Need some help with my ALIENS game (Science questions, my players: KEEP OUT!)
As you may have noticed, I'm running a game in the PBP forum, set in the ALIENS universe... since the setting and the game system both seem to favour some degree of realism, I'd like to pick the collective brains of RPGnet for some advice on getting the science right in my science fiction horror.
I'm planning to set the game on a vaguely Earthlike moon orbiting a gas giant. I know that I want the surface to be covered in water, with ice sheets at the poles. I would also like to base a lot of the native life on those creepy deep sea shrimp that live in underwater volcanoes, so I suppose the sea floor will need to be pretty geologically active.
What would the day/night cycle and seasonal variation be like on a moon like that? I guess that there would be considerable variation in temperature as the orbit, relative to the local sun, would be quite erratic.
A good part of the adventure will take place in a sea-bed based research facility (supposedly studying the sea floor wildlife) beneath the polar ice, so a basic primer on how air pressure, water pressure and temperature make life difficult in such an environment would be helpful. I would probably like to have some scenes with water flooding into the base and native life-forms running amok, so any advice on how to set it up so that the experience is scary but not instantly lethal (in the 'station crumples like a tin can, everyone dies' kind of way) would be helpful.
Finally... does anyone have any good ideas for life forms that could live in that environment? I've got two already: the 'tubeworms' that form a structure rather like coral around volcanic vents and the 'parrotbugs': big trilobite/woodlice looking fuckers with massive powerful beaks they use to crack open the tubeworms' structure and suck them out.
Re: Need some help with my ALIENS game (Science questions, my players: KEEP OUT!)
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Originally posted by Perfect Organism What would the day/night cycle and seasonal variation be like on a moon like that? I guess that there would be considerable variation in temperature as the orbit, relative to the local sun, would be quite erratic.
It doesn't have to be. If you make the sun relatively hot (e.g. like our Sun, or even an F-star), then the gas giant will have to be so much farther from the Sun than the moon is from the gas giant that the moon is very approximately at a constant distance from the Sun.
If you want an erratic temperature, put the gas giant in an elliptical orbit.
If the moon is close enough to the gas giant, it might be "tidally locked". In this case, one side of the moon will always face the gas giant. If it's in the sky, it's always in the sky. The length of the day is exactly the same as the period of the orbit of the moon around the gas giant. For a fictional example of this, see the Quintaglio Ascension trilogy by Robert J. Sawyer ("Far Seer" et al.). In this case, any conteninents there are are likely to be either right underneath the gas giant, or on the side of the moon opposite the gas giant.
This isn't the sort of answer you want, but buy Blue Planet. Seriously. Buy the hell out of it. It has the answers to all of these questions and more. It's excellent and worth the money you'll spend when you buy it on clearance somewhere anyway.
Otherwise, the best I've got for you is: That's awesome, man. I love the ALIENS universe almost as much as I love gaming in it.
Tidal locking is very likely, agreed. So, if you go with tidal locking, think about what you've got.
Your day will actually be the length of your orbital period (well, this actually depends a bit on the relationship between the moon's period and the primary's period). If you're on the anti-primary side, you will never see the gas giant. If you're on the sub-primary side, you will never see the sun.
There will be two sources of radiant heating: direct solar, and indirect from the gas giant. In addition, tidal flexing of the mantle will probably produce a reasonable heat flux as well. Most of the temperature variation will probably come from the day/night cycle...night will probably be long enough, and affects the whole body simultaneously, so it might lose a significant amount of heat. The flux from the ground should be fairly constant, though, which may be enough to make life possible.
I didn't know that the moon could be tidally locked... I was initially thinking that it would rotate, causing massive tides in the ocean as the water was dragged towards the gas giant. This would mean that amphibious life would be relatively viable, at least in the equatorial regions. Is it possible for the primary to exert that kind of pull (i.e: many times the influence of the Moon on the Earth without causing the moon to be tidally locked?
I kind of like the idea of a huge ice cap on the side facing the primary though... would it seem plausible that there would be a volcanicaly active region underneath such a pole (I guess 'yes', since the mantle is being constantly pulled upwards by the gravity of the primary)?
What would gravity be like on a tidally locked moon? Would you actually weigh less on the side facing the primary?
Originally posted by Perfect Organism What would gravity be like on a tidally locked moon? Would you actually weigh less on the side facing the primary?
The primary won't be covering the entire sky. Nor will it outshine the sun.
Oh yeah, and who's saying the moon's orbital plane around its primary has to coincide with (or even lie anywhere near) that of the primary around the sun?
Originally posted by Leif Oh yeah, and who's saying the moon's orbital plane around its primary has to coincide with (or even lie anywhere near) that of the primary around the sun?
Well, in every stellar system where we've seen moons around gas giants (statistical sample size: 1), the plain of most moon orbits is pretty close to the plain of all the planet orbits.
Beyond the observation of our one solar system, there's also conservation of angular momentum arguments.
But, yeah, you can easily come up with reasons the moon's orbit is oriented any way you want it to be. (Something got Venus rotating backwards, and something knocked Neptune on its side, after all.)
Originally posted by Perfect Organism Is it possible for the primary to exert that kind of pull (i.e: many times the influence of the Moon on the Earth without causing the moon to be tidally locked?
*My understanding is that it takes better than a billion years for a primary body to eat up enough angular momentum to cause its satellite to become tidelocked -- and I think the satellite has to be pretty close for it to get tidelocked (our moon and Mercury being the examples that leap to mind). So if it's a newish system, or a captured planet or something . . . .
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What would gravity be like on a tidally locked moon? Would you actually weigh less on the side facing the primary?
Probably not detectably. I mean, the moon's yanking at you right now with enough force to drag the entire frigging sea a meter into the air -- do you feel lighter?
On the subject of your critters, I googled about for deep-sea life and methane hydrate, and came up with the PSU webpage here: http://www.bio.psu.edu/people/facult...er/cold_seeps/ . Some truly crazy things in that vein, including a giant isopod that made me think immediately of your parrotbugs. I'll edit with more as I find it.
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