Talk:Planetary-mass moon

Luna
Why is the moon listed in the table as NOT being in hydrostatic equilibrium? (It's certainly not stated as such in the quoted reference.) — Preceding unsigned comment added by PaulxSA (talk • contribs) 07:16, 18 November 2019 (UTC)
 * Because it is not in hydrostatic equilibrium, and Pierre-Simon Laplace knew that already in 1799. Double sharp (talk) 14:50, 18 August 2021 (UTC)
 * Glad to see Luna so named here. I’ve added that alternative name to those of the satellites listed in this article because of the broad, indeed generic, use of the term “moon,” as in the present article itself. Luna’s a proper, unambiguous name that deserves especial currency in such contexts. Note its specific use in formal astronomy, as seen on Astronomy.com (e.g., https://www.astronomy.com/observing/exploring-luna-a-primer-on-what-you-should-know-about-our-moon/, https://www.astronomy.com/observing/luna-offers-up-a-valentines-day-gift/, https://www.astronomy.com/observing/sky-this-month-december-2023/; the last speaks of “our sister Luna.”).

If all stars were called “suns,” as they only occasionally are, the same problem would obtain, and indeed Sol is an alternative name of our home star. Mucketymuck (talk) 06:19, 3 December 2023 (UTC)

Strictness of IAU hydrostatic equilibrium requirement
The IAU requirement for hydrostatic equilibrium ("has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape") can't be read too strictly or else Mercury and Venus must not be planets since they are far from being in hydrostatic equilibrium. Instead the parenthetical "nearly round" part must be given weight. So the claim that the hydrostatic requirement is strict should be removed, and the right hand column of the table is inappropriate. Pulu (talk) 17:58, 10 February 2023 (UTC)

Vanth and Ilmarë
I am not sure about the (uncited) discussion of the TNO moons. It seems to be making the old argument (e.g. Brown's list of candidate dwarfs) that since Mimas is round, TNOs that small should be in HE. But now we suspect (Grundy) that the situation is different and that TNOs as large as Varda probably can retain enough porosity to not be DPs. Yes, Vanth and Ilmarë would get some tidal forces from their parents, which an iceball floating out on its own would not. But if Varda itself isn't in HE, can we seriously claim Ilmarë might be? The error bars don't even take it to Mimas' diameter. I guess the density matters, and we don't know it well. Double sharp (talk) 16:26, 4 July 2021 (UTC)
 * Removed Ilmarë but kept Vanth. Double sharp (talk) 04:39, 11 July 2021 (UTC)

In fact, the low albedos of Dysnomia (~0.04) and Vanth (~0.08) also raise suspicions that they are not solid either. Note that Dysnomia is not too far from Varda in size! Double sharp (talk) 12:28, 2 September 2021 (UTC)
 * Removed Dysnomia and Vanth, since they are in the size and albedo range Grundy et al. mentions. This is analogous to how we treat, which is in that size and albedo range, but has unknown density. Double sharp (talk) 12:41, 2 September 2021 (UTC)

This Article Violates NPOV
This article seems to be written as an oppostional diatribe to the IAU definition for what is a planetary mass object. The goal of the IAU definition was to help define "dwarf planets" as spherical in shape and exclude "asteroids" (other than Ceres), not get into an argument. In general, objects of 400km+ in diameter are candidates for gravity to be strong enough to 'round' it. The Moon is nearly spherical, hydrostatic equilibrium or not. Ryoung 122 17:04, 22 June 2023 (UTC)


 * I fail to see how it is a violation of NPoV to acknowledge that Luna, alongside many other objects, aren't in HE. ArkHyena (talk) 21:00, 10 March 2024 (UTC)