claire Danes got saddled with this once it descended into the miasma of season 2. Kind of like I felt for Anna Paquin. Well, they get paid, I guess.
posted by angrycat at 1:50 PM on October 2, 2014


yeah that wasn't about Pluto at all, was it
posted by angrycat at 1:51 PM on October 2, 2014 [3 favorites]


Personally I'm fine with 8 planets, but still, if I ever find my self owed a favor by Patrick Stewart, I will ask for payment in the form of an audio recording saying, "There... are... nine... planets!"
posted by ckape at 1:56 PM on October 2, 2014


You probably have members of clade Dinosauria, in the Dinosauriformes, in your yard right now.

That's a pretty nice trade, isn't it?


Not unless my yard is on the tenth planet in our solar system, Pluto.
posted by Brandon Blatcher at 2:09 PM on October 2, 2014


Damning scientific taxonomy because it screws up your astrological system.

No, I'm saying that the astrology software author doesn't even interpret the modern taxonomy correctly, he incorrectly groups Chiron/P95 with the planets, rather than with the Centaurs (which his software allows you to disable and ignore). I do not accept Chiron as a planet, but the software forces it on me.

Personally, I don't go for that antiquated mystical mumbo jumbo, like Hellenistic or Persian astrology. It has to be modern and scientific, which starts with Kepler. But you have to cut it off somewhere in the early 20th Century at the end of the Occult Revival, or else you have to accept weirdos like the Hamburg School. So here's the structure of the Keplerian solar system I'd approve of:

Luminaries: Sun and Moon
Minor Luminaries (planets): Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto.
Moons: Luna, Phobos, Deimos, The Gallileian Moons, and any large object orbiting a planet.
Gravel: TNOs, asteroids, comets, and other insignificant space junk with irregular orbits.

This is a wonderful bit of satire, right?

That is a very interesting remark. But I cannot tell. Today Mercury is transiting in opposition to my natal Mercury, so I am likely to be arguing at cross-purposes with myself. And since Mercury is also conjunct my natal Neptune, I would not realize this is happening.
posted by charlie don't surf at 2:42 PM on October 2, 2014 [1 favorite]


And since Mercury is also conjunct my natal Neptune...

As an Englishman not totally au fait with things medical, I hope your condition is covered under ObamaCare.
posted by Wordshore at 2:51 PM on October 2, 2014 [1 favorite]


Christine Lavin's Planet-X (WARNING: Contains Folk Music)
posted by mikelieman at 2:52 PM on October 2, 2014


And now that puffya has clued me in to how eccentric Mercury's orbit is, I'm wondering whether we're seeing it near a point of minimal orbital inclination, and whether in the future it will orbit significantly out of the ecliptic.

I can't find anything quickly specifically about Mercury's inclination history, but Mercury is currently only about half as eccentric as it ever gets. (It's in 3:2 a spin-orbit resonance, which means that Mercury rotates on its axis three times for every two times it goes around a sun.) The eccentricity varies chaotically from 0 to 0.45, so we're at an average value now.

But! Thanks to the chaos of potential future interactions with Jupiter, it turns out that there is a 1-2% chance that sometime in the next 5 billion years Mercury (or, in other scenarios, Mars) will be ejected from the solar system or crash into the Sun or another planet, like say Earth. This won't happen in the next 40 million years or so, but after that all bets are off on the number and orbits (and habitability) of even the eight things most people agree are "real" planets.

What I'm saying is, you never quite know where you stand with planets. They're constantly moving about and messing with your world view. Nomenclature is really the least of our problems.
posted by puffyn at 2:56 PM on October 2, 2014 [1 favorite]


sometime in the next 5 billion years Mercury (or, in other scenarios, Mars) will be ejected from the solar system

An event that will sound like this.
posted by George_Spiggott at 3:21 PM on October 2, 2014


We trans-neptunian objects (TNOs) don't get no respect!
posted by sedna17 at 4:09 PM on October 2, 2014 [2 favorites]


I'm not particularly attached to Pluto as a planet, but the IAU definition is a stupid-ass arbitrary one back-engineered to exclude Pluto and it appears to have been generated by internal politics, not science. As far as I can tell, faced with the fascinating prospect of more planets, a large sector of astronomers turned tail in terror. I'd have preferred that they just said something like 'larger than 3000km' or something, at least it would have been *honestly* arbitrary.

In reality, we have four serious planets, a bunch of bits of rocks inside their orbit, and a bunch of bits of rock and ice outside them. Personally, I'd kick Mercury out before I'd kick Pluto -- Pluto has a complex moon system, atmosphere, and possibly even rings, and they both are equally eccentric and smaller than the largest moons in the system.
posted by tavella at 4:11 PM on October 2, 2014 [3 favorites]


I don't want these dwarf planets coming to my neighbourhood playing their music and demanding their rights
posted by um at 4:31 PM on October 2, 2014 [1 favorite]


On the plus side, though, they'll do a lot to help regulate your rat planet population.
posted by Wolfdog at 5:10 PM on October 2, 2014


Pluto will always be a planet to me. Do you look at a dwarf on the street and say "You're not a person, you're only a dwarf person?" No you do not. Because that would be awful. I won't do that to my planet buddy Pluto, either.

Also, super excited about New Horizons.
posted by Devils Rancher at 8:04 PM on October 2, 2014 [1 favorite]


If you think things are contentious now, just wait until we get to the point where we can detect Pluto-sized objects in other systems. "What the hell IS that thing anyway?"
posted by happyroach at 1:11 AM on October 3, 2014


> "As far as I can tell, faced with the fascinating prospect of more planets, a large sector of astronomers turned tail in terror."

I do not think you know many astronomers.
posted by kyrademon at 1:27 AM on October 3, 2014 [2 favorites]


Some comments:

1) What's wrong with just saying there are 13 (or 20ish) planets in orbit around the sun?

Nothing, really ... but bear in mind that's not going to be the case under any definition. There are 5 dwarf planets currently recognized (Ceres, Pluto, Haumea, Makemake, Eris), and another 10 or so identified as probably fitting the definition (Orcus, Ixion, 2002 MS4, Salacia, Varuna, 2005 UQ513, Quaoar, 2007 OR10, 2007 UK126, and Sedna). But once all the objects in orbit around the Sun are discovered and catalogued, there are actually probably going to be more like 10,000 of these. That'd be a heck of a mnemonic to memorize.

2) It shouldn't matter how many there are, it's either a planet or it's not. Isn't the "clearing out its orbit" definition arbitrary and stupid?

In some ways, but it's actually not as arbitrary as it seems. The objects we currently call planets formed in part by an accretion process which involved them sucking in most of the little objects in their orbital path. It's basically saying, "Objects we call planets went through a certain formation process, and dwarf planets in contrast never completed that process". As with all definitions of similar objects, there is definitely a certain fuzziness there, but it's not really a way of saying "We don't like 'dwarf planets' because they're little so we're going to seize on this totally random bullshit that lets us say they aren't planets".

3) The outer planets and inner planets had different formation mechanisms from each other, too. Why are *they* all still planets?

In some ways, sure, these are two classes of objects (often divided into rocky planets and gas giants or Jovian planets). In other ways, they shared formation mechanisms that the dwarf planets didn't. Of course, the same could be said about planets and dwarf planets. And the same could be said about planets/dwarf planets and asteroids. And about planets/dwarf planets/asteroids and dust. So the question becomes, where to draw the line?

And again, where that line has currently been drawn is in some ways arbitrary and in some ways meaningful. It's mostly that the word has traditionally meant "rocky planets and gas giants, but not asteroids in a belt even if they're pretty big ones". So Ceres got found in an asteroid belt and (mostly) didn't get called a planet. When Pluto was found, they didn't know it was in a belt, so called it a planet. Then they found out it's in a belt.

So, as more an more objects in this belt got found, the question became, should we keep the old definition and say Pluto got grandfathered in by accident, or change the definition and add Ceres, Pluto, and eventually 10,000 other objects? Since there was actually a fairly sound reason for making a distinction based on the accretion mechanism anyway, they decided to just keep the old one. Which means Pluto got booted.

I'll freely admit there's no *particular* reason not to change the definition of "planet" to "an object in hydrostatic equilibrium that isn't a satellite and doesn't undergo fusion". But we'd need to then have several distinct classes of planets to talk about them sensibly (i.e. dwarf planets, rocky planets, gas giants, brown dwarfs), and I suspect you'd hear a lot of "the rocky planets and gas giants ..." and everyone would grouse that the old way was easier and took fewer words. And there's also no particular reason *not* to keep the traditional definition of planets (rocky planets and gas giants), and say the other things aren't planets. But in either case, Pluto is going to get classed with the dwarf planets and isn't going to be a part of any solar system mnemonic unless that mnemonic ends up as long as the Communist Manifesto.
posted by kyrademon at 2:57 AM on October 3, 2014 [4 favorites]


And now that puffya has clued me in to how eccentric Mercury's orbit is, I'm wondering whether we're seeing it near a point of minimal orbital inclination, and whether in the future it will orbit significantly out of the ecliptic.
Not only is Mercury's orbit eccentric, but that eccentricity is precessing towards a possible resonance with Jupiter's. There's apparently something like a 1% chance that, in roughly a billion years, Mercury's orbit will get dragged to such an eccentricity that it will collide with Venus or even Mars or Earth. With Mars, even a near-miss would wreck Mars' orbit badly enough to risk it eventually colliding with Earth.
posted by roystgnr at 7:51 AM on October 3, 2014


So basically Mercury is the trouble maker of the solar system.
posted by Brandon Blatcher at 8:01 AM on October 3, 2014


So basically Mercury is the trouble maker of the solar system.

No, the dangerous gravitational perturbation is caused by Nemesis.
posted by charlie don't surf at 9:34 AM on October 3, 2014


Quaoar

I think you're misspelling that.
posted by benito.strauss at 9:40 AM on October 3, 2014


But once all the objects in orbit around the Sun are discovered and catalogued, there are actually probably going to be more like 10,000 of these. That'd be a heck of a mnemonic to memorize.

Just call Wakko.
posted by Buttons Bellbottom at 9:57 AM on October 3, 2014


But once all the objects in orbit around the Sun are discovered and catalogued, there are actually probably going to be more like 10,000 of these. That'd be a heck of a mnemonic to memorize.

But why should "you can make a simple mnemonic for it" matter? Going back to my countries analogy from earlier, does it matter if you can name all 195 officially recognized countries? (I had to look that number up. And my ninth grade geography teacher was old school and made us reproduce a map of the world from scratch, without notes.) The number changes. The names change. The borders change. It's more important to know something about various regions of the globe, and about certain major countries (however you want to define that). But listing them all in order of size or whatever? That's why they have the internet.

I would be happy if what kids took from the whole Pluto-is/is-not-a-planet debacle is the idea that the solar system is vast and contains multitudes, and is constantly changing (both literally and in our understanding of it). Sure, you could just teach the eight-planets-and-an-asteroid-belt model that shows up everywhere. But it's wrong and misleading. It misses the whole scale of everything. It's like being happy if kids can name the six continents (because who cares about Antarctica/the Kuiper Belt) and ignoring:

Hundred of satellites, some of which are planet-sized worlds with atmospheres and lakes and geysers and volcanoes. We don't know how many moons there are, because we keep finding new ones, and maybe some are forming right now.

The asteroids that are NOT in the main asteroid belt, some of which occasionally explode over major cities.

The Kuiper belt (which is way bigger and more massive than the asteroid belt and has all these big interesting worlds that we barely know anything about, and hmm, can you see my professional bias? :) )

Comets, like the one we have a spacecraft around right now

The thousands of stars that we know have planets or good planet candidates, most of which look nothing like our own solar system.

And yes, it misses the dwarf planets. By saying "there are eight planets, whose names you should know, and a bunch of dwarf planets, who will not be on the test", you're really saying the little things don't matter. But in terms of active research right now, with the exception of Mars and Mercury, all the exciting missions these days are to small bodies like comets and asteroids and satellites* and dwarf planets. (Yeah, sure, Cassini is orbiting Saturn, but we all know it's really there for the moons.)

So no. I don't expect school kids to memorize the names of all 10,000 to-be-discovered dwarf planets, just like I don't expect them to be able to rattle off fun facts about every exoplanets discovered by Kepler, or for that matter name every country in Europe or Africa along with its capital city.

But they need to know that Pluto is a world, like Ceres is, like Haumea, like Sedna, like some other cool planet we haven't even found yet. They're just in unusual places, and they're not satellites. Calling them "planets" is a way of saying, look, there are space rocks, and then there are space rocks, and here's a bunch of little planets that you may find more interesting than boring ol' Mercury or Uranus**.

*Okay, fine, while the other links are to missions currently in progress, the Titan boat has been snubbed in favor of some dumb Mars** mission. Sniff.

**No offense to Mercury or Uranus or Mars. Some of my best friends study Mercury and Uranus and Mars. Your favorite planet is awesome, too.
posted by puffyn at 3:03 PM on October 3, 2014 [3 favorites]


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