Sad about Pluto? How about 110 planets in the solar system instead?

March 23, 2017 11:15 AM

Kirby Runyon and five fellow science team members from the New Horizons mission to Pluto are at the 48th annual Lunar and Planetary Science Conference (LPSC) in Texas this week, promoting an alternative planetary definition (PDF, 2 page paper; PDF of their poster). They are offering a drastically different definition from the one the International Astronomical Union (IAU) set in 2006 (previously), one which would increase the planet count from 8 to 110 in our solar system.

In 2005, three smaller celestial bodies were proposed to be upgraded to planets by the IAU, but instead of expanding the definition, it was restricted slightly in 2006 (PDF of Resolution B5, "Definition of a Planet in the Solar System") to keep out the riff-raff, er, dwarf planets. The 110 figure comes from a chart of every round object in the solar system under 10,000 kilometers in diameter, to scale, with the definition for a planet being "a sub-stellar mass body that has never undergone nuclear fusion and that has enough gravitation to be round due to hydrostatic equilibrium regardless of its orbital parameters." And instead of a ridiculously long mnemonic device, Runyon and his partners suggest teaching zones, not planet names:

Rocky and metallic inner planets (Mercury, Venus, Earth, Moon, Mars, Ceres) formed in the Inner Zone where heavier elements concentrated closer to the Sun during Solar System formation. Gaseous and mainly icy planets (Jupiter, Saturn, Uranus, Neptune, and their satellite planets) formed in the Middle Zone. Icy planets, most of which are probably dwarf planets (which are"full-fledged" planets) formed in the Outer Zone where lighter elements remained during Solar System formation.

The Washington Post sought early comments from Kirby Runyon and other scientists:

“It's a scientifically useful bit of nomenclature and, I think, given the psychological power behind the word planet, it’s also more consumable by the general public,” Runyon said.

“A classification has to be useful, or else it’s just lipstick on a pig,” countered planetary scientist Carolyn Porco. Runyon's definition “is not useful at all.”
...
“If you look at the solar system with fresh eyes, it is really hard to not realize that there are eight big things dominating the solar system and millions of tiny things flitting around,” said Caltech astronomer Mike Brown, whose discovery of the dwarf planet Eris, announced in 2005, precipitated the IAU vote a year later.

Brown was not at that vote, but he said that a definition based on orbital dynamics “is the most profound classification you can come up with.”

“That’s the one that asks the question we’re asking as planetary scientists,” he explained. “Why did the solar system form with these eight giant things and all these other things around them?”

In short, the debate rages on.

posted by filthy light thief (68 comments total)

Can we just grandfather in Pluto and be done with it?
posted by rouftop at 11:20 AM on March 23, 2017 [8 favorites]

“That’s the one that asks the question we’re asking as planetary scientists,” he explained. “Why did the solar system form with these eight giant things and all these other things around them?”

Well that's just begging the question, isn't it?
posted by dbx at 11:20 AM on March 23, 2017 [1 favorite]

I'm not sure if those zones are something unique to their proposal and presentation, as I didn't find any other images or definitions like theirs. I did find this page on solar systems with a similar image, with a larger version found on an Indonesian page on Twin Star Theory from R. A. Lyttleton, which has the largest image of these zones.
posted by filthy light thief at 11:21 AM on March 23, 2017

This is why we have adjectives, folks! Terrestrial planets. Gas planets. Small planets. They're all planets!

GRAMMAR GETS THE JOB DONE! ESCHEW FALSE BINARIES!
posted by Celsius1414 at 11:21 AM on March 23, 2017 [19 favorites]

You know they're just in the pocket of Big Planet Namer.
posted by tittergrrl at 11:23 AM on March 23, 2017 [3 favorites]

Can we just grandfather in Pluto and be done with it?

We could, but if you look at the chart of smaller round objects, you'll see that Ganymede and Titan are both bigger than Mercury, then Callisto, Io, the Moon, Europa and Triton are larger than Pluto, and Eris is a bit smaller than Pluto. From there, the sizes drop again.
posted by filthy light thief at 11:24 AM on March 23, 2017 [2 favorites]

So that just means we can add Eris, right?
posted by Zalzidrax at 11:25 AM on March 23, 2017 [1 favorite]

I think we need rational and irrational planetary models. That way I can just be irrational and have Pluto as a planet and no one has to fight me anymore.
posted by Annika Cicada at 11:32 AM on March 23, 2017 [3 favorites]

I, for one, welcome our new planet overlords
posted by blakewest at 11:33 AM on March 23, 2017 [2 favorites]

Pluto is definitely a planet, so is Ceres. I am not sure all the moons need to be planets, but that's still quite coherent, unlike the contrived reasoning for excluding Pluto. The IAU needs to face reality. There are 100+ planets. Deal with the terrifying grandeur of nature, don't deny.
posted by save alive nothing that breatheth at 11:43 AM on March 23, 2017 [7 favorites]

The orbiting bodies of the Solar system are Jupiter, Saturn, Uranus, Neptune, and miscellaneous assorted debris.
posted by Faint of Butt at 11:45 AM on March 23, 2017 [29 favorites]

Oh hell yeah! The initial change was silly and seemed born of fear (just too many to count, oh noes). It's a real stunted view, that a planet must be big.
posted by Brandon Blatcher at 11:46 AM on March 23, 2017

I'm not sure I can do a mnemonic for 110 names.

Just start naming them after digits of pi.
posted by Etrigan at 11:51 AM on March 23, 2017 [1 favorite]

Science you so wacky.

Just what is so special with the word "planet"?

How about "that big rock" in the sky, as in "Uber-space-shuttle take me to the big rock Ceres".

"I live on a bigger rock than you martian kid"

"My mother in law is so big she's at home on that big rock Jupiter"
posted by sammyo at 11:51 AM on March 23, 2017

If we named the planets after Pokemon, we wouldn't even need to bother with mnemonics.
posted by J.K. Seazer at 11:53 AM on March 23, 2017 [13 favorites]

All we need to get this done is to award corporate naming rights.

"Okay, focus your telescope. That one up there, that's Mars, you're right! And to its left are Red Bull -- see its wings?, you can see Wells Fargo in its eternal dance with Bank of America; wait! they just merged. There's the constellation Mickey the Mouse, there's Windows 11, there's Spaceballs: The Planetoid..."
posted by delfin at 11:54 AM on March 23, 2017 [2 favorites]

“A classification has to be useful, or else it’s just lipstick on a pig,” countered planetary scientist Carolyn Porco.

I see what she did there. And I like it.
posted by The Bellman at 11:55 AM on March 23, 2017 [7 favorites]

Mercury Venus Earth Mars Astroids Jupiter Saturn Uranus Neptune Pluto.

Mother very easily made a jam sandwich using no peanuts (mustard, or glue*).

*For universes (such as RAW's) in which Mickey and Goofy are also planets.
posted by The Bellman at 12:00 PM on March 23, 2017 [3 favorites]

Spaceballs: The Planetoid...

Don't give bored astronomers any ideas...
posted by Zalzidrax at 12:04 PM on March 23, 2017

This is all some inyalowda prejudice against the outer planets my beratnas!
posted by rhamphorhynchus at 12:11 PM on March 23, 2017 [5 favorites]

House arrest for these troublemakers! Everyone knows there are only 8 planets, and Earth is at the centre of them!
posted by rodlymight at 12:16 PM on March 23, 2017 [1 favorite]

So that just means we can add Eris, right?

Well, sure, but the difference between Eris and the next largest object not orbiting another planet isn't that big. (Makemake is about 2/3s the size of Pluto and Eris). So it's not like that would be a particularly principled stand.

If we want to make the criteria completely arbitrary so as to only include the planets that were considered planets when we were kids, why not just decide that the cut-off is 1,170 kms of median radius, and just be up front that the only reason for that number is because it's 7km more than Eris' radius and 17 less than Pluto's?
posted by firechicago at 12:20 PM on March 23, 2017 [3 favorites]

For just about every other class of celestial object, we gave up on the idea that each and every one needs to have a classical name. The recognition that there are countless red giants in the universe doesn't change Betelgeuse's cultural importance. The algorithms that uncovered thousands of planets from the Kepler survey don't change how I do planet-spotting for Venus, Mars, and Jupiter in the night sky. Haley's Comet has a rich literature and folklore even though automated sky surveys discover new comets and asteroids by the dozens. Hubble's deep field photographs doesn't change the importance of the LMC and SMC to the southern sky.

I don't see a problem with having a list of "classical" planets alongside our classical stars, nebulae, clusters, and galaxies. These are the objects that can be spotted with very good eyes, binoculars, or backyard telescopes. We give them historical and cultural distinction, not because they're members of a unique class, but because they inspired astronomers to search for thousands more.

Then the planetary geologists can get on with their studies of how gravity, internal heat, orbital dynamics, and phase transitions influence the features of objects large enough to create those dynamics.
posted by CBrachyrhynchos at 12:29 PM on March 23, 2017 [6 favorites]

Basing the definition on roundness makes sense, but it seems like it's still useful to talk about "things that directly orbit a star" versus "things that orbit things that orbit stars" versus "things that orbit stars alongside a bunch of other things of about the same size".

I don't mind so much having a word that means "round planets, moons, and asteroids", but I feel like we should reserve the word planet for "round things that directly orbit a star." Or come up with a new word for it, if "planet" is to become such a generalized term.
posted by jedicus at 12:32 PM on March 23, 2017 [4 favorites]

I'm not sure I can do a mnemonic for 110 names.

It'd be like a Fiona Apple album title. (cheeky face)
posted by robotmachine at 12:36 PM on March 23, 2017 [6 favorites]

We could, but if you look at the chart of smaller round objects, you'll see that Ganymede and Titan are both bigger than Mercury, then Callisto, Io, the Moon, Europa and Triton are larger than Pluto, and Eris is a bit smaller than Pluto. From there, the sizes drop again.

There are two types of people when the question of Pluto comes up: Those who say it's a slippery slope to include Pluto in the definition of a planet because then we'd have to include 100+ other things, and then those who respond to the first group by saying "Yep!" with a big grin on their face.
posted by Nonsteroidal Anti-Inflammatory Drug at 12:36 PM on March 23, 2017 [6 favorites]

I find the new definition more broad than I'd prefer, but by golly, it's simple, it's clear, and what's most important, it's NOT arbitrary.

I hate the current IAU definition with a passion, because it's fundamentally rooted in the notion that the list of planets should be small and memorizable.
posted by tclark at 12:46 PM on March 23, 2017 [1 favorite]

“If you look at the solar system with fresh eyes, it is really hard to not realize that there are eight big things dominating the solar system and millions of tiny things flitting around,” said Caltech astronomer Mike Brown

I love this description, especially in contrast to the discussion about terminology.
posted by Autumnheart at 12:47 PM on March 23, 2017

"If you look at the solar system with fresh eyes, it is really hard to not realize that there are eight big things dominating the solar system and millions of tiny things flitting around,” said Caltech astronomer Mike Brown

Probably nine counting the highly probable super-Earth out there beyond Neptune. But has that really "cleared its orbit" when the evidence pointing to it involves eccentric plutinos in overlapping resonant orbits?
posted by CBrachyrhynchos at 12:52 PM on March 23, 2017

Autumnheart: I love this description ["there are eight big things dominating the solar "], especially in contrast to the discussion about terminology.

Counterpoint: Ganymede and Titan are bigger than Mercury, and even though they orbit larger bodies, they both have significant features.

While Titan is "only" a moon of Saturn, it's the only moon known to have a dense atmosphere, and the only object in space other than Earth where clear evidence of stable bodies of surface liquid has been found, while Ganymede, the largest and most massive moon of Jupiter, lacks an atmosphere, it is the only moon known to have a magnetic field, two similarities with Mercury.
posted by filthy light thief at 12:59 PM on March 23, 2017 [3 favorites]

I (a layman with strong opinions) think the best argument in favor of a re-redefinition is that the old definition is impossible to apply outside the solar system—many extrasolar planets have been discovered, many of them super-Jupiters, but we can't know if they're "planets" or "dwarf planets, which aren't planets [spit]" because we don't know if they've cleared their orbits or not.

I basically love everything about this proposal except for "moon planet". Call the general category "planet", maybe, with subcategories "major planet" (round and zone-clearing), "dwarf planet" (round but not zone-clearing), "planet" (round, zone-clearing or not), and "minor planet" (not round). But reserve a special term "moon" for objects orbiting planets, possibly with the same "major/dwarf/minor" subcategories.
posted by The Tensor at 1:01 PM on March 23, 2017

As far as arbitrary definitions go, scientists lost all my respect back in the 80s when they defined the meter as "the length of the path travelled by light in vacuum during a time interval of 1/299792458 of a second." Because, really? That's just making things complicated for the sake of making things complicated. 1/300000000 is better in almost every respect. In fact, I would encourage you to go ahead and remember that number, and the next time it comes up (at some cocktail party, I would imagine) you can say, "the speed of light is 300,000,000 meters per second," and then follow up (as you push your glasses up over the bridge of your nose) with, "approximately." It is unlikely that anyone will correct you with the exact figure.

In a similar vein, the best thing that I can say about the current definition for planets, which includes Saturn and Mercury as the same class of object, while excluding Ceres, is that it must have been carefully chosen. I'm fond of the traditional definition of planet, which includes everything in the sky that moves, but doesn't include the Earth.
posted by surlyben at 1:01 PM on March 23, 2017 [1 favorite]

"the length of the path travelled by light in vacuum during a time interval of 1/299792458 of a second." Because, really? That's just making things complicated for the sake of making things complicated.

It's really not. If they did that, a kilometer would be 60 centimeters longer, and every unit that relies on meters would need to be adjusted by a factor of 6/10,000.

That may not sound like much, but a difference of 6 in 10,000 adds up FAST when you're talking about precision measurement. It's really a world of difference.

It's unfortunate that our original estimation of the meter (which was 1/10,000,000 the distance from the pole to the equator) just happened to be so close to 1/300,000,000 of the speed of light, but fixing that coincidence, while it would be wonderfully parsimonious, is hugely, vastly, ridiculously impractical. It's not arbitrary.
posted by tclark at 1:43 PM on March 23, 2017 [6 favorites]

But I don't WANT other planets. I want PLUTO back.

::sniff::
posted by Splunge at 1:45 PM on March 23, 2017 [2 favorites]

but fixing that coincidence, while it would be wonderfully parsimonious, is hugely, vastly, ridiculously impractical

I don't think I like your attitude, mister.
posted by Faint of Butt at 1:53 PM on March 23, 2017 [1 favorite]

A little far down in the thread to add this, but Stuart Robbins of the Exposing PseudoAstronomy Podcast interviewed Kirby about his proposed definition in the latest episode (Episode 159 - A Proposal for the Geologic Definition of "Planet," Interview with Kirby Runyon). Both worked on different aspects of the NASA New Horizons mission to Pluto.
posted by Decimask at 1:58 PM on March 23, 2017 [2 favorites]

that the old definition is impossible to apply outside the solar system

The IAU definition deliberately and explicitly only applies to the Solar System. Exoplanets are their own thing.

a celestial body that (a) is in orbit around the Sun

posted by zamboni at 2:01 PM on March 23, 2017

> "It's a scientifically useful bit of nomenclature ..."

...

How?
posted by kyrademon at 2:04 PM on March 23, 2017

For the first half of the 19th century, Ceres was a planet. Then, as we discovered similar objects in the same region of space, it was reclassified.

Pluto was a planet for about 75 years. Then, as we discovered similar objects in the same region of space, it was reclassified.

So what's the difference?

Obstinate boomers.
posted by thecjm at 2:12 PM on March 23, 2017 [8 favorites]

I'd say there isn't a difference, and as we understood the solar system better, we should have put Ceres back *onto* the list rather than taking Pluto off for spurious reasons.
posted by tclark at 2:17 PM on March 23, 2017 [2 favorites]

CBrachyrhynchos: Probably nine counting the highly probable super-Earth out there beyond Neptune.

What now? Ooh, Planets beyond Neptune is a fascinating Wikipedia page, as is the page for Planet Nine, aka "perturber," "Jehoshaphat" (Phattie for short?) or "George."
posted by filthy light thief at 2:22 PM on March 23, 2017

I don't think I like your attitude, mister.

I, on the other hand, really like tclark's attitude. I've been waiting for someone to properly rebut me on this point since 1993, at least. I do note that the original meter proposal from 1795 had a comparable degree of uncertainty, and since they were changing the unit anyway, every unit in the world that relies on meters was already going to have to be adjusted, in theory anyway. In practice, the change was so small that most applications could ignore it.

Part of me thinks that nobody worries about all the things that have to change when they redefine "planet", but I guess none of those things have engineering consequences. I guess count me as partly convinced. (The 20 year old me, who had to memorize the stupid 299792458 number, will never be convinced.)
posted by surlyben at 2:24 PM on March 23, 2017 [1 favorite]

This is all some inyalowda prejudice against the outer planets my beratnas!

Kopeng mi, first they name the planets and then they try to take the sky, koyo!
posted by corb at 2:27 PM on March 23, 2017 [3 favorites]

I'd say there isn't a difference, and as we understood the solar system better, we should have put Ceres back *onto* the list rather than taking Pluto off for spurious reasons.

I'm okay with this. Right now, the options for number of planets is 8 (what we're at now, big enough to be both round and clear it's orbit), 13 (big enough to be round and is orbiting the sun and not another planet), or 110 (big enough to be round, not big enough to be or have once been a star).

9, you'll notice, is not an option.

The idea of grandfathering in Pluto, not for any scientific reason, but "because that's the way when I was a kid and therefore it should never change/won't someone think of the children," is what I'm cranky about.
posted by thecjm at 2:31 PM on March 23, 2017 [10 favorites]

The idea of grandfathering in Pluto, not for any scientific reason, but "because that's the way when I was a kid and therefore it should never change/won't someone think of the children," is what I'm cranky about.

This seems like a good time to confess that, as a non-astronomer, my only dog in this fight is that I have a particular relative who is very tediously vocal about how Pluto is a planet. I support the 8 planet definition just to continue to annoy her.
posted by dismas at 2:49 PM on March 23, 2017 [2 favorites]

A planet is what, when you stop believing in it, doesn't go away.
posted by delfin at 3:51 PM on March 23, 2017

Semantics are a sign of vision loss.
posted by Mblue at 4:46 PM on March 23, 2017

Back around 2010, I made an 8-part "Dwarf Planet Suite" of synth string-patch improvisations as a parody of Holst's planets, based upon Wikipedia's list of Trans-Neptunian Objects at that time. If I take this current interpretation seriously, then I'll just have to make another 102 or so improvisations. Which is not impossible, but unlikely.
posted by ovvl at 5:21 PM on March 23, 2017

I have an alternate answer for "What is a Planet?" ... It is something that humans permanently live upon. Right now, there's only the one. Get busy if you want Pluto to be another one.
posted by Xyanthilous P. Harrierstick at 5:38 PM on March 23, 2017 [3 favorites]

Flagged for "we already have a current thread about pointless arguments"
posted by Wolfdog at 6:11 PM on March 23, 2017 [4 favorites]

Or see.
posted by Mblue at 6:19 PM on March 23, 2017

So, given that the Oort cloud may extend a substantial fraction of the distance to the nearest star (note that the furthest zoom-out in the first link I give there barely shows the inner edge of the Oort cloud, and that the scale in the second link is logarithmic), could this mean that we haven't discovered most of the planets in our own solar system yet?
posted by XMLicious at 6:51 PM on March 23, 2017

I feel like we should reserve the word planet for "round things that directly orbit a star."

That is what it's meant in ordinary language for a hundred years or more and I don't see any reason to change it, but it seems to be fashionable to come up with other ideas lately so I propose: "anything in the sky is a planet, including birds."
posted by sfenders at 8:06 PM on March 23, 2017 [3 favorites]

They could call Jupiter, Earth, etc. planets and bootleg knockoffs like Pluto, Triton etc. planetes and hope nobody notices.
posted by xigxag at 8:12 PM on March 23, 2017 [1 favorite]

On second thought I'm pretty sure George R. R. Martin would call Pluto an upjumped "hedge planet" so there's that as well.
posted by xigxag at 8:14 PM on March 23, 2017

It'll be almost impossible to tell whether specific Kuiper Belt Objects meet the proposed definition.
posted by mark k at 10:28 PM on March 23, 2017

The key thing I think is, Mercury and Jupiter aren't the same class of object. Call anything from 2000km average radius up to 20000km a planet, and that gets you the terrestrial planets, the interesting moons, Pluto and Eris. Over 20000km radius and it's a giant planet, less than 2000km and it's a minor planet. The number is somewhat arbitrary but astronomy does that all the time with classes of star and such. The 2000-20000 km radius band contains all of the big rocky objects that can hold some atmosphere and have surface features other than craters but aren't primarily made up of gas like the big failed star that is Jupiter or ice like Neptune.

Yes, this makes some moons into planets, but Ganymede and Titan and Io and Callisto and Europa and Triton and our Moon are all more interesting than Mercury anyway, and kids should know what they are. There would be 4 giant planets, 6 planets, 7 satellite planets, and a whole bunch of other crap. Kids love sorting things into categories like that.
posted by graymouser at 10:35 PM on March 23, 2017 [1 favorite]

Brown blathering out about how there are 8 big objects and it's all so obvious is what is a planet utterly pisses me off about the current definition. Because there aren't 8 big objects. There are 4 big, serious planets and then there are a bunch of rocks inside their orbits and outside their orbits. Because we live on one of the little round rocks we define it as special, and because three of the other rocks have long histories in our mythology we also count them as special. And if the definition was 'earth, the classical planets, plus the other two that are so big we can't ignore them' I'd be fine because it's honest. But the ridiculous pretense that Mercury (a tenth the diameter of even the smallest gas giant, smaller than two gas giant *moons*) is super special and clearly in the same class as Jupiter but Pluto (half the diameter of Mercury) is definitely totally different from Mercury is just dumb. So we got this desperate retconned illogical definition to try to keep the list short.
posted by tavella at 10:44 PM on March 23, 2017 [2 favorites]

"Students May Very Easily Master Astronomy Just Sit Up Nights Practicing."

Wait, isn't the mnemonic "King Phillip Came Over From Great Spain"?

You know, for Kercury, Phenus, Cearth, Oars, Fupiter, Gaturn, and Suranus? (I do not recognize Neptune as it may not be spotted with the naked eye. I only accept naked astronomy. You know, like the Greeks did it.)
posted by Eyebrows McGee at 10:45 PM on March 23, 2017 [1 favorite]

"eight big things"? The Solar System has moons larger than the planet Mercury.
posted by anonymisc at 12:46 AM on March 24, 2017 [1 favorite]

Well that would really change the astrology column a bit.
posted by boilermonster at 12:56 AM on March 24, 2017

#fakeplanets
posted by walrus at 2:08 AM on March 24, 2017 [1 favorite]

Man, I ain't got no time for no dinky-ass "planets." Although I'm for letting Pluto back in if it turns out that Charon is really the Charon Relay.
posted by Halloween Jack at 4:39 AM on March 24, 2017

These guys really want Pluto to be called a planet. I followed the New Horizons twitter feed while it was en route, but had to stop because so many of the tweets day after day were campaigning to bring back planet status. Just seemed unseemly for scientists to be propagandizing so much.
posted by gubo at 5:20 AM on March 24, 2017

Well that would really change the astrology column a bit.

Could be a bit of a boon to the industry, really. Especially if they name one of the new planets Rupert.
posted by Anticipation Of A New Lover's Arrival, The at 5:28 AM on March 24, 2017

The only reasonable course of action is to expel the extraneous celestial bodies from our solar system.
posted by bracems at 6:10 AM on March 24, 2017 [1 favorite]

Whatever. Just don't let planets made of phlegm into the club.
posted by kozad at 10:29 AM on March 24, 2017

I can't help but feel (not that I'm biased) that a lot of this comes down to the philosophy of science. The question "what is a planet" could be more precisely phrased as "what is the list of planets a list of?"

That's not at all a pointless question! The theory-ladenness of observation means that the preconceptions we use to classify the universe have a real impact on how science progresses. That's not to say (though one could argue) that there will be inaccessible truths, but it will always be faster and easier to draw scientific inferences that neatly fit our theoretical model than ones that complicate or contradict it.

For example, if what one cares about is how planets form, they'll want a simple definition for objects that seem to have resulted from stellar accretion without further chaotic influences, perhaps leading to the IAU's 8-planet model. On the other hand, if what matters most is the expansion of humanity, one would prioritize potentially habitable objects like Europa, Titan, and the Moon, maybe even leaving out the gas and ice giants entirely. If mythology is the thing, one might want to look at a 7-planet model which includes the Sun and Moon— or if that means the mythology of the post-optics era, swap in Neptune and Pluto... and on and on.

Unfortunately, we can't totally escape this by taking a stance of scientific pluralism, by saying that these are merely different classes of a "big planet/little planet" model or such. If one's field needs more public interest and support (and it always does), they really would like for their chosen definition to be the one adopted by popular consensus as being a "real" planet. Suddenly we're facing a political problem— all science is political, of course, but it still bears acknowledging that we're engaging in something more than pure empiricism.

More briefly stated: Tell me what you value, and I'll tell you what a planet is. Complain about the concept of a capricious cabal of administrative astronomers if you wish, but don't try to say they haven't articulated what their values are :)
posted by emmalemma at 10:56 AM on March 24, 2017 [1 favorite]