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> Historically and culturally, Pluto is considered a planet.

A very brief period of history. Give it 50 years and the number of people who will call it a planet will be close to 0.

Let's not overstate Pluto's significance in culture. People call it a planet only because that's what they were taught in school. Not because of other (very few) cultural references. As it has been dropped from the curriculum, so shall it be dropped from people's minds.

Compared to the other planets it's rarely referred to in stories, etc. It has very little significance in today's culture beyond the fact that it was taught in school.

That's not the case for something like Jupiter. If they decided tomorrow that gas giants are no longer planets, it will remain in arts and culture. Pluto? Highly unlikely.

I don't think my kid knows about Pluto. That doesn't bother me in the slightest.

This is not insignificant. The period of Pluto's planethood represents just about 0.76% of recorded human history, but that does cover around 7% of the total number of people who have ever lived, about 10x the 'average'. Of course a lot of culture comes out of that. I think the 20th century will be important to historians for a very very long time.

> The period of Pluto's planethood represents just about 0.76% of recorded human history, but that does cover around 7% of the total number of people who have ever lived, about 10x the 'average'. Of course a lot of culture comes out of that.

It's an odd way to analyze it. Plenty of things have been known for longer and it doesn't bother us if they're not taught in school, etc.

The meaning of a word comes from how its speakers use it.

When people stop referring to Pluto as a planet, it will cease to be one.

Until then, we are living in a reality in which Pluto both is a planet and is not a planet, depending on the context.

> When people stop referring to Pluto as a planet, it will cease to be one.

I'm not disagreeing. What I'm saying is that compared to most other planets, people are going to stop referring to Pluto as a planet, by the mere fact that they'll stop teaching it in school. It has no cultural momentum unlike Mars, Venus, etc.

Peanuts, cashews, almonds, walnuts, pecans, Brazil nuts and pistachios are culinary nuts but NOT botanical nuts.

Botanical berries: Bananas, tomatoes, grapes, cucumbers, eggplants, avocados and peppers, but NOT strawberries, raspberries, blackberries or mulberries.

Scientists really should have made up their own categories instead of using our words.

Well, the thing is, nobody got told, out of nowhere, that the “honorable strawberries” were now called simply “mildly honored straw,” because a committee of so-called experts had expressed their will, and that now everybody had to say “mildly honored straw” instead of “honorable strawberries,” or else they would be *incorrect*, because the science league said so.

The word “planet” signifying a certain reverence, and the fact that a scientific body was now policing everyday language — for the apparently petty reason that we should not honor Pluto as we once did — it was quite a misstep for how people in the public might view science going forward. Unless, perhaps, the idea was to make people more skeptical of scientific results and statements.

The alternative was to announce "we now have 10 more planets, and there are probably a bunch more, and we'll probably never really get a definitive number".

That would also have had an impact on the public view of science. Perhaps not as bad, but it would have had an impact.

Planets predate modern astronomy. You have to negotiate with the public if you want to change what “planet” means. To most people, in most contexts, it means 8 or 9 specific things that they have specific ideas about, not a theoretical category of infinite objects.

Few things sound more like more science than "planets". Telling people "Well actually 'planet' isn't a scientific term, it's a historical / cultural term" will also significantly reduce their trust and interest in science.

Hey, don’t blame me, blame the IAU for opening that can of worms. I’m just happy calling Pluto a “planet” and would rather the IAU had left me in peace — they’re the ones who want to argue with me about what words I’m supposed to say and when I’m supposed to say them.

I’d encourage you to think about the impact of science fiction on interest in science. Culture is an extremely powerful force. I don’t think your concern would bear out.

There was no do nothing option, the IAU didn't open the can of words. 10 new objects that would be called planets under the old definition were discovered. "Doing nothing" would have led to far more significant changes.

Even if they had to do something, they didn’t need to do what they ended up going for — it was a pretty bad option from a scientific standpoint and a needlessly controversial one.

As the article here explains, the 2006 IAU definition doesn’t really make sense or function as a useful model for what a planet is.

This is similar to how most people would say that mathematics is about numbers, but the word “number” doesn’t even mean anything in math.

> Planets predate modern astronomy.

If we're segmenting off "modern astronomy" then Pluto wasn't even discovered yet.

And we discovered Ceres long before Pluto. It would be pretty rude to keep excluding Ceres just because we knew about the asteroid belt before we knew about the Kuiper belt.

It’s not about being rude to Pluto so much as about being rude to me.

I’m not a member of the IAU. I don’t adhere to their linguistic prescriptivism, and nobody should expect that I will. Some of their own members do not — the article here explains.

Are you a member of the IAU?

I didn't say anything about rudeness to Pluto, I was talking about Ceres. I like Ceres. I think it deserves some recognition for being known before even Neptune.

By all means, call it what you like and honor it however you like.

I’m not the IAU, and I have no interest whatsoever in emboldening thousands of people to smugly harass you or anybody else about it.

No, the alternative would be to make up some latin sounding words for planets, dwarf planets, etc. and leave the vulgar planet alone to the standard 9 that we all know are planets.

This is what should have happened. (And it’s not too late — Pluto will remain with us for a while yet.)

No that would be an argument to return to the original definition of planets (highly visible celestial objects that migrate across the sky, i.e. the Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn).

If you believe in the "standard 9" you're just insisting on returning to a scientific definition of planets but one that is frozen on our scientific understanding from a few decades ago...

As you can see, there are many valid ways to go about understanding what a planet is in a cultural sense.

The argument is to not make any changes to what people call planets but to instead have taken the opportunity in 2006 to create a separate classification system. Use something vaguely Latin sounding like planitus or whatever.

Yes, but again, what people call planets was stable for over a thousand years before changing rapidly in the past few centuries (first with the Sun and Moon being removed during the Copernican revolution, then Ceres, Pallas, Juno, and Vesta being added before being removed when they discovered a bunch of other asteroids, then Neptune being added, and finally in the last century Pluto being added before being removed after they discovered a bunch of other dwarf planets).

If you don't like changes to what people call planets, you should be unrolling all the other changes that have also been made, and go back to the original definition that stood from ~200 BCE-1700 CE.

Right, and then everybody would be in the comments complaining about how "everybody is using a new term for planet and it's ridiculous, just call them planets". It's not a battle that can be won.

"Scientists really should have made up their own categories instead of using our words."

If they could do it all over again probably most of them would. The sciences all grew organically too. Some of these things like "berries" aren't even just the product of one reclassification, they're the product of several over the course of decades or centuries, which is how they get so common-sense silly over time.

We had the perfect opportunity to introduce new names when the IAU created the "dwarf planet" classification in 2006. That was literally the perfect time to do it all over.

Although there may have been a chance from an opportunism standpoint, the wisdom needed to do that well was clearly absent.

> Scientists really should have made up their own categories instead of using our words.

Doesn't really matter. The public would end up taking science words for their own purposes to sound legitimate. Look at how "quantum" and "energy" is used in alternative medicine.

They really are the “epicenter” of the problem

> The actual problem here is weirdly aggressive nerds who are incapable of nuance

This is the actual problem everywhere.

I wonder how happy each group would be by this solution. Planet as a scientific and non-scientific usage.

Conclusively, science class would not teach Pluto as a planet (it should after all stick to the science) and English class will discuss the cultural impact of planet Pluto! Maybe write poems about the importance and impact of 9 word mnemonics? Sounds fun.

My headcanon is that people would hate it so so much! I can't wait to see that as a distant observer.

This would be a really good discussion topic in schools.

People need to understand the dynamic between science and society, because that is an important part of how the world works today.

Pluto is an exemplar.

And also, the value of culture. It might not be a scientific result, but it still shapes our experience of the world. Pluto is beloved.

Pluto makes for a great lesson about science itself. Our view of the universe we live in changes over time as we get more information about it. Children should learn to expect that and to understand that it isn't a bad thing, or a flaw with science, but a vital part of the process and when it happens things are working as intended. That means that today Pluto isn't a planet, even though for a small time it used to be considered one, because we learned more about the bodies in our solar system and it no longer made sense to call Pluto a planet. We can explain to children why it shows up in our history, and how we've moved on.

It honestly doesn't have to be a bunch of drama. The problem will pretty much go away after the current generation who grew up learning about Pluto as a planet dies off and gets replaced by a generation who always knew that there were only 8 planets in our solar system. Hopefully they'll also be better prepared to accept changes that come from better understanding.

I appreciate your contribution to the discussion. I’d have to point out that Pluto both is and is not a planet, depending on the context — it depends on whom you ask and the situation in which you ask.

What would you say to scientists and laypersons who consider Pluto to be a planet? How would you persuade them to your own viewpoint? Please give at least three examples and use at least three paragraphs.

Pluto is a dwarf planet. It feels like less of a "is and is not" situation, and more of an "isn't, but was once thought to be" situation.

Some people remember being told that it was a planet when they were kids and they cling to that even though we've learned that it doesn't make sense to call it a planet anymore.

Apart from that it shows up as a planet in literature, almost all of which was written before we knew better, just like how the idea of earth being at the center of the universe shows up in literature and was once a part of our culture. The geocentric model had passionate holdouts too, but we've mostly moved on from that idea since and I think we're better off for it.

For scientists and laypersons who aren't just holding onto "planet" for sentimental reasons, I'd recommend the book "How I Killed Pluto and Why It Had It Coming"

A geocentric model is observably incorrect.

The word “planet” is neither true nor false. Different people use it to refer to different things.

Kind of like the word “tree.” Some things are trees and some things are not — and it really depends on whom you ask and when you ask them. Most people are able to get along and allow people to refer to whatever trees they want to, because it’s a free country and it really doesn’t make sense to try to control other people over something like that.

> because it’s a free country and it really doesn’t make sense to try to control other people over something like that

No one is trying to control you by defining what words mean. In fact, you're still fully free to call anything you like whatever you want. You risk being misunderstood in certain contexts or assumed to be ignorant in others, but no one will stop you. My guess is that what you personally call a planet or not wont come up very often and will matter very little to anyone else.

A mention of “the planet Pluto” carries risk that you will be derailed by people who think they are very scientific but in fact are just excited to be able to correct someone.

My language has become politicized. Either I go with the flow and surrender something about my own language, or I risk getting called out or misunderstood as being incorrect if I continue.

It’s easier to let them think they corrected you than to explain your position. People believing that correcting others over superficial word choices counts as being scientific… it’s disappointing.

That book title and my vague memory the same author had a hand in naming Eris makes me think they've encountered the Principia Discordia at one time or another.

> Our view of the universe we live in changes over time as we get more information about it.

But that’s not what happened here. The definition was changed. We didn’t learn anything new about Pluto that made us say “ah, we thought Pluto had a solid core but apparently it doesn’t, so it’s not a planet”. All the relevant facts about Pluto remained the same. The reason why it’s no longer considered a planet is because of the term ‘planet’, not because of Pluto.

We didn't learn much more about Pluto, other than it wasn't as unique as we once thought. We learned a lot more about other bodies in the Kuiper belt though. By our old classification, suddenly it looked like there could be hundreds of "planets" in our solar system. Our improved understanding of the nature of the Kuiper belt and its inhabitants caused us to reassess which types of features were useful to distinguish a planet from the vast number of smaller objects in our solar system.

> Pluto makes for a great lesson about science itself.

I disagree. Quibbling about a definition like that is like quibbling about whether a certain bird is a black-crowned Night-Heron or a black-crowned Night Heron (without the second hyphen), which is a real controversy that took place.

I suppose it shows a socially constructed, human aspect of science, but it really has very little to do with actually understanding the universe. The universe doesn’t care about our arbitrary stamp-collection-style classification of objects. There’s no equation or physical theory that describes the difference in any meaningful way.

In a sense you're right, the need to classify things is really for our convenience. Those classifications can be extremely helpful though and it's for that reason that we try to come up with good systems of classification and re-evaluate what goes where as we learn more.

The universe doesn’t care about our arbitrary stamp-collection-style classification of objects, anymore than it cares about where elements sit on the periodic table, but for us humans having things classified and ordered is a big deal. It's our constant arbitrary naming and organizing and classifying that allows letters to get delivered to my house and packets to reach my network. It gives us more precise language and enables better focus on what matters. It helps build a foundation for teaching and research. It helps to catalogue all we've learned. While you'll find plenty of ego fueled petty squabbles around the naming and classifying of things, it's still a pretty big part of what science does and we'd struggle to teach or coordinate any sort of meaningful science without it.

Your point is valid - we do need to classify things for our own mental convenience - but I don't think the Pluto case is an example of it.

In many ways, the Pluto situation is an example of the Buddhist metaphor about the finger pointing at the moon. The finger is not the moon. Obsessing over the definition of "planet" to that degree doesn't actually achieve anything useful - it's a classic example of confusing labels with the thing being labeled.

The Pluto "controversy" was just bad "science" being committed by a committee.

> Your point is valid - we do need to classify things for our own mental convenience - but I don't think the Pluto case is an example of it. Obsessing over the definition of "planet" to that degree doesn't actually achieve anything useful

There are people who feel that it's worth classifying all the objects in our solar system and that doing so is useful. It's pretty much always been that way. The original definition of "planet" was used to classify things visible in the sky and the criteria was simply "stars that moved". The Sun and Moon were "planets". Asteroids were "planets". We've been constantly updating our classifications ever since as new information became available (see https://en.wikipedia.org/wiki/List_of_former_planets).

Pluto was discovered in 1930 after a pair of photographs showed another light in the sky had moved. Until the 1990s we thought Pluto was alone out there at the edge of our solar system, but then we discovered 15760 Albion, followed by another new "planet" named (181708) 1993 FW followed by the discovery of hundreds of other tiny objects until it was realized that Pluto wasn't alone at all. There was a massive belt containing a vast number of small objects past Neptune and Pluto was just one of those small objects (see https://upload.wikimedia.org/wikipedia/commons/5/5b/Kuiper_b...). The discovery of a bunch of objects of similar size and composition to Pluto, Eris in particular, made it clear that Pluto just wasn't like the other planets in our system. We had 8 large planets that acted similarly and one tiny planet that was unlike the others because it was just part of a much larger system of smaller objects.

It made perfect sense to refine our definition of what a planet was taking our new understanding into account. It's also reasonable that the job of doing that wouldn't fall to one person to decide on their own. The International Astronomical Union was already responsible for maintaining a set of astronomical naming conventions from the names of stars to the names of specific planetary features like craters. Since we wanted to have a standardized distinction between planets, moons, asteroids and comets and all the other objects in space who else do you think should do that? Having a committee of experts from all over the world seems as close to an ideal as you can get.

As for the definition they settled on being "bad science", it was debated and voted on. There were alternatives proposed, but none of them won out. If somebody ever comes up with something that is clearly better, especially as we learn more about objects outside of our solar system, that option can also be considered and voted on. What other process should we have for those kinds of decisions?

> There are people who feel that it's worth classifying all the objects in our solar system and that doing so is useful.

Up to a point. Part of my point is that the specificity of the new definition of "planet" is a bit silly. It's completely arbitrary. It's certainly not uniquely correct in any sense.

It's also a kind of post-hoc definition which assumes our specific Solar System. For example, let's say you had a rocky body, around the size of Mercury, that had a very eccentric orbit that only reached the Kuiper Belt every few hundred years, at its apoapsis. Would this object "clear its orbit"? Hard to say - the IAU definition isn't precise enough to answer this.

The IAU definition is basically the answer to the question: how do we label the closest eight planets to the Sun as planets without saying that's what we're doing, because we don't want to have to add a whole bunch of KBOs to the list of planets?

None of what the IAU did here constitutes anything resembling real science.

The term "fish" is a case in point. Traditionally, the term means a creature which lives underwater, which would include whales and dolphins, and indeed used to, despite being mammals.

It gets worse. Whales and dolphins are more closely related to certain fish than those fish are related to some other fish. (As are we by the way.) There are also some fish, such as lungfish or certain eels which can spend more time out of water than whales and dolphins can. Some fish can even breathe air, which undermines another assumption about whales etc.

For some reason, I rarely hear fewer people objecting to jellyfish or shellfish being referred to as fish, even though these are more distantly related to fish than mammals are.

So biologically, the term "fish" doesn't make much sense.

Your point is fishy. But if the IAU definition changes to "a body orbiting a star", we can rename them to "paparazzi".

That was quite funny. I think my point is that terms are not always as precise as people think they are.

As others have stated, there appears to be some kind of spectrum. Some of the inner planets have more in common with the moons of Jupiter and Saturn in some regards, than they do with Jupiter and Saturn themselves. For a start they have a surface that can be landed on. (Maybe not so much in the case of Venus or Io!!!)

Pluto's most obvious problem is that it is too similar in size to a large number of other objects. But it does have some resemblances to planets and larger moons. I'm not keen on the phrase "dwarf planet" because it makes me think of objects that are much smaller than Pluto is.

Which would make the article's subjects "weirdly aggressive nerds who are incapable of nuance, and insist that" a non-astronomical definition be used in an astronomical context.

While reading your comment it occurred to me that virtually all reporting on (or talking about) science involves applying it to an unsuitable context. Schrödinger's cat is probably the most prolific example of this.

You’ve explained something very well that I hope certain groups of people will try to internalize.

My understanding was part of the definition was changed thereby recategorizing Pluto?