Colonizing Large Moons

[Arkansas Warrior]

There are a few examples in BT of the colonization of plant-sized moons of gas giants or brown dwarves (is 'moon' the right term for something that orbits a brown dwarf, or since those aren't technically planets, should the bodies orbiting them be called planets?).  Skyfog from Interstellar Players III is one, Barcelona is another, as discussed in Tamar Rising.  So what are the special issues to be confronted by colonists of such worlds?  A few come to mind.  Moons are generally (if not always) tidally locked to their planets, which can complicate the day/night cycle (especially if we're talking about a Brown Dwarf that puts off some light of its own).  Gas giants and the like often put out significant radiation , which is bad if it's the ionizing, cancer-causing kind (dealing with that is specifically mentioned as an issue with Skyfog), but if it's only infrared radiation, that might actually make a world warmer and more habitable, which could be useful.  Also, depending on how close to the planet it is, the moon might be subject to significant tidal flexing, leading to high amounts of volcanism (think Io), which might have some advantages but is doubtless mostly bad.  If you're lucky enough to settle a moon that has compatriots orbiting the same gas giant that can also be inhabited, you can really do well. Cray had a thread back in the day on that idea. I'm sure there's a lot that I'm forgetting (probably including more examples of the "large inhabited moon" phenomenon).  So.  Thoughts?  Comments?  Questions?  Bomb threats?


Edit: screwed up the formatting while trying to put the last link in.

[AlphaMirage]

Isaac Arthur's YouTube on the subject talks a lot about it. Tidal locking is problematic but it could be mitigated by space mirrors and shades. I figure most of the time the colonists on there live underground so you can make the day/night what you want it to be

[Wolf72]

I would (also) assume that most of those colonies were sub-surface.  Although I can't seem to get the terraforming projects from Master of Orion 2 out of my head.

[cray]

Campaign Operations' system generation rules give a few pointers on habitable moons. To address some points brought up here:

Radiation is a non-issue for a habitable moon with an Earth-like atmosphere for three reasons.

First, Earth's atmosphere is equivalent to about 10 meters of rock shielding and is good enough to block even high energy cosmic rays, never mind the (comparatively) moderate energy protons and electrons of gas giant radiation belts.

Second, granting the moon an Earth-like magnetic field would be enough to further block the radiation.

Third, you can always move the moon outside the radiation belts. While Jupiter's Io and Europa have severely radiation-blasted surfaces, outermost Callisto hardly gets any dose.

Tidal locking would be annoying, but you've got several options there, too.

First, being closer to the brown dwarf or gas giant would give a comparatively quick orbit. Ovan has a 96-hour day and Rigil Kentaurus has a 56-hour day. Hypothetical gas giant moon colonies could handle days in those ballparks, unlike the 17-day orbit of Callisto.

Second, tidal locking doesn't necessarily mean a 1:1 ratio. Mercury has a 3:2 tidal lock, going through 3 days per 2 orbits, and 5:2, 4:1, and 7:2 can be stable with enough eccentricity to the orbit. You can also mix things up by additional tidal influences, like big moons inward and outward of the habitable moon's orbit.

Third, there's the Project Aphrodite solution: spin up the moon's rotation.

[Prospernia]

I just chalk it up to the conditions of the environment; tidally-locked?  No big deal; too hot in the center, but too cold on the night-side, but kinda just right on the edge. And you can never really get lost on a tidally-locked world; no magnetic-field to protect against radiation?  A close, fast-rotating tidally-locked satellite, could have a dynamo due to tidal-stress and a, "Day", in hours not Earth-days as mentioned above. And even though Callisto doesn't get a lot of Jupiter's radiation, it's still blasted by solar-winds and cosmic-radiation.  Living underground is key!!!

Also, some game-effects could be, like, high-radiation means a random roll for criticals; if you get a crit, it shorts out.   Or the high heat or reduced heat, depending on the day/night side you're on etc. 

[Frabby]

Genuine question, is it true that brown dwarfs aren't technically considered planets? Because as far as I know this is a sliding scale of activity (even Jupiter iirc is already emitting more light than it should) up to the point where they light up as proper suns.

As for BattleTech, the Star League apparently was able to put sustainable human colonies on anything short of black holes.

A canon example of a tidally locked moon of a gas giant that springs to mind is Rosetta, and Keith always excels at making stellar and orbital mechanics a core aspect of his stories ("Starfire" is where Rosetta features). Though in this story the key player is the system's second sun.

Apocryphally, Andarmax was described as a gas giant with at least three dozen moons, many of which are inhabited and collectively form the "world" of Andarmax in BT.

[Natasha Kerensky]

So far in the real-world/universe, our solar system’s neatly ordered arrangement of small rocky planets towards the parent star and gas/ice giants away from the parent star seems to be the odd-duck.  Although this may be an artifact of the search techniques we’ve used so far, we’re finding lots of gas giants close to stars in exoplanet systems so far.

I don’t know if the BT planetary system generator is based on our solar system, the actual exoplanet population so far, or something else.  But if it’s based on our solar system, then the killer would be that most gas giant moons would be too far from their parent stars to get much solar flux.  For example, with a 1.5 bar atmosphere, Titan is probably the most habitable of our outer moons, but with surface temps under 100K, even methane exists as an ice on Titan — not very Earth-like.  Ideally you’d still want gas giants in the parent star’s habitable zone (between Venus and Mars for our Sun) to make gas giant moons competitive for settlement against other planets in the BT universe.  (Weird exceptions for story-telling purposes, notwithstanding.)

Based on space station research so far, the low gravities of the moons in our solar system is probably also a dead-end for mammalian gestation and development in the real world/universe — no one will probably ever have or raise families in these environments.  But that could be sidestepped in BT with a big enough moon and/or handwaving about germline alterations.

FWIW...

[cray]

Genuine question, is it true that brown dwarfs aren't technically considered planets? Because as far as I know this is a sliding scale of activity (even Jupiter iirc is already emitting more light than it should) up to the point where they light up as proper suns.

It's true: brown dwarfs are not planets. The difference between a planet and brown dwarf is fusion: brown dwarfs were able to sustain deuterium fusion for at least a fraction of their lives. Planets never had naturally-occurring fusion in their cores. (Mad scientists drilling to the core and detonating nuclear bombs does not mean a planet qualifies as a brown dwarf, but does mean it has scientifically deficient moviemakers.)

Jupiter does emit more energy than it receives from the sun, but that's from gravitational contraction, not fusion. Jupiter is often called a "failed star" but that's far from true. Jupiter is less than 10% of the mass required to sustain deuterium fusion, and about 1% of the mass required to sustain protium fusion. Brown dwarfs, on the other hand, either have ongoing deuterium fusion or exhausted that early on and are thereafter truly failed stars.

That difference happens at about 13 times Jupiter's mass, which is when core temperature and pressure is enough to fuse the sparse deuterium there. (It shuts down quickly as the brown dwarf cools with age.) At 75-85 times Jupiter's mass, the much more abundant protium could be fused and you've got a red dwarf.

I don’t know if the BT planetary system generator is based on our solar system, the actual exoplanet population so far, or something else.  But if it’s based on our solar system, then the killer would be that most gas giant moons would be too far from their parent stars to get much solar flux.

Campaign Operations' system generator can put gas giants in close orbits. Like observed exosystems, Campaign Operations notes the need for gas giants to form further from stars, which means they migrated inward and cleared out any rocky planets in the way.

Campaign Operations' rules also note that habitable moons of gas giants need to be in the life zone, though a sufficiently large gas giant might allow them to be a bit outside the outer edge of the life zone due to the gas giant's own heat.

[Maingunnery]

So when Jupiter is done with contracting, then it would become an Ice Giant?

[Natasha Kerensky]

No, gas giants are defined by hydrogen and helium almost totally dominating their mass.  And Kelvin-Helmholtz Contraction won’t change that elemental composition.  (That takes fusion and bazillions of years of life as a star.)

Ice giants are defined by elements heavier than hydrogen and helium (carbon, nitrogen, oxygen, etc.) being present in higher, if still minor, amounts.

[worktroll]

Not as I understand it. The "ice" refers to the constituents, not the temperature. Saturn & Jupiter are fair enough gas giants - mainly hydrogen & helium (Jupiter 89% & 10% respectively, Saturn 96% and 3%). Uranus is 83% hydrogen, 15% helium, 3% methane; Neptune is 80% hydrogen, 19% helium, 1.5% methane.) The non-H or He is small, but makes all the difference.

Cold Jupiter won't look a lot different from now, mebbe a bit smaller.