Stargate World Construction (Planetary Physics Help Needed)

[tarchon]

Yes, but why? And how can we counteract that?

A thick greenhouse atmosphere could trap in warmth, and volcanic activity caused by the parent planet's tidal forces on the moon's core could help create heat and the right atmosphere.

You can't really get around the problem that dark=cold. The heat has to come from somewhere. Tidal friction can warm the interior significantly, but I can't imagine what kind of system would have enough tidal friction to keep the atmosphere of a dark moon above the freezing point (with the surface solid), especially if tidal locking is complete. Best answer I can think of is that a very young moon would retain some of its accretion heat, but don't ask me how long that would last.
I think what I'd do is lock the rotation and put the moon's orbit dead on in the ecliptic plane so that it goes through lunar eclipse on at least some part of the near side on every revolution.
You could end up with a situation where 1/2 or more of the moon (the far side) enjoys a day-night cycle and one particular region in the center of the near side only gets short periods of indirect light. You would tend to get this with a moon in a relatively close orbit of a planet. For example, many of Jupiter's are eclipsed by the planet for long periods. It looks like Metis spends about 19% of its orbit eclipsed, so the center of the near side is only well illuminated for 31% of its orbit, during which the sunlight is rather indirect anyway.

 

[Snapdragyn]

I'm not sure why volcanic activity was ruled out so quickly. Keep in mind that moons of a gas giant can be substantially larger than Earth's moon. In fact, a quick google of Titan, Callisto, & Ganymede reveals that at least two of these large gas giant moons are thought to contain iron cores (& Ganymede is big enough that it could be considered a planet if it had a solar orbit).

Also, don't forget that many of the new extrasolar planets being discovered have gas giants with orbits much closer than those in our own system. This could be provide an additional heat source if you place your gas giant close enough for the moon to get Earth-like levels of solar radiation. The intense storms generated by mixing of the permanent dayside's furnace & the permanent nightside's freezer could contribute to the heavy rains needed for your rainforest biome (though getting the rain without intense storm winds could be an issue). You could build a lunar ecology with 'arctic' & 'tropical' biomes being centered on the mid-nightside & mid-dayside 'poles' rather than the axial poles, & temperate (& stormy) regions lying near the fixed terminator.

Hmm, I might have to yoink this.

 

[painandgreed]

Something like an earthlike planet around a larger than jupiter planet should be fine. It would be more of a duel planet system than a moon/planet system. The distance that the earthlike planet would have to orbit the gas giant would more than likely put it outside most of the harmfull radiation from the gas giant. The Em radiation could warm the earth-like planet however, it's been shown that even a planet that is tidally locked with one face always facing towards the sun can still maintain a liveable temperature on the darkside due to a greenhouse atmostphere. Make it a mostly water world like ours and you're going to get a side of clouds that will come to the darkside and condence and give you your rainforest.

Having one side always facing the sun is the werid problem. One side facign the sun and one side always facing the gas giant would be the easiest configuration but then you'd have this constant huge full moon in the world. Perhaps mostly obscured by clouds but if the planet is close enough to make the earth-like planet habitable, it's still going to be pretty bright. You could have the earth-like planet rolling over and under the gas giant so that the gas giant moon is always at the horizon. Tilt it a little and adjust the rotation and you could have seasons.

I don't see any long term problem with habitablity of the planet unless you make it small and it would otherwise lose atmosphere to space (like Mars).

 

[domino]

Volcanic activity was ruled out beause I was wrong in my information. My bad.

 

[GuardianLurker]

As for the lights in the sky, you have a few solutions. If you're going for an aurora borealis effect, you've pretty much locked yourself into a high radiation solution (like the one you've already described). Here's another possibility though - large bioluminescent flying critters. The best bet here would probably be photosynthetic "blimp" air jellyfish. Depending on your taste they could be individually polychromatic or monochromatic, full aerial predators that descend to within tentacle reach of the ground, or even sentient philosophers; none of the options are mutually exclusive.

 

[tarchon]

It looks like if you had a 1000 K brown dwarf (not much more than a red glow), with a diameter about 1/10 the sun's, you could sustain decent surface temperatures with a 400,000 km orbit, which would be roughly the same distance as Io from Jupiter. More than likely, Jupiter itself could have met these conditions for a brief period in its early history, which is why Io is largely depleted of volatiles now. It would be kind of a transient condition, but you could maybe get a million years or so of decent weather.
There's a calculator (http://zenith.as.arizona.edu/~burrows/evolution3.html)if you want to punch some numbers for temperature. Anything much over 1000K will tend to put out decent amounts of visible light, and even a 1000 K source at that irradiance level is going to be comparable to interior lighting, albeit very reddish.

 

[Kemrain]

Now we have some decent suggestions going. Thanks people, this is great.

I think I've sold myself on the high radiation solutin, as I have excuses for why humans are able t survive it. It would also give the aurora effect, which would be smothered in dense cloud cover most of the time. An earth-sized 'moon,' mostly oceanic, around a large brown dwarf, tidally locked so that the inhabited side faces the dwarf and only rarely got sunlight and was eclipsed for much of it's orbit. If the light levels ara still too high we can throw in some volcanic ash to disperse more ofthe illumination and give the flaura another source of neutrients, right? We'd have a raindorest because the side that got the most sunlight would be mostly water, causing huge ammounts of evaporation and condensation around the globe on the darker parts.

Being close to the dwarf could cause the required volcanic activity, ala Io and (so they say) Europa. From what I understand, Jupiter puts out enough high energy radiation to make the surfaces of most of it's moons deadly to earth-type life, which could be mitigated here by the strong magnetic field (which would be warped badly by the dwarf's own field, right?) and thick atmosphere, right? I doubt, though, that it would be brought down to human-safe levels, and that's acceptable as long as it's not enough radiation to cook someone.

Any more ideas? Snapdragyn, yoink away, by all means.

- Kemrain the Grateful for the Assistance.

 

[tarchon]

Non-artist's impression of driving down the highway on the nearside of the hypothetical satellite (around 65 degrees east of the planet's zenith).

During the middle of the first shorter "day":

Just after the first sunset: