Pondering Panspermia

Over the last few days I’ve neglected my duties to obsessively browse the last seven years of three journals:  Astrobiology, International Journal of Astrobiology, and Origins of Life.  In the process I’ve become converted to a more expansive version panspermia – life here probably originated outside our solar system. I’ve also learned: panspermia is no longer a marginalized view.  It may not yet be the majority opinion, but it shows up often in journal articles and conference proceedings, if not in summaries intended for wider audiences.

My interest in panspermia over the years was probably heightened by my sense that it seemed more believable than its apparent outcast status suggested – I may have hoped for the glory of being an early supporter of a crazy-seeming view that eventually became the consensus view.  But that hope neglected the prospect that many other young researchers shared my opinion – I’d have to distinguish myself among all those folks to gain much glory.

Academia is often run by an old guard ensuring that its public face reflects their old views, while younger folk quietly bite their tongues waiting for their chance to shine.  But just because you can see well enough to understand what those new generations will later say doesn’t mean you have much of an advantage competing with them – many of them, perhaps most, can see as well as you.

Long term prediction markets on academic questions could cut through this old guard deception.  But someone would have to be offended enough by this deception to fund such markets, and I see little evidence of this.  Most academic patrons just want to affiliate with the high status old guard, no matter what its views, and those who do care about particular views aren’t confident enough in them to risk supporting prediction markets that might not agree.

Versions of panspermia can be distinguished by how far/long life had to travel:

  • Orbit and Back – Early bombardments of Earth may have kicked some life up into orbit, to fall back down and re-seed Earth after big bombardments killed life on Earth.
  • Outer Solar System – Since the outer system cooled first, life had more time to evolve there, before some bombardment kicked life off it to Earth.  Mars and Ceres are two possibilities.
  • Comet Cloud – There is far far more water and clay a thousand AU out, it was all pretty warm long ago, and can long stay warm inside big comets.
  • Sun’s Nursery – There was even more water and clay around the thousands of stars that mixed closely for 100My in the 1-3 parsec nebula where our Sun was born.
  • Star Passing Cloud – In the galaxy’s main ring, every 50My each star comes within a few parsecs of a giant molecular cloud for a 3My period, and comet impacts kick life off planets in dust that takes ~100Ky to reach the giant cloud.  Within 10-100My such clouds become star nurseries.
  • Star to Star – Life that could survive for many millions of years could directly reach planets around distant stars.

This last version doesn’t look good, but the other ones seem feasible and likely.

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  • http://t-a-w.blogspot.com/ Tomasz Wegrzanowski

    Are there any major arguments for panspermia based on biochemistry of life? Any good (ungated) papers?

    • http://hanson.gmu.edu Robin Hanson

      I expect there are, though I haven’t reviewed the lit carefully enough to be able to cite some. The main argument I think is just that life seems so very complex and hard to evolve, so the larger a volume of space-time in which it could have evolved the better on that count.

      • Will Hewson

        It seems to me that it would be worth crunching some numbers on these scenarios.

        On one hand, compute how much space and time is available on Earth between the moment it was first cool enough to support some kind of life and the earliest moment we know there was life. A simple analysis would just do it in units of surface area * time.

        On the other hand, compute how much space and time was available on these other bodies, and multiply it by some kind of factor representing the probability that a life-containing chunk of that rock is going to get knocked off and hit the Earth. You might also need some kind of habitable zone overlap factor, since panspermia will probably only work at times when both the origin rock and the Earth are habitable at the same time.

        Of course this kind of analysis would have huge error bars, but it would probably be enough to mark some scenarios as extremely unlikely. Ceres, for instance, is such a tiny rock compared to Earth that the extra time can’t cancel out the space disadvantage. Likewise the Oort cloud has a lot of water (I’m not sure whether it was ever warm enough) but the probability of life originating on any particular Oort cloud object is low, and only a tiny number of Oort cloud objects have ever hit the Earth, and the collision rate between Oort cloud objects is small enough that life wouldn’t spread quickly between them, so that would probably turn out to be very unlikely too.

        Mars seems like the only scenario which would survive this first-order analysis looking anywhere near as likely as Earth origin — its 3x smaller surface area might be cancelled out by the fact that it became habitable a little earlier. We’d need, then, to start thinking about the probability that life would actually survive the interplanetary trip.

        Anyway, there’s definitely an opportunity for making progress with some simple number crunching here.

      • http://timtyler.org/ Tim Tyler

        That the simplest living things are rather simple has been hypothesised by many – including Cairns-Smith and S. Kauffman. The idea is compatible with the early emergence of life on Earth. So, the idea that early life is necessarily complex is a long way from being established – and so represents correspondingly weak evidence.

  • http://www.aleph.se/andart/ Anders Sandberg

    Ob SF reference: Greg Egan’s “Incandescence”. “Are you a child of DNA?”

    If one buys panspermia, then the galaxy is likely filled with life. Not only would many stars come into contact with the clouds, but occasionally life would spread from planets into new clouds. This would be worrisome from a Great Filter perspective.

    There would be a kind of competition as life spreads in the galaxy between kinds of life. A form that has a higher likelihood of infecting planets, getting into space again in new regions, and survive for a long time would presumably catch more planets than the less fit kind. Given that there have been several billion years of possible panspermia, that gives room for several generations.

    • http://hanson.gmu.edu Robin Hanson

      Yes, later steps in the great filter would have to be bigger, including perhaps steps we have yet to get through.

    • http://www.transhumangoodness.blogspot.com Roko

      “This would be worrisome from a Great Filter perspective.”

      Indeed… Very much so.

  • AP

    “If one buys panspermia, then the galaxy is likely filled with life.”

    Indeed. If you allow life far more time to evolve then the Fermi Paradox becomes even more paradoxical than before, though this in itself doesn’t make panspermia less likely.

    I would however be very hesitant to start believing a hypothesis for which “The main argument I think is just that life seems so very complex and hard to evolve”; (I mean, isn’t that the Creationist argument against the whole idea of evolution?!). That said, I think you’re right to say we should give the hypothesis more attention than we may have done before.

    I guess we just don’t know enough about the origin of life to make an informed judgment. Sure, allowing more time would presumably make the emergence of life less likely, but my understanding is that we just don’t know how long it would take for life to emerge from an environment with the right conditions. Perhaps the few billion years available on earth was enough; I would be hesitant to say that it wasn’t simply because there are other environments where more time was available.

    • http://hanson.gmu.edu Robin Hanson

      Life appeared on Earth within a few 100My or so after it was possible, and we don’t know it didn’t appear earlier.

      • AP

        Yes, but we don’t know whether said life emerged here or came from some outside source. If, as you suggest, life on earth originated elsewhere, then that strongly implies that a few 100My is not long enough for it to emerge (else we wouldn’t need the panspermia hypothesis).

  • Thomas M. Hermann

    What I find intriguing about panspermia theories is how can we test or verify them. Is it even conceivable that we can obtain the necessary information from the fossil record? Will we survive long enough as an organized civilization to collect the current evidence?

    On a smaller scale, let’s presume Venus once had substantial water and life, would there be any evidence left? If there is, would it be possible to connect it with life on Earth?

    For that matter, if we go extinct in the near future, how long before all evidence of our civilization is gone or unrecognizable? If there have been sentient species on this planet prior to us, is there any evidence that is long-lasting enough to testify to their presence? If we can’t establish that there has been sentient life on this planet prior to humans, how can we establish that it exists or existed elsewhere?

    • http://hanson.gmu.edu Robin Hanson

      Some claim to have found fossils of life on meteors that are older than Earth. If such claims were verified, they’d be clear proof.

    • tim

      Only recently have we been capable of leaving behind artifacts that would last more than mere thousands of years – things like nuclear waste or corrosion-resistant materials (like titanium). We’ve also performed major geophysical engineering; Mt Rushmore won’t last forever, but that’d piddly compared to stripping the planet of resources like fossil fuels that a future prospector would expect to find. So if there was sentient life on the planet prior to humans, they certainly didn’t nuke themselves into extinction.

  • http://theastronomist.blogspot.com/ The Astronomist

    I don’t understand how this theory could ever be proven with certainty or what it is supposed to imply for earth. The fossil record shows there was evolution on earth. So at best all you may have is the chance that primordial life travels around the galaxy on inhospitable objects. This doesn’t mean anything revolutionary to me or it seems many other astronomers who already believe that life does exist all around us (thought see the Fermi paradox , but that it is too distant/basic to communicate with. The places purporting panspermia, like the Journal of Cosmology , seem just as guilty of imposing only their views as the old guard is of theirs. I insist upon asking, how will you prove it?

  • jonathan

    I know very little about this topic but how does the formation of the moon figure into this? If the moon was formed by collision with another large object, then that could have added some of the necessary bits – without positing a need for vastly long travel on objects that we have no sign of here. Assuming collision is correct, then that would also have dramatically improved the possibility of development.

    With regard to probability, I may have mentioned this before, but “life” can exist in more places than higher order “life” and the moon is one aspect of that. Without the moon, we’d tilt a lot and that would make higher order, complex life really improbable if not impossible. If the moon were too close, too far, too big, too little, you have versions of the same problem. So the number of potential stars, potential planets then would possibly at a minimum require some stabilizing force on rotation and axis.

  • http://www.rationalmechanism.com richard silliker

    Why not? As good as any, better than most.

  • ravi hegde

    OK, so you manage to pinpoint the exact point for origin of life. So what?
    Isn’t it far better for us to invest intellectual energy into making something tangible or useful? The point is that most academic curiosities aren’t really useful to society, but merely serve as arbitrary in-group mores.

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