This…still…?
FFS! Pluto is a FRACTION of the size of our moon.
In terms of size, Pluto is closer to being a continent than a planet…
Move on…
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The moon is big, but it doesn’t have an ocean.
I feel like the decision about how to classify planets was mostly about how many name we can expect school children to memorize.
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Naw man. We don’t want them each to find out how many others there are and unite against us. Let’s just keep the number at, like, however many…
This still, forever apparently. But note the buried lede here. Pluto keeps grabbing headlines, but the paper is really about counting the moon as a planet, along with very large numbers of other moons.
Planet has long been associated with “major body” and there’s nothing inherently wrong with wanting to keep the numbers of those around a dozen instead of a gross or more, especially when you’re the people who have to keep track of them all.
Yeah, the IAU calls the others exoplanets. It’s heliocentric but understandable…because again, their job is to keep track of the thousands of objects around the sun, while there isn’t another star where we’ve found a single moon or asteroid.
What’s ridiculous about this to me is this is an incredibly well-defined term…there are a couple ways to measure it and all of them give an order of magnitude gap between the eight big objects and the others. But hydrostatic equilibrium is not. It’s really hard to say what’s actually in hydrostatic equilibrium or nearly round. For instance, here’s Mimas:
Not going to find a more spherical object than that, are you? But guess what, if it were in perfect hydrostatic equilbrium, it wouldn’t be. It would be flattened by its rotation. It clearly was rounded out by self-gravity at some point but now it’s frozen and is holding its shape.
Round is a problem too. Here are the largest four asteroids:
Everyone agrees Ceres is round. The others…it’s tough to tell. Vesta could be considered round if you’re willing to consider it as having a large chunk blown off it. There’s no way Hygiea is big enough to be in hydrostatic equlibrium, but it looks more round to me. And, for the record, it’s not at all obvious to me why you should care, who gains by trying to draw a line between them.
This is what I hate about these “moons should be planets too” papers. At least this one doesn’t say things like “Jupiter hasn’t cleared its orbit” that show they couldn’t even be bothered to read the wikipedia article on the subject, and goes to the trouble to explain why they might use the term “planet” for a concept that primarily includes objects that were never planets. But they still keep pushing for a definition without actually doing the homework to figure out how to actually apply it.
Meanwhile, the most natural way to consider the solar system is the sun, the eight largest masses that have cleared orbits around it, other objects that orbit those, and other objects that form inner and outer belts. Take away a term for one of those and I promise you it will be replaced. 
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I think this timeline went bad the moment we dissed Pluto like we did.
Or maybe it was when we opened that black sarcophagus with the black liquid?
Either way, we can only make one of those two things right again at this point.
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The most natural way to think of the solar system is as a system with a sun, 2 gas giants, and 2 ice giants, zero hot jupiters. a (small) black hole, and a bunch of miscellaneous small bodies.
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I wouldn’t count the black hole as a given just yet, but counting everything smaller than Neptune as unworthy of categorization is definitely an approach, I’ll give it that. I wonder who it would be useful for…people looking at other stars are having a tough time picking up terrestrial worlds but are definitely interested in them.
For myself, the fact that I don’t think places like the Moon, Ceres, Io, Europa, Ganymede, Callisto, Mimas, Enceladus, Dione, Rhea, Titan, Iapetus, Miranda, Ariel, Umbriel, Titania, Oberon, Triton, Orcus, Pluto, Charon, Huya, Salacia, Varuna, Haumea, Quaoar, Makemake, Varda, Gonggong, Eris, Gǃkúnǁʼhòmdímà, Sedna, and so on should be called “planets” doesn’t mean I think they’re not interesting. I hope I’ve made it plain it’s the contrary.
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Aw… 
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Again with the: “Exoplanet is not a planet. Dwarf planet is not a planet.”
These people need basic education in how to categorize things.
Your phone/tablet is not a computer, it’s a dwarf computer.
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The industry term is fondleslab.
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I agree that dwarf planet wasn’t a great name…especially since as I pointed out the term is neither particularly well-defined nor as far as I can tell useful, and I think only was there for the sake of people worried about “demoting” Pluto too much.
But “minor planets” and “planets” have been considered distinct groups for a long time. Just like pygmy chimpanzees are a different species than true chimpanzees. And if you think that’s against how to properly use English, I have bad news for you about sea lions and jellyfish.
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At least starfish are now sea stars. Don’t tell the IAU though or they’ll want to demote them.
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You know, I think one of the biggest examples as to how disingenuously people take this whole question is that they actually consider it a “demotion”, as if it’s a case of assigning noble titles to things, instead of a recategorization in an attempt to better capture the objects in our solar system and how they relate to one another.
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How I killed Pluto occasionally brings to light the shear pettiness that can exist with the astronomical community.
I admit that in the week before the announcement, even I worried a bit about breaking the rules. I am, by nature, a rule follower. But I really wanted Dutch to be Sedna in time for the announcement. I thought it mattered—and, it turned out, based on those crayon drawings, it did. Finally I decided I would buck the rules, though politely. I called Brian Marsden, an astronomer at Harvard University who was, in my opinion, the gatekeeper of the solar system. He was the person to whom you sent the very first announcements of discoveries. He checked that your calculations were right. He put your discovery on the official list. And he was always the first to be amazed and say, “Wow! What a great discovery.” Brian was also the secretary of the Committee on Small Body Nomenclature. I told him what I was planning to do. He asked if he could tell the chair of the committee ahead of time. Of course, I said. Everyone agreed that a name was a good thing and that Sedna was a good name. To the chat group, though, I was a rule breaker in need of punishment. One particularly agitated enthusiast tried very hard to prevent me from officially naming Sedna Sedna. Before Sedna was quite eligible for an official name, he proposed, through the official channels, that an unremarkable, hitherto anonymous asteroid—which was nonetheless eligible for a name—be named Sedna, after the Inuit goddess of the sea. No two things in the solar system can have the same name, so my Sedna would have had to get a different name. “Rejected,” declared Brian Marsden. Names of important mythological figures would be used only for important astronomical objects. The enthusiast next proposed to name the unremarkable asteroid after Kathy Sedna, a Canadian singer. “Clever,” responded Brian Marsden, who, being in charge also of when things are eligible for names, quickly realized that my Sedna was now eligible and made sure the name became official.
Brown, Mike. How I Killed Pluto and Why It Had It Coming (pp. 106-107). Random House Publishing Group. Kindle Edition.
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Named after the god of the underworld if a planet, named after the cartoon dog* if a dwarf?
* who’s owned by another cartoon dog. Go figure!
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It’s somewhat ironic that Alan Stern wrote an orbit clearing criterion that relegates Pluto and Ceres to the category of “unterplanet”.
Indeed that paper seems quite aware of Pluto’s rather precarious position.
The subject of how Solar System bodies should be classified seemed easy only two decades ago. Among the small bodies, comets showed tails, and asteroids did not. Regarding the planets, there were nine: 4 terrestrials, 4 gas giants, and Pluto. The story was pretty straightforward.
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I think Ganymede and Titan have grounds for a lawsuit.
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