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> “One of the biggest flaws with the IAU definition is that you can have the same object in two different orbits,” says Kornfeld. “In one, it’s considered a planet, and in the other, it’s not considered a planet.”
No, there is no flaw in this, and moreover there is nothing new in this. This is how it has always been, it is not something invented recently.
In the Solar System, there are 3 Mercury-sized satellites and other 3 Moon-sized satellites, besides the Moon. If they had not been in their orbits as satellites, they might have very well been planets. Therefore the old definition of "planet" also depended on the orbit of the body, not only on the size and shape of the body.
Most of those satellites are bigger than Pluto. Triton, the biggest satellite of Neptune, had been in the distant past another planet with an orbit close to Pluto, but it was captured by Neptune and it has become a satellite. Otherwise it would have remained a "dwarf planet", orbiting close to Pluto. So Triton was demoted from "planet" to "satellite", by Nature, not by a human organization.
The current definition of "planets" and "dwarf planets" is fine.
If anything, there are too few planet classes, not too many. A more useful classification is into big planets, medium planets and small or dwarf planets, where the Solar system has 4 big planets, 4 medium planets, and a lot of small planets.
The big planets, i.e. which are big enough to retain the volatile chemical elements, like hydrogen and noble gases, not only the refractory elements, have a very different chemical composition from the medium planets, and this difference will also exist in any other stellar system that has condensed from gases like those at the origin of the Solar System, with more oxygen than carbon (there exists the possibility of stellar systems with a different chemical composition than the Solar System, formed by condensing from gas mixtures with more carbon than oxygen).
There’s the Vulcan planet classification system where Earth is a Class M world, but I guess that won’t be adopted until 2154.
I‘m seeing this classification for the first time, but it sounds very reasonable and feels like it should have been like that. Is it your idea or is there any story behind it?
We already have the terms "rocky planet" and "gas giant" that pretty much cover it. The only thing missing is an official IAU decision which, well, would have even less effect than the Pluto thing I'm guessing, since it would just be introducing a sub-division in the category.
Oh, right. It does exist, it is very accurate, but the names sound like LOTR party:
- a gang of dwarfs
- some rocky ones
- and gas giants
- and one star to rule them all
Many people use it, but it is not something codified formally by an international organization, like in the IAU definitions of "planet" and "dwarf planet".
Since the Moon's orbit is always concave towards the Sun, one could even argue that the Moon is a planet, not a satellite, it just happens to have an orbit that is closely coupled to that of another planet, Earth.
As I understand it, in fact, there was discussion about defining systems like Earth-Moon as double planets, but that didn't make it into the final definition.
>the Moon's orbit is always concave towards the Sun
Huh?
Here’s a visualisation https://www.youtube.com/watch?v=KBcxuM-qXec
I have heard people argue that we are in fact in a kind of binary planetary system. No other planet has such a large satellite relative to its size, until you get to the likes of Pluto etc.
The Earth is closer but I don't think there's any good argument to say it's actually a binary system. Notably the Earth-Moon barycenter stays inside the Earth, and the Sun-Jupiter barycenter doesn't stay inside the Sun. But barycenters are too easy to get outside of objects anyway.
The "battle" for Pluto is an interesting case study in indoctrination. A few generations of children grew up being taught a specific fact, saw it in textbooks, learned mnemonics about it, had memorable cartoon characters named after it, and then one day they were told – with sound reasoning and plenty of scientific evidence – that they should now update their views on the topic.
You would think this group of well educated, critically thinking adults would go "sure", but something fundamental in their brains just refuses to let them accept this meaningless change to their lives.
Now scale this up to actual impactful topics like religion, politics, relationships, race and more and most conflicts around the world start to make sense.
The thing is, there is no real evidence to back up the classification. The assignment between words and objects is arbitrary. A consistent definition for "planet" can be given and immediately after define the Solar System as being comprised of nine planets, with the understanding that a "planet" and a "planet of the Solar System" are similar but distinct concepts. The same is already done in biology with paraphyletic groups, with for example "reptiles" not including birds.
(I say this as someone who doesn't care either way whether Pluto is a planet or not.)
It's a definition. That is not a matter of scientific inquiry or fact, the definition is whatever people want it to be. You're belittling people for ignoring scientific evidence, but there's no scientific evidence to ignore, and cannot be.
Pluto was only discovered in the 1930s. The only cultural heritage of Pluto as a ‘planet’ is a few decades of science schoolbooks, but going by these comments you'd think it's been in the same list as Jupiter since the Babylonians.
Unfortunately this is both a false dichotomy fallacy and an appeal to extremes.
1. Yes, there are culturally significant things that have happened since the 1930s, including the discovery of Pluto and its designation as being a planet. In fact, in 2006 -- far more recently -- a group of people got together -- known as the IAU -- and they also performed a cultural act amongst themselves when they decided to stop calling Pluto a planet, undertaking a social process ("voting") in adopting criteria for doing so.
2. If you would rather define a planet as a wandering star that's visible to unaided humans in the night sky, I'd respect that, and I kind of like the idea. It's somewhat romantic, and it avoids the myriad issues that the article here discusses that have caused the 2006 IAU definition to start to smell bad. However, it's really none of my business. The problem comes up when you police what other people call things, not when you decide to subscribe to the IAU of your own volition.
Yeah apparently people are getting harassed on the regular about Pluto, I'm a little confused.
Uranus and Neptune don't have a long human heritage either. Neither appears to have been known to the Babylonians.
The actual problem here is weirdly aggressive nerds who are incapable of nuance, and insist that an astronomical classification (Pluto is not a planet by the IAU definition) should be used in non-astronomical contexts.
Historically and culturally, Pluto is considered a planet. An IAU classification shouldn't be used to try and retroactively change that, because the IAU does not have control over history and culture. It's a fun fact (did you know that Pluto is not classified as a planet by astronomers?) not a diktat.
Similarly, a banana is 'officially' a berry, which means that it is classified as a berry by botanists. This does not mean it is considered a berry in any other contexts. If you told someone you had made a berry crumble and it was filled with bananas, you would look strange. We have countless examples of this (often focused around food): a tomato does not belong in a fruit salad no matter what botanists say.
Different terms are used with different specificity in different settings. Language and culture and [older disciplines] are not governed by the rules of [newer disciplines or bodies]. If people with 'I love space' t-shirts would stop "um actually"-ing, no one would have a problem.
> 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.
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.
"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.
> 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.
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.
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.
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...
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.
This is what should have happened. (And it’s not too late — Pluto will remain with us for a while yet.)
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.
> 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.
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.
> 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.
> 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.
> 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.
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.
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.
My understanding was part of the definition was changed thereby recategorizing Pluto?
The obvious solution to this issue is to destroy Pluto.(*)
Many problems can be solved by application of sufficiently powerful explosives.
(*) Or, possibly, eject it from the Solar System.
The problem is that the word “planet” refers both to cultural symbols — mythology, gods, archetypes, and the heavens — and to objects of scientific study. Those are different domains, and one of them is cultural heritage, and the other is irritating when it tries to infringe on the first one.
There’s no need for a god complex. Stop picking and choosing which planets are real. Scientists can create their own, more precise words for things. Planets are sacred. Things that clear their orbits are not.
You can’t subdue the public into giving up their gods out of difference to science — you’re just losing people.
I think not quite, although many planets have the names of the gods. They called them planets due to their motion, so it is still called that. The use of the same word in different contexts can have different usages and different (but sometimes related) meanings. "Planet" is used differently in astrology than it is in science (astronomy); this isn't a contradiction (although, like any words, can sometimes result in confusion if you do not make the meaning clearly).
> “One of the biggest flaws with the IAU definition is that you can have the same object in two different orbits,” says Kornfeld. “In one, it’s considered a planet, and in the other, it’s not considered a planet.”
So… planet Ganymede when? Or Titan?
The main objection to calling Pluto a planet appears to be that if Pluto is a planet then up to about 200 other objects should also be called planets, that the list would be of unknown size and regularly changing.
That's an objection? No, that's a benefit! I think it'd be awesome to be regularly discovering new planets.
That's sort of what bothered me the most at the time. It seemed like the argument was that it was "emotional" or something to keep Pluto a planet when there might be so many of them. But I never understood why it was less "emotional" to insist that a planet be a certain size or that there should be a certain number of planets.
"Discovering new planets" only has the cachet it does because there are so few of them, and they are individually so significant. It would quickly lose that significance if there were hundreds of them. To be precise, it would acquire exactly the significance it actually deserves, but having diluted the meaning of "planet" as applied to the big eight in the process. We would soon want another name for the originals to compensate.
We can still be reasonably excited about discovering new things in the solar system without pretending they're in the same category as Earth and Neptune.
You know, this is really just a fantastic opportunity to realize the phenomenal psychological power of "headcanon". Who cares if Pluto is or is not tagged with the word "planet" by some organization you know effectively nothing about, have no control over, has no control over you, and couldn't so much as move a pebble on the planetary body in question any time in the next 20 years, if not more?
Have whatever emotional relationship you like with "Pluto" and don't wait around for others to validate it. It's fine. Nobody can stop you. I'm a bit fond of Ceres myself. Nobody can stop me. Nobody needs to approve it. Take control. Write your own headcanon.
I agree, call whatever you like whatever you want. Just don't expect schools to teach that to anyone else. We get enough of that from the folks who want to replace science class with "God did it".
who did do it?
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In case anyone was curious, the Moon is bigger than Pluto. Pluto's 2/3 the size of the Moon. If any dwarf planet should be upgraded to a planet, it's Eris. Eris's diameter is over 600km bigger than Pluto's.
Because the IAU does not uniquely hold claim to undeniable, universal, transcendent truth that should be received without question or doubt -- or even healthy scientific disagreement -- alternate planetary definitions exist. In at least one of them, both Pluto and the Moon are planets.
Pluto's diameter is 2376.6±1.6 km, while Eris' diameter is 2326±12 km. Perhaps you're thinking of mass instead of size?
Aye, but what does Pluto orbit, and what does the Moon orbit?
In order to be defined as a planet, an object needs to meet 3 criteria:
- Orbits a star (Pluto does and I assume that's what you were asking about)
- The object has enough mass to pull itself into a sphere (meets this criteria)
- The object has enough gravity to have cleared its nearby orbit of debris and other objects
Neither Pluto nor Eris qualify for a planet because of that last one and, like I mentioned, the Moon has more mass than Pluto and Eris. The Kuiper belt objects all have this issue, but my point was that dwarf planets are pretty small - especially compared to other objects around Sol. If you walked non-stop around the Moon it would take 91 days compared to Pluto's 62 days and Eris's 61 days.
The designation of dwarf planet is not that big of a deal imo.
Pluto orbits center of combined masses of itself and Charon, which does not lie within either of them. Also, they are both tidally locked to each other, just like Moon is tidally locked to Earth.
My favorite nonfiction book in years is "Storia della pasta in dieci piatti" by Luca Cesari. The signature chapter explores the day in 2015 when celebrity chef Carlo Cracco stated on television that a clove of garlic is an ingredient that can go into amatriciana. Cesari explores the absurdity of the resulting uproar, given the actual history of the dish.
People like to make rules. Leave them be in their tree houses, unless you really like to play too. I thought it was a right of passage in high school to laugh at the French forming committees to tell peasants how to speak their native language. We haven't generalized from this example?
Who gives a rat's ass whether this governing body thinks Pluto is a planet or not?
This is hardly on par in terms of stupidity, but one thing you learn from flat-earthers is that humans love disagreeing with a consensus. Nothing make a certain type of person feel smarter than disagreeing with everyone. If you say the sky is blue I'm going to say it's green because I'm so smart.
>If you say the sky is blue I'm going to say it's green because I'm so smart.
Flat-earthers are definitely wrong about the shape of the earth, but even they admit the sky is blue, assuming they aren't afflicted with some unfortunate variety of colorblindness.
In my observations of flat-earthers, they're people who reject the consensus surrounding a particular fact because they haven't observed that fact for themselves, which doesn't make them bad people or even crazy. I do rather enjoy their attempts to measure basic scientific facts about the earth, such as when a group of flat-earthers used lasers and the ocean to measure if the earth indeed has curvature. When the evidence incontrovertibly showed the earth indeed has sufficient curvature to match the scientific consensus, many participants were quite shocked. As long as they adjusted to the consensus, or even hypothesized another theory they felt worth testing, they're not crazy, just skeptical of authority.
But how could you be alive and not have observed that the earth is curved? Why does a mountain, building or ship disappear over the horizon if the earth is not curved? That alone should be sufficient evidence to believe that the scientific consensus on this is likely to be true.
I have not observed directly that a human will die after 3 days without water but having experienced thirst & dehydration in limited amounts, I have no reason to doubt that is likely the case.
That's what I don't understand supposed "rational" flat earthers. It's fine and somewhat rational to be skeptical of authority but when the contrary idea takes enormous leaps of faith to consider, it seems weird to me to believe something for the sake of it.
>But how could you be alive and not have observed that the earth is curved?
I know someone who is almost 40 years old that has never left his hometown. He's a reasonable person who holds gainful employment, but from our conversations, he's never been in a skyscraper, flown on an airplane, taken a road trip into the mountains, or even hiked up a large hill, for that matter. He also lives in a land-locked city, so he's never seen the ocean. As such, he has never directly observed the earth to be curved. With all due respect, many people like him do exist in the world, and perhaps you're not acquainted with people like him.
However, he is not a flat-earther because he spends much time on the Internet reading about the way the world works outside his hometown. Basically, he believes in the truthfulness of large institutions, which really is why you and I believe the earth is round; that is, we haven't actually performed a bona fide experiment (not just going in an airplane or up a mountain) to measure the curvature of the earth for ourselves, but we trust the results of those who have, and we also accept that certain technologies like GPS as it is currently implemented can only work if the earth is round (not just in satellite orbits but also the slight-but-critical relativistic shift from a geosynchronous satellite).
>when the contrary idea takes enormous leaps of faith to consider, it seems weird to me to believe something for the sake of it.
That's cool, but many people are capable of believing in something for the sake of it. One fact that stands out to me is that we all use some amount of faith to accept that the earth is round, though perhaps not quite a leap's worth.
They are absolutely crazy. There is no defending it. It is something that makes stupid people feel smart. There are easy, verifiable experiments that can be done and they refuse to accept the outcome.
Have you ever called someone crazy, only for them to stop dead in their tracks and say, "wow, you're completely right, how could I have been so blind?"
I haven't, and you probably haven't, though if you have, I'd love to hear that story. As I said, they're skeptical of authority and need to run the experiment themselves; some will even flip on flat-earthers who run the experiment and change their minds. Only those who perform the experiment and still refuse to accept the outcome are deserving of being left to their own crazed devices. Until then, they're just ignorant and/or weird.
As fare as I'm concerned, Pluto is a planet. I've got a hand-written note from Clyde Tombaugh that says so. Back in the mid-1990s, a year or two before he died, I write him asking about some astronomers who were starting to question it.
I'm in the same camp. I believe the classification of Pluto as a dwarf planet was arbitrary and inconsistent. I mean, it's been known as a planet for almost 80 years and suddenly we demote it?
I believe someone was trying to make a name for themselves here and ignoring the history of Pluto and its discovery.
I'm on team Pluto here but no, the problem was that Mike Brown found like a dozen 'planets' and no one wanted to deal with that. It was closer to preventing someone from making a name for themselves.
We could simply define Pluto as the edge of our Solar System and everything beyond its orbit a Kuiper Belt Object. There's nothing wrong with that.
Why bother coming up with a pseudo-scientific requirements list for planets when these don't work for a large number of cases.
> We could simply define Pluto as the edge of our Solar System and everything beyond its orbit a Kuiper Belt Object. There's nothing wrong with that.
There is because Pluto is inside the Kuiper Belt and just as much a part of it as all the other "planets" in there. There's nothing wrong with defining our solar system as having 8 planets plus a bunch of other stuff.
That would include Ceres, Quaoar and Orcus as planets.
It's really hard to come up with a definition of a planet that includes Pluto but doesn't include Orcus. Orcus is very close to a mirror of Pluto that is 120 degrees out of phase. Even in name: Orcus is the Roman name for the Greek god Pluto.
What part of "we define it so" did you not understand?!
The three I listed are inside Pluto's orbit. Part of the time for the latter 2.
If you want to say that Pluto is a planet for historical reasons, that's fine. Just don't try to invent pseudo-scientific nonsense to justify it at the same time you are decrying psuedo-scientific nonsense.
> We could simply define Pluto as the edge of our Solar System and everything beyond its orbit a Kuiper Belt Object.
A Kuiper Belt Object not being a part of Solar System doesn't make any sense. A star system is the star + all objects that orbit it. Why would you arbitrarily exclude some objects that orbit the Sun?
It was fine and dandy until Eris came along.
Eris is bigger than Pluto, so if Pluto’s a planet then so is Eris. So you have 10 planets.
And then how many other Erises are still hiding? How many planets do we have then? It must be some very large unknown number!
Holding the true number of planets to be a large unknown number was anathema to many.
The demotion of Pluto was primarily motivated by a desire for the word “planet” to refer to a fixed, never-changing number of large bodies orbiting the sun.
The issue is that when we discovered Pluto we thought it was much bigger than it turned out to be. If it was as big as they thought then sure it would be a planet. As it is it isn’t even the most massive dwarf planet
They saw a problem with the discovery of other Kuiper Belt Objects and came up with a pseudo-scientific definition to "solve" the discrepancy.
> pseudo-scientific definition
How is it pseudo-scientific?
Or alternatively, how would any conceivable definition not be equally "psuedo-scientific"? There isn't going to be a bright, shining line. Our own Solar System is complicated enough and if we could see out into the cosmos with equal detail the lines would get even fuzzier. Judgment calls are inevitable.
How to keep Pluto as a planet but say larger objects than it that also orbit the sun aren't planets, is the question I guess?
Literally say Pluto is a planet through the collective statements of parties involved.
This is like when English professors gripe about word usage in books. That's wrong, you can't do that. Then society at large does it and it becomes correct usage. We define our world.
It's basically a question of definition: we define Pluto as a planet and the others as Kuiper Belt Objects (KBO)
As human beings we're allowed to make these kind of decisions. We define ourselves to be outside of the animal kingdom when we're clearly part of it and a type of animal ourselves.
The question would be what are the specific rules that lead to that, and how you'd apply those rules outside of our own solar system. Any rule that just calls those distant objects KBOs is specific to our own solar system which is a silly rule to be making in a world where we already knew about hundreds of exoplanets.
The question at hand is "how do we define a planet" from a universal standpoint, because it hadn't really been defined beyond an "I know it when I see it" level and that was becoming a problem.
Objective rules that do not assume you're talking about our solar system are key here, and the serious proposals basically come down to 8 planets or dozens and growing, and from a practical standpoint the former was the obvious choice IMO since all it really affects is what gets focused on in general education environments.
If you just want to make an arbitrary decision that these things are planets because you want them to be as opposed to because they meet certain criteria, that's not useful to anyone.
If you must insist on squaring the circle:
Pluto is the Princeps of Kuiper Belt Objects, the First Among Equals. It is the most honored KBO, even if it is not a planet.
But why? There is no reason to care about the classification of Pluto. Why don't you just define that you're okay with it not being a planet?
My Very Educated Mother Just Served Us Nine...uhhhm... !?
Mary's Violet Eyes Make John Stay Up Nights.
still works, how bout that?
Nachos. She served us nachos.
The problem with demoting it lies in its beauty. Pluto is beautiful and interesting. We want it to be important. But instead of being the "last of the planets", maybe instead it should be the first of the dwarf planets.
> someone was trying to make a name for themselves
100%
Scientists try to coin new terms all the time. It’s great for the researcher if people actually use it. But why do that when you can just sign your name on a term everyone already uses?
Redefining “planet,” from the 9 culturally accepted symbols into something else, was a swindle. “Things that clear their orbits” could have been TTCTOs. It happens all the time, coining precise terms for things. Why should this one have been any different? The public was right to push back and to protect their mythology.
A swindle, really? Who got cheated out of money?
The asset lost in this in this case is from the commons. That is, the ability to say "the ninth planet" or "the planet Pluto" without incurring smug harassment from legions who probably couldn't explain what the IAU is.
Rather ironic to complain about redefining a word by abusing another word beyond recognition.
It’s completely unsurprising to deal with grammar policing over substance, but…
In terms of financial motives, I would reason that a motive for extending the term “planet” to cover the innumerable large objects orbiting other stars would have been as a better sales pitch to Congress. Studying “planets” lightyears away was a sort of brand hack which would have driven more funding. And when the “planets” was established as comprising a virtually infinite set, rather than simply a list of 9 known objects, the nomenclature collapsed in its usefulness, which is why the IAU started looking for a way out of its own hole.
However, as the article here discusses, the IAU’s approach has pretty much failed. It doesn’t hold up to scrutiny as a thing that’s meant to be usefully applied. How exactly do you confirm that all of those exoplanets have actually cleared their neighborhoods, or is the truth that it never actually mattered to anyone in the field?
Have any scientists or agencies written papers or reported to Congress that they discovered or studied some exoplanet — using public funds — when in fact they had no way of confirming whether its neighborhood was cleared? It sounds completely improper to me, but the reality is that it never really mattered.
Sorry, but how does using “swindle” in a way that’s completely divorced from how it’s normally used qualify as “grammar policing,” but comparing a small change to a scientific definition to a crime is somehow reasonable? Financial motives? Get a grip, man.
If you certify that you have discovered an exoplanet and you do not know whether it has cleared its neighborhood, that may be a crime under the IAU’s definition. Possibly a financial crime if research funding was involved. I’m not a lawyer, just someone who can spot a charade every now and then. My guess is the IAU would say, given the challenge, “ah, well of course we didn’t mean for our universal definition for planets to be applied outside of the Solar System!”
Edit: Because we’ve apparently reached the end of how long an hn thread can go, replying here, yes, of course nobody cares about this, that’s why it’s absurd to expect other people to follow it and to shame them when they don’t. Be nice or don’t be surprised when the general public votes to cut your scientific research funding or won’t accept important advice from experts.
This seems like the least important issue in the world to keep complaining about.
Deciding the color of the bike shed is easier than making important decisions about the building it sits next to. It's a well-known phenomenon https://en.wikipedia.org/wiki/Law_of_triviality
[Edited for clarity.]
My issue with the IAU's definition is that the body must "orbit the Sun". I would prefer they said "star" instead, and excluded other stars (so a binary star means neither star is a planet).
If the IAU had any sense they would have made Ceres a planet instead of axing Pluto. These decisions should be made in a way that makes funding exploratory missions as easy to sell as possible. Pluto the planet wis easier to sneak through congressional budgets than Pluto the Dwarf planet. Instead of waxing poetic on the Platonic form of planet, just draw a wide line around things people want to get probes sent too without going so broad as to lose the plot. Even better would have been to give Pluto a designation like the nearest Rim Planet, implying there are so many strange Rim Worlds for us to find and explore.
Could someone explain what the IAU means by "clearing its orbit". For example, could we consider the Earth having not "cleared its orbit" because of the Moon? The Sun attracts the Moon more strongly that Earth does, so does that mean that the Earth doesn't fit the criteria? Or does the IAU have some sort exception for moons which they've defined some place else? I'd really appreciate if someone with more knowledge could explain.
> Could someone explain what the IAU means by "clearing its orbit".
To use a different phrase from wikipedia, "orbital dominance".
Other objects that stick around are either captured as satellites or forced into resonant orbits.
> The Sun attracts the Moon more strongly that Earth does, so does that mean that the Earth doesn't fit the criteria?
The Earth's sphere of influence goes out to about a million km, 2.5x the moon's orbit.
Classification is a human invention… are tomatoes, cucumbers and zucchinis fruit or veggies? Non issue.
In science, classification should have some predictive value. You should be able to predict the characteristics or behaviour of a class member based on its classification. For example if you classify something as a fruit you could predict that its seeds should be on the inside.
Classifying Pluto as a planet is problematic because it lacks the behaviour and characteristics of something that formed according to theories of how planets form. If you tried to describe what a planet should look like based on the nebula hypothesis, you would not be describing Pluto.
Instead it has behaviour and characteristics a lot like the many trans-Neptunian objects, so it makes more sense to classify it that way.
OMG, I was taught there was 9 planets my whole life. I had no idea there is now 8 planets in the solar system. My very educated mother just sold nine....
It's dumb, but whenever I see something representing the planets, I always count them. Occasionally you come across places that still include Pluto.
Most recent example I found was the Swatch MoonSwatch Collection [1], which includes the Sun, Moon, eight planets and Pluto[2].
1. https://www.swatch.com/en-us/bioceramic-moonswatch-collectio...
2. https://www.swatch.com/en-us/mission-to-pluto-so33m101/SO33M...
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"How I Killed Pluto and Why It Had It Coming" - awesome title for an Astronomy book
The claim that the IAU vote was procedurally invalid is interesting
> Pluto represents the underdog ...
I see what Schindler did there!
Back in school I learned the acronym:
My Very Easy Method Just Speeds Up Naming Planets
And it was so convenient! Does anyone know a good alternate now that the P is gone?
> Does anyone know a good alternate now that the P is gone?
My Very Easy Method Just Speeds Up Naming
I think of them more as by properties: Mercury hasn't even an atmosphere, it's too close to the sun; Venus is a hot earth so it sits closer than us; then comes its sister planet Earth; Mars is cool by comparison and sits further away than we do. Jupiter and Saturn are harder but sit before the ice giants Uranus and Neptune, again making logical sense. Whether Jupiter or Saturn comes first, I guess there's some memorisation, with or without some sentence about it
Back in my day, we had nine planets.
We still have nine planets. The IAU has no power to tell me what to classify things as.
I truly don't get why people have so much reverence for Pluto. And, unlike something like "fruit," which has a botanical and culinary definition which serve different purposes, I really don't get why anyone would care about the non-scientific definition of planet. Maybe I'm just ignorant here: what's the cultural significance of some celestial object being considered a planet?
Let the experts decide same with any other field.
The correct planet criteria are, IMHO:
- not a star
- not orbiting a planet
- roundish
- greater than 1000km radius
That would restore Pluto to its rightful place and add Eris.
Why 1000 km radius? I know that 1000k diameter might be important for cold bodies to keep their equilibrium, but what does 1000km radius give?
Because honestly anybody who played stuff like KSP RSS or any space game taking place in our solar system represented at scale with adequat orbit weirdness probably told themselves "that's Pluto? Ok i get it, not a planet".
It's just a nice round number to use as a clear boundary.
It's time to give it up. Nobody wants there to be 23 planets...
It seems as though Pluto's primary problem is "clearing the neighbourhood." Given Pluto's orbit travels closer and further from the sun than Neptune, does Neptune also have the neighborhood clearing problem since it has not cleared Pluto?
In celestial mechanics, "clearing the neighbourhood" (or dynamical dominance)
around a celestial body's orbit describes the body becoming gravitationally
dominant such that there are no other bodies of comparable size other than
its natural satellites or those otherwise under its gravitational influence.[0]
Trans-neptunian objects, including Pluto, are in orbital resonance. They owe their stable orbits to the existence of Neptune.
It’s like saying Jupiter is not a planet because the Trojans exist.
...or like saying Earth is not a planet because NEA's share our orbit.
If you have to argue that it doesn't apply to Jupiter or Earth because they are obviously planets, it implies that "clearing the neighbourhood" is a vague and not particularly useful criteria.
[delayed]
Except I said nothing of the sort. I said the opposite.
Jupiter, Neptune and earth in your example dominate the gravity of their orbit by locking the smaller bodies into orbital reasonances.
It’s not a vague criterium. It might be an irrelevant one if you are interested in geophysics, but it’s concrete and testable.
> other bodies of comparable size
In addition to what other commenters said about orbital resonance: Neptune has approximately 20 times bigger radius and is about 10_000 (ten thousand) times heavier. This is comparable to difference in mass between a human and a hummingbird. Could we really call them "comparable size"? I'm not sure, this is not a particularly precise term, but I would say - no.
The "Criteria" section of that article clarifies the question. Neptune holds Pluto in an orbital resonance, which qualifies as Neptune gravitationally dominating its neighborhood. Perfect, 100% clearance is not expected anyway, since that's basically impossible in a real, dirty world where things move around.
Bring back Pluto!
As the article explains, if you bring back Pluto you must include Eris too, and perhaps Makemake and Haumea if you ignore is not as round as expected, and who know how many other undiscovered small object near them. (And Ceres? I like Ceres.)
Anyway, 9 is not an option, you must choose 8 or 10+.
Pluto is grandfathered in through the collective Consciousness of society. Just treat it the same way as tomatoes, which are officially fruits but no child believes that crap.
I'm on board with all the dwarf planets. MVEMCJSUNPHME should be easy to make a mnemonic.
no you don't. just because some nerds say it doesn't make it true. just bring back pluto and nothing else
Science works on logical rules.
What logical rule would you propose that allows Pluto to be a planet without also bringing in a bunch of others?
If you just want to arbitrarily declare things are they way you like them to be, religion is over there.
>What logical rule would you propose that allows Pluto to be a planet without also bringing in a bunch of others?
The rule would be: pluto is a planet, stay mad nerds
It’s still there. Where it always was.
Humanity's need to categorize things never ceases to amaze me.
Is it Art? It's not Art! Are bananas a vegetable or a fruit? Pluto definitely is a planet! No it's not!
Jesus, what a waste of energy.
Are we just realizing that asteroids come in all sizes? Do we really need a sharp boundary between those we call planets and those we don't call planets?
Can we consider planethood a spectrum? Like should we REALLY care if someone says there are 9 planets in the solar system, and the next person says 8?
We used to say there were 3 oceans, now there are 5. In reality, there's just one big saltwater lake. Do people fight about where one ocean ends and where the next one starts?
Let them call pluto a planet if they want, let them call pluto a kuiper object.
We shouldn't give a fuck.
Pluto as one of the outer Canadian planets in the Canadian solar system, which as you now know is part of the Canadian Galaxy is realy such a trifling concern back on one of the Canadian Continents that contains Canada proper the center of Universal Canada, but since there is dissent on it's status something can be done through a referendum.
go ahead,laugh, but wait till google AND wikipedia both come on board
It's been renamed to Planet America, thank you for your attention on this matter.
Pluto is a planet.