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Old 11-19-2017, 08:15 PM   #1
myrmidon
 
Join Date: Feb 2015
Default Help with Space Setting [SF]

I am running a fairly conservative sci-fi campaign, with humans at TL 10. They just encountered an alien species, at TL 11, and are heading to visit their home planet. I am struggling with two things, one about the home planet and one about the aliens. I (mostly) randomly generated the aliens, and have the basic stats from the planet from when I generated the aliens (atmosphere and gravity). I like having dice determine story elements. It gives the game extra excitement and unpredictability, even for me as a GM.

1) First question: the planet. The aliens are an ammonia-based life form, so I have assumed that the planet has an ammonia atmosphere. Is that necessary for an ammonia-based lifeform? There are brief descriptions of ammonia-based planets on S82 and ammonia-based lifeforms on S138-139. But I am having trouble what the planet would actually look like, as in, how would it appear to our senses? What does it look like? It is generally mountainous, but what does the dirt and rock look like? Does the ammonia cause discoloration? What do the indigenous plant life look like? It's probably not green. I am mainly looking for help in visualizing it for myself so that I can describe it well to my players.

2) Second question: the aliens. The aliens were randomly generated as a tri-axial lifeform. I have been able to imagine, draw, and describe that to my players. I have been able to justify it so far in my mind because they live in a mountainous area and clamber about a lot, and it helps to have all kinds of extra manipulators to climb and hunt. But I have been struggling with if that would actually occur. Generally, life is fairly optimized for its environment. And, in gravity, two sides is much more efficient than three. How would three sides develop in gravity? They have already been introduced, so they can't be ret-conned now, but I thought it would be helpful to discuss.
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Old 11-19-2017, 08:35 PM   #2
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Default Re: Help with Space Setting [SF]

1) My understanding is that "ammonia-based" is generally talking about the biological solvent (i.e. your aliens are ammonia-based in the same way we're water-based) and not necessarily the atmosphere. That said, our atmosphere being oxygen-heavy is a consequence of our biological solvent being water - the purpose of photosynthesis is to convert carbon dioxide and water into sugar, with oxygen gas as a byproduct. Given how thermodynamically stable nitrogen gas is, it seems likely to be the byproduct of a biological process to produce an energy unit from available materials and sunlight.

2) I'm not sure I follow. What about gravity favours bilateral symmetry? Starfish have five legs; a triaxial alien doesn't seem that weird by comparison.
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Old 11-19-2017, 08:53 PM   #3
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2) I'm not sure I follow. What about gravity favours bilateral symmetry? Starfish have five legs; a triaxial alien doesn't seem that weird by comparison.
I hadn't thought of starfish. But I was thinking of animals that walk upright. As far as I can recall, all land-based animals are bilateral (and even most mobile marine life).

Thinking about it, the aliens in 'Arrival' were similar to a jellyfish, which is multilateral?
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Old 11-19-2017, 09:03 PM   #4
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Default Re: Help with Space Setting [SF]

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Originally Posted by myrmidon View Post
...
1) First question: the planet. ... What do the indigenous plant life look like? It's probably not green. I am mainly looking for help in visualizing it for myself so that I can describe it well to my players.
...
The plants are going to be whatever color captures the most usable light from the system's star (assuming they use photosynthesis). What sort of star is the planet orbiting?
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Old 11-19-2017, 09:03 PM   #5
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Given ammonia's boiling point I'd expect a cold planet with ammonia oceans and nitrogen. CO2 and methane atmosphere. The methane being the result of biology converting the NH3 and CO2 to CH4 and N2.
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Old 11-19-2017, 09:05 PM   #6
Ulzgoroth
 
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Default Re: Help with Space Setting [SF]

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Originally Posted by myrmidon View Post
1) First question: the planet. The aliens are an ammonia-based life form, so I have assumed that the planet has an ammonia atmosphere. Is that necessary for an ammonia-based lifeform? There are brief descriptions of ammonia-based planets on S82 and ammonia-based lifeforms on S138-139. But I am having trouble what the planet would actually look like, as in, how would it appear to our senses? What does it look like? It is generally mountainous, but what does the dirt and rock look like? Does the ammonia cause discoloration? What do the indigenous plant life look like? It's probably not green. I am mainly looking for help in visualizing it for myself so that I can describe it well to my players.
If the life is ammonia-based in the sense that we are water-based, their environment needs to be high pressure, cold, or both. Ammonia is a gas in human-tolerable conditions.

Ammonia might not be the main component of their atmosphere, or even a particularly large one if their general temperatures are comfortably below the boiling point. It should be noted that ammonia has a narrower liquid range than water - about 44 K instead of 100.

Ammonia is generally reducing in terms of electrochemistry, so you're going to need a reducing atmosphere - not too out there, Earth's modern oxidizing atmosphere is a result of photosynthesis dumping lots of waste oxygen into it. That does, however, suggest that major energy-nutrients will be oxidizers rather than things that can be oxidized. Not sure what to propose for that, especially for big polymers suitable for storage!

I'm not sure how a reducing atmosphere interacts with geology - I'd think it would be less able to corrode elemental metals, which is a bit of a significant factor.

Plant color probably doesn't follow in any straightforward way from this. It's going to be a function of the spectrum of sunlight that reaches the photosynthesizers, on the one hand, what sorts of energy-gathering pigments local life has had the luck to hit upon on another hand, and potentially what the key energetic thresholds for the photosynthetic biochemistry are on a third hand.
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2) Second question: the aliens. The aliens were randomly generated as a tri-axial lifeform. I have been able to imagine, draw, and describe that to my players. I have been able to justify it so far in my mind because they live in a mountainous area and clamber about a lot, and it helps to have all kinds of extra manipulators to climb and hunt. But I have been struggling with if that would actually occur. Generally, life is fairly optimized for its environment. And, in gravity, two sides is much more efficient than three. How would three sides develop in gravity? They have already been introduced, so they can't be ret-conned now, but I thought it would be helpful to discuss.
Earth has had trilaterally symmetric life, as well as higher symmetries. What's better about bilateral types?

(Also, evolution is less 'survival of the fittest' than 'survival of what survives' - natural life is rife with inefficiencies from features that just happened to be how the organisms that made it through did things. Maybe because they had no competitor that did it more sensibly, maybe because they beat that competitor out on unrelated points or even pure luck.)
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Old 11-19-2017, 09:08 PM   #7
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I hadn't thought of starfish. But I was thinking of animals that walk upright. As far as I can recall, all land-based animals are bilateral (and even most mobile marine life).

Thinking about it, the aliens in 'Arrival' were similar to a jellyfish, which is multilateral?
Most of the animals people immediately think of are vertebrates, which are a clade pretty far down the lines of development.

Arthropods are bilateral too, to be sure.

Both of those groups established themselves as bilateral before becoming terrestrial, though.
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Old 11-19-2017, 09:11 PM   #8
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(Also, evolution is less 'survival of the fittest' than 'survival of what survives' - natural life is rife with inefficiencies from features that just happened to be how the organisms that made it through did things. Maybe because they had no competitor that did it more sensibly, maybe because they beat that competitor out on unrelated points or even pure luck.)
This is very true, there are numerous 'design flaws' that are well known in humans* and other animals, that occurred via the process of evolution. Realistic hypothetical alien lifeforms should not be optimal in all facets.

* for example, breathing via an orifice used to ingest food and water is clearly unwise engineering, as evidenced by the number of people who choke to death from various food and drink based misadventure.
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Old 11-19-2017, 09:29 PM   #9
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Most of the animals people immediately think of are vertebrates, which are a clade pretty far down the lines of development.

Arthropods are bilateral too, to be sure.

Both of those groups established themselves as bilateral before becoming terrestrial, though.
Almost all the multicellular animal phyla are bilateral. Sponges are irregular; coelenterates and ctenophores are radial; echinoderms are secondarily pentagonal, which is approximately radial. That's pretty much it, unless you count oddities like trichoplax.

It's actually a logical design. If you eat other living things there's a fair chance you want to move around looking for things to eat. If you do that, it's efficient to have your distance sensors clumped near the front, and to have big nerve ganglia there. Nonbilateral symmetry seems to go with having a pretty minimal nervous system, and then I don't think you get sapience. Nor rapid movement, though lots of animal phyla are slow-moving.
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Old 11-19-2017, 09:49 PM   #10
Ulzgoroth
 
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It's actually a logical design. If you eat other living things there's a fair chance you want to move around looking for things to eat. If you do that, it's efficient to have your distance sensors clumped near the front, and to have big nerve ganglia there. Nonbilateral symmetry seems to go with having a pretty minimal nervous system, and then I don't think you get sapience. Nor rapid movement, though lots of animal phyla are slow-moving.
Front-back orientation and degrees of symmetry are very different questions. There's nothing stopping you from having higher-order symmetry and being elongated along the axis of symmetry with front-clustered sensory and processing organs.

Bilateral symmetry does have a distinctive benefit in supporting top vs. bottom differentiation (front vs. back for us weird uprights, but that's much later) and perhaps providing simplification for appendages that cooperate between symmetry units. The former, at least, seems like something rather useful for terrestrial life - but the bilateral clades were bilateral long before being terrestrial, so that's not why they did it.

EDIT: While molluscs are basically bilateral, I think, it's easy to imagine something on the squid or octopus sort of body plan that actually has 4 or 8 fold underlying symmetry. That's not so helpful of course when we specify land-dwelling.
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