Quote:
Originally Posted by Nereidalbel
Planets being habitable is not explained be panspermia; that's just being the right distance from the parent star. As for being able to eat plants on other worlds, that's just luck. Billions of years of evolution are more than enough to create large differences, as well as planets having differing chemical compositions.
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It's worth noting that most of the things on
this planet aren't edible. Of course, that's partly the result of a billion-year arms race between things that like to eat and things that'd rather not be eaten.
I think panspermia is a perfectly fine explanation for having compatible biochemistries on neighboring planets, in a "soft" sci-fi game. As a rigorous theory it has numerous problems, but so what? Rule of Cool it for maximum campaign enjoyment.
If you want to make it a little more rigorous, you can always opt for "Ancient Astronauts" notions - an ancient civilization developed space travel, seeded the system, then collapsed (for whatever reason... space plague? Gamma ray burst? whatever). Leaving the descendants of the organisms they brought with them on all the worlds they visited. Some places look just like the earth-analogue, some look quite different. You can posit intelligent life, closely related to humans (as the descendants of old colonists, sent back to the stone age and unable to bootstrap themselves up to UT without fossil fuels left by past epochs that didn't happen on non-earth-analogue planets), or not. It's your game!
A more serious answer to your questions: Unless they're evolved for it, you're not going to get terrestrial seeds clinging to meteorites. On the other hand, what's to stop the whole system from being seeded by some exterior source specifically evolved for interstellar distribution? Lots of fiction has space-based organisms, or organisms with a partly space-based life cycle. Something like this: a great interstellar tree approaches the main star of the system eons ago, but is shattered by a rogue planetoid. Pieces of its destroyed body, with all the attendant microorganisms, parasites, and symbiotes that usually ride with it, fall to ground on most of the planets in the system. The great tree is gone, but conditions on the proto-worlds are similar enough to the host for some fraction of attendant life to survive. Everything gets seeded at the same time, all the biochemistry is roughly similar, and when intelligent life evolves on of the planets it finds that its neighboring worlds are strangely (or not-so-strangely, probably, from their perspective) hospitable.
As for the sentience problem, it's only as much of an issue as you want to make it. As another poster mentioned, we've been on this planet for several billion years (for a loose definition of "we") and only one technological species has evolved in all that time. So hey, if you don't want there to be sentient species on the other planets, there aren't. If you do, then there are. it's your game, and either is just as reasonable as panspermia in the first place.