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Microbial test: Can this planet support humans?

December 22, 2011

Suppose we find a planet that looks habitable, based on physical factors of temperature, solar spectrum, water, elemental composition and so forth. But how can we really tell? What if we missed something, before we step down and try to live there? SFreader suggests we can try out some terrestrial microbes, and see if they survive and colonize the new world.

Which microbes would you test? And which organisms after that?

My first microbial suggestion: Desulforudis audaxviator grows deep underground, probably off hydrogen gas (H2) generated by radiolysis–chemical reactions from ionization caused by radioactive decay. The bacterium was discovered in a South African gold mine; it is believed to have been isolated underground for millions of years, although that is hard to prove. It needs no organic food, but adds reducing electrons to sulfate, and fixes carbon from carbonates.  Because it grows underground, it is protected from cosmic rays; such a bug is a good bet to grow on Mars.

11 Comments
  1. December 22, 2011 11:59 pm

    Just because a terrestrial extremophile can live there does not mean it could support humans! If the average temperature of the new planet was 200F we can find earthly bacteria (just head over to Yellowstone) who think that is a perfect environment. Microbes at the bottom of the ocean don’t mind a pressure of a thousand atmospheres, but we would. Your own example of desulforudis audaxviator being a good bet for Mars is in no way a canary for our ability to survive that particular coal mine.

    I’d say we’d be better to start with expendable animals that share our environment — cockroaches followed by rats.

  2. December 23, 2011 9:40 am

    Survive is a tough spectrum. Walk around in the air is one thing (and free oxygen implies something funky is going on — I don’t know of any abiogenesis methods of getting O2). Growing food in the ground is another. Yeah, with sufficient tools for extracting important chemicals you could probably do hydroponics, but your lab rats and cockroaches can’t — what would they eat?

    I like Charlie Stross’ concept of dropping “decorticated hominids” (people-like creatures that can’t think) as a test for whether a planet is survivable… his conclusion was that a very large fraction of this planet isn’t habitable by those standards.

  3. December 23, 2011 10:22 am

    John says that Desulforudis lives under more extreme conditions than we do.
    But Joel says that even cockroaches can’t live everywhere that we do, if “we” includes humans with advanced technology.

    I suggested Desulforudis as a start, just for a “ballpark” — If that can live, chances are other parts of the planet have parameters just slightly off, where humans could do better. Next, I would try Deinococcus (radiation-resistant) for life on the surface.
    After that, cyanobacteria (phototrophs), and lichens. We could farm lichens; reindeer live off them.

  4. December 23, 2011 10:25 am

    “Decorticated hominids” raises other issues.
    If they lack a cortex, how can they function?
    If they don’t have to function, just metabolize, why not tissue cultures in a culture machine?

    The point is not whether the whole planet is habitable. If someplace is habitable by something, I argue you can triangulate until you find a place for humans.

  5. Alex Tolley permalink
    December 23, 2011 12:59 pm

    We need to define habitable, and that means different things to different people. Clearly humans require the rest of the local environment to survive, and various levels of technology allow an increase in the habitable zones. Would a lifeless planet in the habitable zone of a star be considered habitable? Some will argue that it is not, because there would be no free oxygen, no terrestrial type life to feed upon, etc. Others will argue that this is irrelevant, technology will provide the means – living under “domes” with implanted terrestrial life, a land based space colony if you will.

    Such arguments often devolve into – “but what about…[X]” where X is some perceived danger – radiation, meteor impacts, solar flares, virulent local biology,…. More sophisticated arguments are about the difficulty of establishing terrestrial type ecologies (terraforming).

    I suspect the position people take on this issue is more dependent on education and outlook (even politics) than on reality. Historically, humans have expanded as far as technology and access to resources can take them. If we didn’t know the Inuit existed, would many people even believe people could survive with “simple” technology in the arctic regions?

    The other issue for me is the astrobiology/planetology definition of habitable zone. They all center on the idea of a planet being within the zone of a star where free water can exist on the surface. This is not just earth centric, but also rather early C20th, with visions of rich ecologies fed by solar energy. Yet as we discover microbes in the deep lithosphere, and free water beneath the icy surfaces of moons in the outer solar system, the concept of life bearing starts to get much hazier. And recently John Gribbin has published a book (Alone in the Universe) suggesting life (at intelligent life) may even be unique to earth, in all the universe, rendering the idea of “habitable zone” planets almost an abstract concept.

  6. December 23, 2011 3:14 pm

    Alex, you’re right about the Inuits; how could we imagine that they get along. For that matter, I can’t imagine how preindustrial people survived the New England winter. The same is true of animals; how do small birds and mammals get through it?

    The question of oxygen doesn’t bother me because microbes existed at least a billion years before there was oxygen. All we have to do is seed a planet with cyanobacteria, and there will be oxygen and organic soup soon enough. Stan Robinson had the right idea there. (This assumes we feel it’s ethical to seed a sterile planet. But I think the planet’s unlikely to be sterile to begin with.)

    I disagree with the idea that we’re alone in the universe. All the meteorites have left-handed amino acids. On Earth, life appeared when the soup had barely cooled–and probably got destroyed and evolved again, many times. I think the universe is full of life, and so is the “multiverse” of all possible universes out there.

    • Alex Tolley permalink
      December 24, 2011 3:44 pm

      All we have to do is seed a planet with cyanobacteria, and there will be oxygen and organic soup soon enough.

      “Soon enough” being how long exactly? 😉

      I disagree with the idea that we’re alone in the universe. All the meteorites have left-handed amino acids. On Earth, life appeared when the soup had barely cooled–and probably got destroyed and evolved again, many times. I think the universe is full of life

      I think it is likely too. However, I also think this is more of a belief with potentially very shaky foundations. We really need some evidence to support it.

  7. SFreader permalink
    December 23, 2011 5:37 pm

    I was hoping to find out what range of microorganisms would be needed to test livability across the spectrum of life as we know it on Earth but definitely centered on human beings.

    Such a test would, I think, provide better information than a straight chemical/machine analysis since machines can only test whatever they’ve been programmed to test. Organisms on the other hand thrive, sicken/weaken or die and while doing so provide a blow-by-blow account of what exactly is happening to them by the reactions that continue, become modified or stop. (This could result in a new field, micro-pathology/forensic.)

    If one could select organisms that are ‘best for’ describing the success/failure of specific biochemical reactions critical to human beings’ survival, then one would be able to ascertain exactly what type of and how much effort would be needed to ensure habitability. And once the above has been identified, a follow-up step would be to test another series of microbes to see which micro-organisms would be most efficient at altering/ameliorating some particular biochemical parameter to get the alien ecosystem right for human survival.

    Regarding our/our planet’s uniqueness … there’s been a lot of news lately about Earth-type planet discoveries, such as the cut & paste below. On a another topic/thread, Joan described how prolific, adaptable, variable, etc. fungi are. To me, these two bits of information taken together suggest that given a habitable niche, life is inevitable. The next step in space-exploration is likely to be to determine best prospects for potential colonization based on habitability. (But before this we’ll probably need to get some baseline testing done – probably on the ISS – of candidate micro organisms.)

    http://www.sciencedaily.com/releases/2011/12/111205140525.htm

    “NASA’s Kepler Mission has discovered the first super-Earth orbiting in the habitable zone of a star similar to the Sun. A team of researchers, including Carnegie’s Alan Boss, has discovered what could be a large, rocky planet with a surface temperature of about 22 degrees Celsius (72 degrees Fahrenheit), comparable to a comfortable spring day on Earth.” …

    … This discovery supports the growing belief that we live in a universe crowded with life,” Boss said. “Kepler is on the verge of determining the actual abundance of habitable, Earth-like planets in our galaxy.”

    • Alex Tolley permalink
      December 24, 2011 3:40 pm

      “Kepler is on the verge of determining the actual abundance of habitable, Earth-like planets in our galaxy.”

      Not quite. Kepler identifies candidates for earth-like worlds. Follow up work/missions that at spectra will help to elucidate this better. Imaging will be helpful, as will a probe to the target.

      I’m hoping that within a couple of decades we will have a far better grasp on the question of whether the universe is life bearing or not.

      The difficulties are obvious – we cannot determine if Mars has life from our observations, even probes (Viking) failed to settle the question. Europa is even worse.

  8. December 24, 2011 8:56 pm

    “All we have to do is seed a planet with cyanobacteria, and there will be oxygen and organic soup soon enough.

    “Soon enough” being how long exactly?”

    Well, within a day, if the water is dilute without too high a concentration of metals. To have an oxygen atmosphere all around the planet might take longer, maybe a hundred years based on gas cycling rates here. That’s a stretch for anyone to say.

    “I think the universe is full of life”
    Yes it’s a belief, but there are good statistical arguments for it. More later.

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