The same is actually true of Europa, one of Jupiter’s moons, which very likely hosts an ocean of liquid water underneath its surface of ice. An interesting thing about it is that if there is life on Europa - which I hope there is, because the universe can get so lonely sometimes - it will have been heated not by the Sun, but by gravity. (The push-pull effects between Jupiter’s gravitational pull and that of its nearby but less massive fellow moons oscillates Europa’s barycenter, creating seismic waves. The friction heats the moon.)

This opens up the possibility that life may leapfrog from the outside of a star system toward the inside, following the inward migration of asteroids.

Even if they show up to proselytize?

It’s not part of the panspermia theory proper, but there is a subset of the idea called directed panspermia - there’s the random stuff happening, but there’s also some aliens out there deliberately seeding rocks and shooting them out into interstellar space.

Such an effort would be very resource-intensive, I would think. And - assuming that it’s not the equivalent of an intergalactic Safeway sending out seeds for later harvesting of biomass - one of the better rationales for such activities would be religious. As in, “God wants us to fill up the universe with life, so let’s get cracking on these bioasteroids.”

I’ve always gotten that end of the argument, which is I suppose why I’ve viewed the theory as far-fetched optomism. Nice, yes. But “I want aliens” is not necessarily a good argument for why something is likely.

Though, really. I do want aliens.

With that assumption in place, then life can start anywhere in the universe and spread through the transport mechanism. The initial “invention” of life remains very unlikely, but you have trillions of potential places for it, instead of just one. “It happened somewhere else and then drifted here” is much more likely than “it happened here”.

I don’t know about that. Unless we find life elsewhere its unnecessary. If it didn’t happen here then we would not be around to say “gee life is so rare its unlikely that it happened here.” Its kind of a derivative of the anthropic principle.

(I think I’ll update the post with it.)

It’s a numbers game. Simplifying assumption: the transport mechanism is viable, widespread, and easy/automatic - impacts on planetary surfaces that carry life-bearing rock out into deep space is pretty good as far as those go.

With that assumption in place, then life can start anywhere in the universe and spread through the transport mechanism. The initial “invention” of life remains very unlikely, but you have trillions of potential places for it, instead of just one. “It happened somewhere else and then drifted here” is much more likely than “it happened here”.

The analogy I like to use is rock music. Is there rock music in your town? Sure. Was it invented there? No, it was invented in (a hundred) other places, and CAME there. It’s a more likely scenario that you live in a place that has bands who were inspired from some outside source, than it is that you have bands who invented it themselves.

That’s what I’d understood. I just don’t know why panspermia as an origin theory is any more plausible than life starting on earth. It reminds me of those arguments about how God was created. “If it’s not clear how we generated, so there must be a God, then how was God generated?” I’d rather keep the impossibility close to home instead of flinging it a couple iterations of impossibility away. Call it occam’s razor of creation theory.

I love the water thing. Edgar Rice Burroughs for the win.

Also: the various current Mars missions have revealed that there was definitely running water on Mars’ surface in it’s history. There is also growing suspicion that there is liquid water below Mars’ surface right now. If so, there could be microscopic life (at least) in Mars right now.