Talk:Dwarf planet

Featured article status
This is an old FA promotion, and does not seem to have kept up over the succeeding decade. There are a couple of unsourced paragraphs and other unsourced text, and the prose in many areas has short paragraphs and small sections. Some areas appear not to have received a comprehensive update since early FA. The History of the Concept section is mostly based on 2006/2008 sources, many of which are news or magazine articles rather than higher quality sources which are certainly available. Updates since then are restricted to a brief couple of sentences, which seems insufficient (and is partially sourced to twitter). The Exploration section is paltry, it is where I would expect to find for example an explanation of the reasoning that led to the sentence "Ceres is close to equilibrium, but some gravitational anomalies remain unexplained", which is cited to a Dawn paper. The overall structure of the article has some oddities, why is "Contention regarding the reclassification of Pluto" a separate section so far away from the History of the concept section? The pie charts are causing some image sandwiching, and seem a really odd way to present that data. The source formatting needs some tightening: there's a bare url, and others lack page numbers and access-dates. Others may find more missing areas, it does feel an oddly short article for the scope involved. CMD (talk) 03:52, 14 August 2021 (UTC)


 * Yeah, it definitely needs work. Not sure I'd have the time this week. — kwami (talk) 15:17, 14 August 2021 (UTC)


 * The "Contention regarding the reclassification of Pluto" isn't even there and aside from a couple of oblique mentions there is no discussion over the controversy regarding the definition of "dwarf planet" and or issues with the definition used, a continuing issue (note the last paragraph of the first section). Science demands a record with context and debate, but this article seems like it was edited by someone with an overzealous interest in burying even the idea of dissent. 216.115.235.42 (talk) 14:57, 26 April 2022 (UTC)
 * The issue is discussed in Definition of planet.  Serendi pod ous  15:25, 26 April 2022 (UTC)
 * I am circling back to this discussion because I see that there are still uncited passages in the article. Has the necessary updates been made yet? If not, is anyone interested in working on this article, or would someone like to nominate this to WP:FAR? Z1720 (talk) 03:07, 21 December 2023 (UTC)
 * Significant work was put into this article following my comment above, much by Kwami. Better to raise/tag any individual issues with a fresh look, rather than going into FAR. CMD (talk) 08:02, 21 December 2023 (UTC)

Dwarf Planet
Dwarf planets should only be recognized by the IAU right? — Preceding unsigned comment added by Zachbarbo (talk • contribs) 19:38, 9 November 2021 (UTC)


 * No. That's not the IAU's job. Dwarf planets are objects which meet the definition of a dwarf planet. — kwami (talk) 22:38, 9 November 2021 (UTC)
 * Corect I agree 112.134.152.33 (talk) 16:11, 19 May 2024 (UTC)

Size
What is the maximum size of a dwarf planet? — Preceding unsigned comment added by Zachbarbo (talk • contribs) 02:06, 12 November 2021 (UTC)
 * No maximum. An object as large as Mars or even Earth could be a DP if it hasn't cleared its orbit. — kwami (talk) 23:40, 12 November 2021 (UTC)

What about giant planets like the gas giants and ice giants? — Preceding unsigned comment added by Zachbarbo (talk • contribs) 13:40, 13 November 2021 (UTC)
 * Sure. A Jupiter-sized object in the outer Oort cloud would be a dwarf planet. On the other hand, a Pluto-mass object in Mercury's orbit would be a full-fledged planet. (I say Pluto-mass because Pluto itself in Mercury's orbit would turn into the most spectacular comet ever seen.) The upper limit is about dominance, not size. Double sharp (talk) 14:36, 13 November 2021 (UTC)

The definition was created for the bodies we know about. There's an obvious division between the giant planets and the terrestrials, but Venus and Mars have to be planets, so the IAU couldn't draw the line there. The next obvious division is between the terrestrials and Eris/Pluto/Ceres, and that's what the IAU chose and what their definition is meant to enshrine. They could've just said "the big eight", but that wouldn't sound very scientific. It's doubtful the IAU definition will work well for other planetary systems, though, and it doesn't work for the early history of even our system.

The next obvious place to draw a line is between planemos and SSSB's, and that was the competing definition of "planet" that was considered by the IAU. And the one that's used by people like Stern and Grundy. But in practice that's a very difficult definition to apply, because we just don't have enough evidence to tell which bodies are planemos. So the IAU definition is practical, whether one agrees with it or not, as long as we don't discover an Earth-sized body in the outer Solar system that throws everything into chaos again the way the discovery of Eris did.

I suspect that if we find an Earth-sized body that is technically a DP, then the IAU will revisit their definition of "planet" and modify it so that the new body counts as a planet. After all, technically Mercury is a SSSB, but everyone ignores that and calls it a planet anyway. — kwami (talk) 21:07, 13 November 2021 (UTC)
 * And presumably dynamicists would ignore such a definition or pay lip-service to it the way they used to do to Pluto: call it a planet and then exclude it from their integrations.
 * I really wonder what would happen if even a Mercury-sized TNO was discovered, though. Double sharp (talk) 22:39, 13 November 2021 (UTC)

Dwarves are supposed to be small. — Preceding unsigned comment added by Zachbarbo (talk • contribs) 01:15, 14 November 2021 (UTC)
 * Yes, the terminology is a little unfortunate and makes it look like the distinction is about size, when it's really about dominance. But you could always use the old term "planetoid": something that's like a planet but isn't a planet. Double sharp (talk) 11:01, 14 November 2021 (UTC)
 * Actually, I think Zach may be right. They are supposed to be small. But the IAU rejected a size limit to define planets (e.g. "Pluto or larger") as arbitrary, so they needed some other way to say the same thing that looked more scientific. They chose orbital dominance. But I wonder how important the dynamic aspect really was, or if it was just convenient. Though it makes sense of course if you're working on the Nice Model.
 * As long as we don't discover anything significantly larger than Pluto, I think we're fine. But if we find things that start filling in the planet-DP gap, it might become an issue again. — kwami (talk) 13:34, 14 November 2021 (UTC)
 * Mike Brown talked about this in this 2011 talk from about 62 minutes onwards. He thought then that some of the largest inner Oort cloud objects (Sedna's population) would be Mercury- or Mars-sized, though he used a power-law argument and based it on a size of Sedna that we now know to be too big. He thought that the debate would reopen again when something like that was discovered, and that he didn't care if people widened the definition of "planet", but also said that he thought it was important to make it really clear that there's a difference between dominant and non-dominant objects and that a Mars-sized inner Oort cloud object would not be dominant. I agree wholeheartedly with his position. :D
 * So maybe the best answer to the OP's questions is: "The current definition of a dwarf planet focuses only on dominance. Consequently there is no upper size limit, and if we take it by the letter, Jupiter would be a dwarf planet if it were orbiting in the outer Oort cloud. However, we agree with Mike Brown that the definition would be reexamined if anything like that were ever discovered, so we should not take that too seriously at the moment." Double sharp (talk) 14:32, 14 November 2021 (UTC)

Recognition
Will the IAU officially recognize Gonggong, Quaoar, Orcus, and Sedna as dwarf planets? — Preceding unsigned comment added by Zachbarbo (talk • contribs) 14:19, 12 November 2021 (UTC)
 * Doubt it. That's not their job, and if they did, they'd be engaging in pseudoscience. There might be some announcement in the future that refers to one or another of those bodies as DPs, but highly doubtful that they'll try to substitute science with their authority by making an official declaration of fact. — kwami (talk) 23:39, 12 November 2021 (UTC)
 * Tancredi advised the IAU to accept Quaoar, Orcus, and Sedna as "official" "dwarf planets" (his quotes!) back in 2010. (Gonggong had only recently been announced back then, so it wasn't considered.) They didn't respond then, so it's not likely they'll respond eleven years later. Double sharp (talk) 23:50, 12 November 2021 (UTC)


 * The IAU already substituted science with their authority in 2006 by declaring that Pluto (and Ceres and Eris) allegedly aren't planets. 2001:4BC9:A44:18BA:A5B5:96D5:BA04:477B (talk) 17:18, 10 August 2022 (UTC)
 * Dynamically, Pluto, Eris, and all others are very clearly a distinct type of object compared to the "big 8," and there is effectively zero dispute within the astronomical (not planetary science!) community regarding Pluto's reclassification. ArkHyena (talk) 08:45, 22 June 2024 (UTC)

IAU Division F report refers to Quaoar as a "dwarf planet"
Quote from the 2022 IAU Division F report : "Unexpected ring discovered around dwarf planet Quaoar. A kind of revolution has recently appeared in the field: another Kuiper belt object, Quaoar, hosts also a dense arc embedded in a continuous thinner ring, but that system lies outside Quaoar’s Roche lobe and thus should theoretically not exist. (p 2)"

"An unexpected ring was discovered around dwarf planet Quaoar (p 5)"

Nrco0e (talk) 23:23, 6 December 2023 (UTC)
 * Cool! I've added mention of this in some places. Double sharp (talk) 11:25, 8 December 2023 (UTC)
 * This might interest you. :) Double sharp (talk) 11:42, 8 December 2023 (UTC)
 * Thanks. The fact that the IAU itself is using that wording should put to rest the idea of "official" dwarf planets. — kwami (talk) 21:18, 8 December 2023 (UTC)