[Space] A World design question regarding "Hadean" and "Ice" planets

[t@nya]

Originally Posted by Agemegos

Surely that has been obvious for ages?

Yes, but now the actual percentage (ratio) between gas giant and the total mass of its moons is known. The mass of every gas giant system in our solar system is that same 1:10,000 ratio and the science shows that the same ratio would apply to extrasolar gas giant systems.

[Ieldra]

Originally Posted by Malenfant

Well, if the MMWR is enough to hold onto a breathable atmosphere now when it's warm in the star's giant stage, then it must have been enough to hold onto any gas (including hydrogen) when it was cold when the star was main sequence.

Really? I need to check the formula when I get home. If you're right, I'll have to think of a fancy explanation. Too bad, I always liked the idea of inhabitable gas giant moons. My fictional TL11 civilization would have been able to make them so, but I would have preferred to get one without large-scale engineering.

After over 8 billion years? It's going to be tidelocked. Iapetus is in a distant orbit around around Saturn and it's 4.5 billion years old and it's tidelocked - and the bigger a moon is, the faster it gets tidelocked.

OK, it is probably tidelocked. Even so, that alone won't be much of a problem as it isn't tide-locked to the star, as long as tidal forces aren't strong enough to make the moon uninhabitable because of volcanism.

If the system is 8.35 Ga then the F9V is likely to be right at the end of its life, in its AGB stage. It'd be heading toward a mira-like giant stage, and getting really puffed up and pulsating irregularly. Over a span of about 10 million years it's going to increase in luminosity by at least 100 Sols and it'll start absorbing the innermost planets.

As I said, I only programmed the World Design Sequence. The program unfortunately doesn't save the original spectral class of a star transformed into a giant. Maybe I made a mistake when looking it up in the table. The World Design Sequence also doesn't simulate the different phases of the giant stage. Give or take a few hundred million years, make the original into a G0 or whatever, I'm sure there is some combination which will work for a hundred-million-year period of relative stability within the giant phase.