Wikipedia:Reference desk/Archives/Science/2021 July 21

= July 21 =

Density trends in giant-planet moons
The Galilean moons get less dense in sequence as one gets away from Jupiter. This is usually explained by primordial heat from young Jupiter creating a strong radial temperature gradient that vapourised the volatiles especially on Io and Europa, IIRC. (Tidal heating probably helped too, I guess.)

However, the large satellites of Saturn and Uranus don't show any such trend. Is the explanation for this known yet? Double sharp (talk) 03:04, 21 July 2021 (UTC)


 * Which primordial moons are you considering large?Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Hyperion, Iapetus, Miranda, Ariel, Umbriel, Titania and Oberon? Sagittarian Milky Way (talk) 05:13, 21 July 2021 (UTC)
 * The ones big enough that gravity should have collapsed them into solid bodies. So, the bodies you mentioned, minus Hyperion. Double sharp (talk) 05:28, 21 July 2021 (UTC)


 * There are so many variables, scientists can't even agree if Jupiter was once further than modern Neptune or closer than modern Mars. If you very spherical cowedly modeled it as an ideal gas of 1.3333 gram per mole particles that is not hotter in the middle, and the same joules per kg as the planetary gravitational binding energy and the orbits are same as today and the planets were twice as wide (which is the value given for Jupiter in its article) and they're as old as their parent planets' heat peaks then the planet effective surface temperature would be enormous (especially for Jupiter) and the number of square degrees of that in the sky would cause Europa and Mimas be roasted to incandescence even if they were of snow-like Bond albedo. But Mimas and especially Miranda would be less hot than Europa. And the heat wasn't dumped all at once of course and Jupiter had at least ~9 times more of it to get rid of than Saturn but not much more surface area to radiate it away. So I dunno, maybe Mimas wasn't roasted enough to cause the density trend. It's not implausible. Sagittarian Milky Way (talk) 19:46, 21 July 2021 (UTC)


 * Well, are there any known (stronger) trends for moons as they get farther from a planet? As this density is not a straightforward trend. Good topic! 67.165.185.178 (talk) 00:51, 22 July 2021 (UTC).