At that point there was no general term though. The nine planets that everyone learned was rooted in what was known for decades to be a fundamental misunderstanding of Pluto. Once they started discovering other Kuiper belt objects, they had the choice between crossing it off the list, or coming up with a criterion for which of the dozens more counted as planets (and as I have pointed out, nobody has actually quite done that yet, let alone explain why their cut off is a more meaningful one).
They could I suppose have simply abandoned the word planet altogether and replaced it with some more technical jargon. Usually people prefer scientists not do that though?
i’m certain there are instances where a refined specialized word has been chosen to reduce confusion with an existing general word; maybe after my morning coffee a few will spring to mind.
part of the point of naming, after all, is to reduce confusion and conflict.
( i don’t really care either way. i just see a simple way out of a debate that will otherwise go on for … i dunno… at least another 50-100 years )
(eta: it occurs to me adding an adjective would have been even better than a completely new name.
for example: define a “standard planet” – most scientists, in papers, wouldn’t bother with the “standard” prefix except when needing to be precise when talking about our own solar system. and everyone else would be happy with the nine they know. )
Personally I find the proposed definition in this article to be pretty persuasive:
Boom! A nice round metric number, just like the Karman line! So simple and unambiguous! Yeah, it’s somewhat arbitrary just like the “edge of space” definition but that doesn’t make it meaningless. Benefits include that we would get 10 known planets and we wouldn’t have to worry about weird philosophical questions like “just how much farther would the earth have to be moved away from the sun before it ceased to meet the definition of a planet?” (Those “clearing the neighborhood” formulas that you were pointing to would give three answers to that question)
And for anyone complaining about serious Pluto discussions getting hijacked by a dumb, uninformed “it should be a planet” debate, that’s absolutely NOT what happened here. The article and subsequent discussion started with the entirely unconsequential, unscientific naming of it and, if anything, got hijacked by serious science-minded people.
I know, but it happens enough times for me to already be sick of it, and you still see the same disdain for scientists in it.
And 1000 km is a number that’s nice, round, but has no real significance. Why that should be better than a robust criterion that actually relates to the nature and origin of the objects in question is beyond me. Things like “how much would the Earth have to move” always tell me people are missing the whole point – that the classification is based on the way solar systems actually work. We don’t get objects as massive as the eight in belts, and we only get less massive objects in them. “Biologists couldn’t tell if a pegasus is a bird or a mammal” is not a weakness of the classification, I would even say a strength, because they don’t exist.
I will note this is yet another person who also hasn’t gone to the trouble to understand what neighborhood clearing means, too, since he incorrectly claims Jupiter, Neptune, and Earth haven’t. But hey, at least he actually gave a cut off and didn’t forget about Eris the way the “let’s keep nine planets” people do.
If someone is taught the “nine” planets, they might just mentally view the solar system as a series of nine spheres.
“Eight planets” plus plus “Asteroids” + “Kuiper Belt” might be a better foundation for understanding the solar system.
Ultimately, if Arizona had announced Pluto as the state’s official celestial body, I don’t think anyone would mind. It would be perfectly fine, and fitting given the historical connection. But they had to call it a planet, and that will bother people.
I know the IAU has scientific, measurable standards to make the designations. I’m an astronomy fan, and followed this change closely and do understand it. But, like many standards, they also appear to be somewhat arbitrary and in this case specifically designed to exclude Pluto from the planet club.
Sure, but how dense is the Kuiper Belt, really? It and the asteroid belt certainly aren’t full of rocks a la Empire Strikes Back. According to the Encyclopedia Britannica there are an estimate 3,000-15,000 KBOs of 100km diameter or greater, so it seems pretty sparse.
How did Pluto form? Wouldn’t it be bits of dust collecting together through collisions and gravitational attraction, similar to the inner planets? Given the distances, is it reasonable to expect only one planetary object to form in a region that big? Do Kuiper Belt object orbits overlap significantly? Are they close enough that they would fling off into space when they are in (eventual) alignment?
Mars and Venus are way more massive than Mercury, and Earth is more massive than either of them. Mass and size are arbitrary criteria, which could have been lowered to include Pluto, Ceres, Eris, etc., or raised to exclude the inner planets.
As others have pointed out. What qualifies as orbit clearing? Earth has the Trojans, does that mean the orbit is cleared or not? Given the sheer size of the Kuiper Belt and the unfathomable distances involved, is it fair to say Pluto hasn’t cleared its orbit? How many million or billion years would it take for Pluto to clear its orbit? If Jupiter were in Pluto’s orbit, how long would it take to clear out the entire Kuiper Belt? Could it be done before the Sun expanded and ate the inner solar system? Pluto’s orbit is about 248 years, quite zippy on the cosmic scale, but again, how crowded is the Kuiper Belt?
Ultimately, it doesn’t matter what I think. The IAU established these criteria based on what is objectively measurable for them and which suits their specific needs. They are internally consistent and provide the necessary nomenclature to discuss astronomy.
No, I don’t like their choice, but no, I don’t think they arbitrarily made the decision. My attempt at humor was mean spirited and fell flat, and that’s on me. I understand their criteria from a layperson perspective. Still doesn’t mean I have to like it, and since I am not a professional astronomer, continuing to call Pluto a planet has no impact on my personal or professional life. My daughter, born after the schism, just rolls her eyes whenever I mention Pluto.
The IAU chose to demote Pluto, which is a very popular planet. I remember Neil deGrasse Tyson mentioning in an interview after 2006 that he was receiving hate mail from 6th graders for supporting the decision. Hate mail. From 6th graders. The decision makes sense from an astronomical sense, but that doesn’t mean the general public will like it. The Pluto debate will probably go one for another 80 - 100 years until planet Pluto people pass.
Until then there are real problems of racism, bigotry, and fascism that need to be addressed, and I want to be on and at your side as we tackle them.
It’s actually really simple. Jupiter has the Trojans, but they make up a tiny percentage of its mass. Pluto on the other hand is a very small portion of the mass even in its region of the Kuiper belt, which includes a lot of other plutinos, not to mention that it crosses past Neptune. That’s what makes it a belt – it’s composed of a lot of little objects with no single one dominating.
It drives me crazy that this keeps being claimed as if it were confusing even though it’s completely straightforward. The eight biggest masses have nothing of comparable size near them. All the smaller masses either orbit them, occur in belts, or have been ejected somewhere. It’s all well and good to say sizes and masses are arbitrary…and yet here they picked the one place there is actually a real cut off between two categories.
That’s not something that happened by chance either. Sure, Pluto and Haumea and Quaoar and Triton and all their fellows would have formed by accretion up to the size of planetesimals or so, but then the process stopped there. Where Mercury and Mars had a phase after that where they kept growing until all the material in their region had been used up. It’s not as simple as everything forming the way it is now, and there used to be other objects like Theia that got lost, but even so there is a real reason to consider them different. To the point where if that’s not what “planet” meant I would probably ditch it for another term that did.
On the other hand…
…there is this. The idea because Pluto was popular it shouldn’t have been “demoted”. Was it an insult to mushrooms when biologists decided they didn’t belong with the plants? And yet here this keeps being taken as if it were a question of nobility instead of trying to reflect the world around us. A good description of the solar system isn’t what counts, what counts is respecting America’s favorite, which is somehow not done unless you throw it in with objects it is not like.
You mention real problems…well, I would say anti-intellectualism and hatred of science are part of those. Sure, this particular case isn’t nearly as serious as global warming denial or anti-vaccines or race pseudoscience. But when you talk about schoolkids writing hate mail because they don’t like what scientists said, maybe instead of treating that as if it meant something was dubious about the decision, you should consider what the hell went wrong that the public would react to astronomy that way.
Because to me it looks like the same entitled ignorance as those other problems. How dare anyone let facts or understanding get in the way of what I want to be true. And I’m not inclined to give that a pass just because this time it stopped with hate mail instead of actually getting people killed.
