Directed Panspermia...wouldn't it be cool if...

[skep155]

The following is just pure speculation dreamt up on a boring Wednesday afternoon, but if life on Earth was 'seeded' by extraterrestrials either intentionally or by contamination billions of years ago, then all life in the Galaxy could be conveniently located within fifty light years of us, neat huh? Presuming of course that they only had sub-light speeds to work with and didn't have any fanciful sci-fi technology like warp speed or wormholes. It would be like a tiny village of life in one small pocket of the galaxy, dozens or even hundreds of life bearing worlds.

So there's no evidence for it...but it's fun to speculate sometimes.

[Jetlack]

Yes i think that's a popular fantasy many of us have :-) However i'm more inclined to think the non-directed panspermia is more credible.

[Bynaus]

The stellar neighorhood (of ~50 LY, as you suggest), was very different 3.5 billion years ago when life appeared on Earth. The stars that were that close to the Earth back then are now scattered over the entire milky way galaxy.

[Drunk Vegan]

Even at sublight speeds a radius of 50 lightyears is highly improbable for all life in the galaxy. Even at sublight speeds, only takes something like a million years to colonize the entire galaxy.

[agingjb]

Perhaps it is more likely that the Earth will be the origin of local panspermia, inadvertent or directed, in the future.

[Van Rijn]

Even at sublight speeds a radius of 50 lightyears is highly improbable for all life in the galaxy. Even at sublight speeds, only takes something like a million years to colonize the entire galaxy.

That depends entirely on the assumptions you make. For a million years you're talking about an average velocity of about 10% the speed of light, and billions of colonizations. Some might consider that extremely optimistic.

[eburacum45]

Let's assume there was a single instance of 'directed panspermia' five billions of years ago which only affected stars within 50ly of the originating star (I prefer to use the term 'translocation' for the deliberate transfer of life from one star to the next, but that is another matter).

There would be about 2000 stars within such a volume, with a wide range of velocities compared to each other. After 5 billion years those stars would have spread out all over the local arm of the Galaxy and beyond; they won't be near each other any more. So a single translocation event like that would leave a very diffuse trace in the current era.

[Hlafordlaes]

@OP,

If you're into Star Trek, the Original Series had an episode on the idea of panspermia, as did Next Generation.

[Noclevername]

Even at sublight speeds a radius of 50 lightyears is highly improbable for all life in the galaxy. Even at sublight speeds, only takes something like a million years to colonize the entire galaxy.

But you missed the point of the OP: the only life would be that within the 50 LY radius, and that would be "all the life in the galaxy", the rest would be barren (not having had the benefit of our "seeding") or at best have only scattered, single natural lifebearing worlds.

[Drunk Vegan]

But you missed the point of the OP: the only life would be that within the 50 LY radius, and that would be "all the life in the galaxy", the rest would be barren (not having had the benefit of our "seeding") or at best have only scattered, single natural lifebearing worlds.

I'm not really sure I did. He was assuming extraterrestrials moving at sublight speeds, intentionally or unintentionally bringing life to other worlds - what would make them stop at a sphere of 50 light-years? Once they'd covered that distance it's highly unlikely that any event would be able to bring their civilization to an end. It seems far more likely that if you've already colonized/visited planets within 50 light-years, you'd continue on to the rest of the stars.

And at those sublight speeds, with millions/billions of years to work with you've got time to colonize the entire galaxy many times over, or contaminate it, if you don't actually spread life on purpose.

[Drunk Vegan]

That depends entirely on the assumptions you make. For a million years you're talking about an average velocity of about 10% the speed of light, and billions of colonizations. Some might consider that extremely optimistic.

True, for 200 billion stars over one million years, you're talking about 1000 colonizations per year, to cover one billion stars. If we're talking about intentional colonization, then it doesn't seem unreasonable that maybe 1 in 200 would actually be worth colonizing (not baked by nearby radiation, has planets, planets can support life or have useful resources).

1,000 stars being colonized every year is a bit high, but once you're talking about tens of millions of colonized stars, 1,000 of them deciding to colonize one more star is a pretty insignificant number. It grows exponentially, the longest period is at the beginning of the expansion.

Of course the species in question has to be fairly parasitical and territorial to actually have the desire to do so - I have faith that humans would fit the bill nicely, but no idea if there are any alien psychologies that would suffice.

[Noclevername]

I'm not really sure I did. He was assuming extraterrestrials moving at sublight speeds, intentionally or unintentionally bringing life to other worlds - what would make them stop at a sphere of 50 light-years? Once they'd covered that distance it's highly unlikely that any event would be able to bring their civilization to an end. It seems far more likely that if you've already colonized/visited planets within 50 light-years, you'd continue on to the rest of the stars.

And at those sublight speeds, with millions/billions of years to work with you've got time to colonize the entire galaxy many times over, or contaminate it, if you don't actually spread life on purpose.

That's assuming they kept their motivations and capacity for doing so. They could have lost either, or simply moved on to other projects-- maybe they passed a tech singularity and now have no interest in mere organic life. They could have wiped themselves out with a genocidal war. They could have developed into a hive-mind and got collectively bored with the whole project. Or maybe they just fly very, very slowly-- relativistic flight, where a dust mote hits with the force of a nuke, is more dangerous that taking the walking-pace path, and maybe they're the cautious sorts. Slow and steady wins the race!

Too many unknown variables to say for sure. It could even be a combination of several factors.

[Somes J]

Given that, as has been mentioned, the stars that would have been within 50 light years of Earth billions of years ago would probably be scattered all over the galactic disk by now, a better way of achieving such a scenario might be to have aliens evolve on a planet relatively close to Earth relatively recently in cosmic time and terraform a number of worlds immediately around their own solar system, then die off or leave for some reason. However, that leaves you with the only other planet in the galaxy with naturally complex life just happening to be within 50 light years of Earth, which is a big coincidence, but it is in principle possible, just extremely unlikely.

Maybe a more plausible explanation might be a vanished pre-human civilization on Earth which colonized a limited area around our solar system before disappearing for some reason. Of course that has its own problems; without going into too much detail, there are serious issues with having a global technological civilization before ours that we don't know about, at least relatively recently in geologic time. Maybe they lived under the ocean - the ocean floor is poorly explored enough it becomes more plausible. Of course, the challenge then is figuring out how a technological civilization would develop in an environment where fire is impossible.

[AriAstronomer]

To Somes J
There are many problems with trying to advance technologically without being on land. Firstly and most fundamental, could you imagine trying to build anything with your flippers instead of hands? Bluenose Dolphins have a much higher EQ (encephalization quotient, the brain to body mass ratio, not an ultimate measure of intelligence but a rough guess) of monkeys, and yet monkeys have been cataloged to have started using tools and spears for hunting, which is a very elementary but fundamental step towards building a technological civilization. I think we are very blessed not only with intelligence, but with land.
Secondly, being in the water, looking up at the stars may be alot harder to do. I've personally never done it, but at depths below even 10m, can you see the stars at night underwater? Maybe the moon.....
I think you need the curiosity before you even attempt to search for what's out there, and if you cannot see the stars, you may live in blissful ignorance.

[Somes J]

Firstly and most fundamental, could you imagine trying to build anything with your flippers instead of hands? Bluenose Dolphins have a much higher EQ (encephalization quotient, the brain to body mass ratio, not an ultimate measure of intelligence but a rough guess) of monkeys, and yet monkeys have been cataloged to have started using tools and spears for hunting, which is a very elementary but fundamental step towards building a technological civilization.

A bottom-dweller could plausibly be freed from the need of swimming animals for streamlining and hence free to develop manipulatory organs. Cephalopods have decent manipulators (tentacles). I think an ocean-dweller could plausibly evolve an equivalent to hands.

Secondly, being in the water, looking up at the stars may be alot harder to do. I've personally never done it, but at depths below even 10m, can you see the stars at night underwater? Maybe the moon.....
I think you need the curiosity before you even attempt to search for what's out there, and if you cannot see the stars, you may live in blissful ignorance.

A bottom-dweller wouldn't know about the stars, but if they were curious about the world around them somebody might eventually try going to the top of the ocean, or try climbing one of the continental slopes, just to see what's there (the latter might be more plausible; I imagine initially they might imagine an infinite ocean of water over their heads, but a presumed big highland region gives a concrete goal for an explorer). And from there it's a relatively plausible series of developments to learning about the stars, assuming they could survive any significant period of time at or near the surface, or send robots and/or explorers with appropriate life support (terranauts?) up there.

The big problem with an advanced underwater civilization I think would be fire. I imagine it'd be much harder for them to get past the stone age than us; metal-working would be a lot more challenging in an environment where fire is impossible.