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Per definition a dwarf planet is:

a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape1, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

The Wikipedia page for 225088 Gonggong, former 2007 OR10 states three possibilities for its dimensions:

  • 1535+75−225 km
  • 1280+210−210 km
  • 1200+300−200 km

Which is all minimum 1000km in diameter. So how can you still doubt the hydrostatic equilibrium for such a large body?

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  • $\begingroup$ I think your Wikipedia link answers the question - that researchers agree it is probably a dwarf planet. Or is your question more about the process to get it officially recognised as one? $\endgroup$
    – Andy
    May 17, 2016 at 7:22
  • $\begingroup$ I just don't understand the remaining problem? Why should it not be a dwarf planet? What are the remaining doubts? $\endgroup$
    – rubo77
    May 17, 2016 at 7:45
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    $\begingroup$ I would guess it just needs to be recognised by some committee somewhere ( the IAU perhaps) to be officially added to the list. And get given a proper name. $\endgroup$
    – Andy
    May 17, 2016 at 7:55

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As the comments already say, an object being a dwarf planet is a matter of convention. If the IAU says it's a dwarf planet, it's a dwarf planet. Otherwise, it's not. The requirements you are listing from Wikipedia are the IAU criteria for pronouncing objects as dwarf planets, but that does not mean that all objects fulfilling these criteria are dwarf planets. (don't ask me for the reasonings of the IAU, i'm not an expert on astronomer's brain twists)

There are a lot more examples of objects that could be dwarf planets, and are considered as being that by many researchers, despite these objects not having the status of dwarf planet. Wikipedia's List of possible dwarf planets has about 200 objects facing the same issue as 2007 OR10.

edit: as someone in the comments mentioned, not all objects on this list are actual candidates for dwarf planets (which is not what I meant, but I might indeed have implied this)

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  • $\begingroup$ Part of the issue with that list is that there are not enough observational data to decide where they belong $\endgroup$
    – SE - stop firing the good guys
    May 17, 2016 at 12:09
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The IAU recognized three dwarf planets as part of its declaration of a planet definition in 2006: Ceres, Pluto and Eris. In 2008, the IAU named Makemake and Haumea under dwarf planet naming rules because of their high albedo from which they expected the bodies would prove to be dwarf planets. Other than these, no other (likely) dwarf planets fall within the albedo which the IAU set for recognizing a dwarf planet (I think the albedo is 0.1 the IAU has set). So the IAU doesn't bother recognizing any more dwarf planets. Unlike Haumea and Makemake, Gonggong wasn't named as a dwarf planet.

So the reason is Gonggong's albedo which is 0.14 (and thus above the set 0.1 if I'm correct about that value).

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  • $\begingroup$ Can you link to a source that explains the albedo limit for dwarf planets? $\endgroup$
    – rubo77
    Dec 28, 2020 at 18:00
  • $\begingroup$ It sounds strange: you say Makemake has over 0.1 and Gonggong has 0.14, so what is the difference? $\endgroup$
    – rubo77
    Dec 28, 2020 at 18:02
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    $\begingroup$ @rubo77 If I had the source, I wouldn't speculate about the value. Magnitudes go upside down: Higher number means lower brightness (a darker body). "above" refers to the number in my answer, not to the brightness. $\endgroup$
    – Greenhorn
    Dec 28, 2020 at 19:01

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