Help with Space Setting [SF]

[Fred Brackin]

Originally Posted by thrash

A nitrogen-carbon dioxide atmosphere will have windows of transparency mostly in the infrared. .

Ah, I was wondering about that. What color of light gets through the atmosphere the best is even more important than what colors of light the star puts out the most.

This in turn leads us to _which_ infra red. Even just the 750 to 1500 nm of our near IR is somewhat problematic in terms of powering chemical reactions. If the IR in question is even less energetic than that the problem gets bigger as the energy content gets smaller.

[acrosome]

Originally Posted by whswhs

I tend to think that biomechanics on other planets will be generally similar to biomechanics on Earth. If we don't know of at least one example, it makes me think that maybe a structure has problems, even if we don't know what those are. Of course that's not conclusive, but I would be more receptive to a proposed morphology or organ if I knew of something like it here. Failing that, I'd like to see a somewhat detailed explanation of the structure, mechanics, and selective advantages for what's being proposed.

I'm not sure that's a great decision model. Not a bad one- it's always good to use the data that you have- but not great either, for such speculation, since you're talking about an N of 1.

Certainly we have critters on Earth that can give us clues for an elongated non-bilaterally symmetric body plan with sense organs concentrated on one extreme. Imagining a tenfold-symmetrical squid isn't hard, for instance. Take a squid, and give it ten or five eyes spaced around it's head instead of just two. (Even greater-than-twofold symmetrical organisms on Earth often have only one digestive orifice.)

Originally Posted by whswhs

Incidentally, I just looked up sea cucumbers and found that while they have internally pentagonal symmetry, they have gone from there to being tertiarily bilateral, with preferred dorsal and ventral surfaces and a front-to-back axis.)

This is a good argument that having greater-than-twofold symmetry does not preclude a twofold-oriented body plan. Because gravity. Other echinoderms are also good examples. So clearly I agree with you here.

[cptbutton]

Originally Posted by lwcamp

Red dwarf stars are often flare stars. Which means that sporadically you would be getting a lot of UV all at once. Whether plants could use this effectively is another issue (as opposed to simply having all of their cells sterilized). However, since it is currently thought that flare stars tend to massively erode the atmospheres of their planets this might not be much of an issue, since any red dwarf stars that are flare stars won't have life on their planets anyway. Of course, we're only now figuring this out so there might end up being unexpected ways for flare star planets to keep their air.

Asumming you get a way to keep the air, my thought is you get life that hibernates or lies as seed between flares. Then you get explosions of life during the flare, like flowers after rain in a desert.

Maybe the need to find a way to stay active longer was the driver towards intelligence.

[Ulzgoroth]

So on the non-bilateral organism subject, my take would be that it's entirely plausible but in the very likely event that their land-dwelling lineage went through a horizontal phase they will probably have significant bilateral development around the underlying framework - ventral features adapted to support and movement (and possibly manipulation at the front) and dorsal morphology atrophied or adapted to defense or manipulation.

To retain an unmodified rotational symmetry, or polygonal reflective symmetry would seem to only make sense if they somehow kept their axis parallel to gravity throughout their land-dwelling history, which does seem rife with problems for animals.

[myrmidon]

Thank you all for the feedback. You all never disappoint! I was reading various posts on the biological discussion to my wife just to show her how awesome you all are.

1) In terms of the planet, it is cold, as recommended in Space. What would the lifeforms breathe? Would plants photosynthesize something into nitrogen, and animals inhale nitrogen and exhale something? As for light, I want it to have light in the visible spectrum for the PCs. The sun could emit light with a peak at the lower end of the visible spectrum (and minimal or no UV light, since it decomposes ammonia according to lwcamp). Then the plants could be a dark greenish-blue or red (GMs preference, although red would match up with Earth plants reflecting in the middle of the spectrum). Rocks would look the same, as Humabout said. And ammonia is a dark blue with solvents in it, so the oceans would be that color.

2) Thank you for all the discussion on symmetry. whswhs expressed what I was thinking. I've drawn some pictures of the aliens. They have one set of legs and two sets of arms. They do have sensory organs located in the head as we do. They run on two each of the lower arms and legs, leaving the upper arms free. They sit on all three legs, like a stool. Could they run on two legs? I suppose the third leg could act as a tail. The trilateral symmetry allows them to roll and change direction easily, while climbing or running. I do like the idea of being trilateral, with some partial bilateral symmetry for efficiency (as several people noted with sea cucumbers).

[Ulzgoroth]

Originally Posted by myrmidon

1) In terms of the planet, it is cold, as recommended in Space. What would the lifeforms breathe? Would plants photosynthesize something into nitrogen, and animals inhale nitrogen and exhale something?

Definitely not. Diatomic nitrogen isn't analogous to diatomic oxygen at all. It's a very low-energy, non-reactive molecule. It's a likely exhaled metabolic byproduct, but it's not capable of being the basis of respiration. More like CO2 than O2.

EDIT: Your reactive gas that can coexist long term with ammonia is going to need to be a reducer. Maybe a sulfur molecule like H2S or SO2. Or Hydrazine perhaps?

EDIT2: Maybe it could be the ammonia itself, but I think that's relatively weak.

[lwcamp]

Originally Posted by myrmidon

As for light, I want it to have light in the visible spectrum for the PCs. The sun could emit light with a peak at the lower end of the visible spectrum (and minimal or no UV light, since it decomposes ammonia according to lwcamp).

Even the coolest red dwarf stars are about as hot as the filament in an old-style incandescent bulb. The hottest red dwarf stars get as hot as the filaments in halogen bulbs. So the spectrum of light you get would be similar to indoor incandescent lighting. Notably yellowish in color to human eyes, perhaps verging on orange-ish for the very coolest stars, even though they are called "red dwarfs". This light's spectrum is strongly peaked toward the red and infrared, so despite what our eyes see, the red and near infrared parts of the spectrum would give the highest spectral intensity for native autotrophes to use.

If the planet is far enough away for ammonia to condense out, that means it is not receiving as much sunlight as Earth. Combine this with the fact that the bulk of the sun's light is coming out at infrared wavelengths and the surface will be dimmer than that of Earth. Again, think of indoor incandescent lighting (although I haven't done the calculations yet to get the actual illuminance).

Luke

Luke

[AlexanderHowl]

The world is probably receiving 1% to 5% of the sunlight of Earth to get the temperatures required for ammonia-based life. They would probably breathe methane.

[thrash]

Originally Posted by myrmidon

What would the lifeforms breathe?

Autotrophs probably reduce CO or CO2 to produce methane (CH4), like methanogen bacteria on Earth. Heterotrophs (like your aliens) are methane breathers.

[myrmidon]

Thank you all for the guidance.

Autotrophs would reduce CO to produce methane, as CO2 is solid at the temperatures the planet will be to maintain liquid ammonia. Then Heterotrophs would breathe in methane and exhale CO? H2S is a liquid, though close to its boiling point, in the temperature ranges for liquid ammonia, and SO2 and hydrazine are solids, or close to that temperature. That means an atmosphere of nitrogen as the inert gas, some methane, and trace amounts of CO.

As for light, I'll go with it being in the yellowish-orange range to human eyes.

The whole color scheme of orange light, deep blue water, and dark greenish-blue or red plants would look very eerie, or dare I say alien, to a human.