Help with Space Setting [SF]

[lwcamp]

Originally Posted by whswhs

If you're dealing with a dim red sun, the blackbody spectrum is going to give you an even smaller fraction of UV than earth gets.

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.

Luke

[lwcamp]

Originally Posted by ericthered

the Gurps:Space planet generator insists on ammonia planets orbiting small red stars.

As I understand it, ammonia is quite sensitive to photodecomposition by UV light.

Luke

[whswhs]

Originally Posted by Ulzgoroth

Yeah, I fundamentally disagree, especially for factors that evolved early - and bilateral symmetry is one of the most extreme macroscopic examples of that. As I posted earlier, stuff in evolution can be very accidental.

I consider it highly plausible that bilateral life dominates the Earth because of bilateria scoring a first mover advantage on the worm bodyform and running away with dominance in the entire motile animal niche from there. And I don't see anything stopping a higher-symmetry worm from getting there first on another planet.

I would find that more plausible if we didn't have the echinoderms, an entire phylum that is secondarily radial. They're fairly diverse, too, with around 7000 species. So it's possible for a bilateral animal to change back to a nonbilateral body plan; the bilateral plan isn't there just because most of the animal kingdom got stuck there. But echinoderms have exactly the limitations I would be inclined to predict on biomechanical grounds.

(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.)

It's also not evident to me that the existence of a large number of bilateral creatures would do anything to suppress trilateral, pentagonal, hexagonal, or other symmetries. I mean, it's one thing if you propose that the bilats go around eating all the nonbilats, but then wouldn't that be kind of a way of saying that bilateral symmetry is advantageous for an animal? I'm not sure I see some other process by which the bilats would get into all the niches and shut the others out, especially since the Earth has had several mass extinctions that left many niches empty.

I think, though, what I really come down to is that I'd like to see a proposed model for the body plan and environmental adaptations of an animal with three, five, or some other number of sides greater than two. This is science fiction; we can accept improbabilities if they have plausible justifications.

(Saying "greater than two" makes me imagine a phylum of animals with one one side, structured like Möbius strips or Klein bottles!)

[whswhs]

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.

Ooh. Does that mean that stellar lifting isn't going to be such a good strategy for prolonging human survival?

[Ulzgoroth]

Originally Posted by whswhs

I would find that more plausible if we didn't have the echinoderms, an entire phylum that is secondarily radial. They're fairly diverse, too, with around 7000 species. So it's possible for a bilateral animal to change back to a nonbilateral body plan; the bilateral plan isn't there just because most of the animal kingdom got stuck there. But echinoderms have exactly the limitations I would be inclined to predict on biomechanical grounds.

(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.)

But once you have a working bilateral body plan, why would you switch?

Evidently the echnoderms found an answer to that - but the theory seems to be that that answer was polyp-style anchored suspension feeding. Followed by evolving back into more motile niches.

Originally Posted by whswhs

It's also not evident to me that the existence of a large number of bilateral creatures would do anything to suppress trilateral, pentagonal, hexagonal, or other symmetries. I mean, it's one thing if you propose that the bilats go around eating all the nonbilats, but then wouldn't that be kind of a way of saying that bilateral symmetry is advantageous for an animal? I'm not sure I see some other process by which the bilats would get into all the niches and shut the others out, especially since the Earth has had several mass extinctions that left many niches empty.

If you look at the present, you surely won't propose any likelihood that, say, an extinction of sharks would create an opportunity for non-bilateria to move in, would you? A box jellyfish lineage heading that way has so much more evolutionary ground to cover than a bony fish or squid. Most other radial types are barely ahead of plants in the running of that race.

So the urbilateria take the 'worm' bodyplan ages before anything else has that grade of motility as a lucky break, and expands outward from there. meanwhile, any other contemporary lineage has to either leapfrog past that gateway motile form somehow or successfully invade a gateway niche that is now full of more-mature bilateral species.

Originally Posted by whswhs

I think, though, what I really come down to is that I'd like to see a proposed model for the body plan and environmental adaptations of an animal with three, five, or some other number of sides greater than two. This is science fiction; we can accept improbabilities if they have plausible justifications.

I'm not sure why there's any difficulty in imagining body plans of more-than-bilateral worms or fish. Especially when you've got pentaradial worm-like sea cucumbers!

I do agree that terrestrial or surface-dwelling descendants of such a lineage would probably show a degree of derived bilateralism as a result of differentiating 'top' and 'bottom' facings.


(The understanding that through the early Cambrian animal life was predominantly living on the sea floor, not in the water column, does suggest an advantage for bilateral forms over contemporary non-bilateral equivalents. If any such equivalents existed.)

[dcarson]

Originally Posted by whswhs

Ooh. Does that mean that stellar lifting isn't going to be such a good strategy for prolonging human survival?

Controlling when and where the star flares is the basis if stellar lifting. So I think it doesn't matter anymore then forest fires prove that fireplaces can't be safe to use.

[thrash]

Originally Posted by ericthered

Note that the color may not be in our visual range: we evolved to use the color range we do because of similar factors to the choice of plant color and probably somewhat because of plants having that color. So the plants may all be black: the Gurps:Space planet generator insists on ammonia planets orbiting small red stars.

A nitrogen-carbon dioxide atmosphere will have windows of transparency mostly in the infrared. That shouldn't be too much of an issue -- our atmosphere is strongly UV absorbing, of course -- but it may condition the visual range of any animal sensoria.

If the OP needs more data on the atmosphere, I suspect Titan's is a good real-world model. Note that the astrobiological speculations I've seen for Titan were about methane-carbon dioxide based cycles, with ammonia as a moderator. That would reduce some of the problems with the high stability of molecular nitrogen.

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.

Red dwarf stars also take a relatively long time to cool down to their main sequence operating temperature. This implies that there may not be a continuously habitable zone for life to develop, in the sense of a range of semi-major axis values where the surface temperature remains within the bounds for the liquid solvent (ammonia, in this case) for hundreds of millions or billions of years, unless the star is also very old (which has problems for metallicity...). We may need to look at a very dim K-type star.

[Humabout]

1) Based on the extreterrestrial environments we have directly observed, rocks and ground look virtually the same everywhere because they are all sillicates. Most differences come from atmospheric deposites and the effects of solar radiation.

[lwcamp]

Originally Posted by whswhs

Ooh. Does that mean that stellar lifting isn't going to be such a good strategy for prolonging human survival?

Maybe? Once you posit the tech for stellar lifting, can you also build an artificial magnetic shield to put in the L1 position to deflect the erosive solar storm winds? I hadn't thought too much about the implications, it will need some good musing over to figure these things out.

Luke

[lwcamp]

Originally Posted by Ulzgoroth

So the urbilateria take the 'worm' bodyplan ages before anything else has that grade of motility as a lucky break, and expands outward from there. meanwhile, any other contemporary lineage has to either leapfrog past that gateway motile form somehow or successfully invade a gateway niche that is now full of more-mature bilateral species.

I'm not sure why there's any difficulty in imagining body plans of more-than-bilateral worms or fish. Especially when you've got pentaradial worm-like sea cucumbers!

I do agree that terrestrial or surface-dwelling descendants of such a lineage would probably show a degree of derived bilateralism as a result of differentiating 'top' and 'bottom' facings.


(The understanding that through the early Cambrian animal life was predominantly living on the sea floor, not in the water column, does suggest an advantage for bilateral forms over contemporary non-bilateral equivalents. If any such equivalents existed.)

You could look to the cephalopods for inspiration. Sure, they're bilateral. But the octopuses keep their "front" in the "up" position, with a somewhat radial arrangement of arms that gives them impressive mobility and flexibility. Perhaps an early mobile blob-thing could have first evolved in that direction? Similarly, it is not too difficult to imagine a radial thing with a somewhat squid-like arrangement and way of life.

Luke