“Since stars appear to be suns, and suns, according to the common opinion, are bodies that serve to enlighten, warm, and sustain a system of planets, we may have an idea of the numberless globes that serve for the habitation of living creatures.” -William Herschel

When you look up at the stars in the night sky — bright and dim, young and old, near and far — can you help but wonder which ones of them might house life of any variety? And if so, how similar or different it might be from that on Earth? It’s one of the greatest as-of-yet unanswered questions in all of science.

Illustration credit: NASA / FUSE / Lynette Cook, via http://imagine.gsfc.nasa.gov/docs/features/bios/roberge/roberge_image.html.

Illustration credit: NASA / FUSE / Lynette Cook, via http://imagine.gsfc.nasa.gov/docs/features/bios/roberge/roberge_image.html.

And yet, PZ Myers is at it again, reducing the whole thing to some silly “absurd astronomers vs. intelligent, nuanced biologists” meme, like so.

Image credit: PZ of Pharyngula.

Image credit: PZ of Pharyngula.

The thing is, we can be honest about what we know and what we don’t, and make reasonable conjectures about what we think there is to find out there.

When all is said and done, what do we think are the prospects for alien life in our galaxy? Go read the whole thing!

Comments

  1. #1 Chad Orzel
    July 2, 2014

    To be fair, that graphic doesn’t originate with Myers. It’s from this Praxtime post, as far as I can tell.

    (My comments are here, as long as I’m posting links…)

  2. #2 Kenny A. Chaffin
    July 2, 2014

    Great stuff Ethan, thanks. I wrote a short (much less detailed) blog post in this vein late last year. To the Stars!
    http://kennyachaffin.blogspot.com/2013/03/to-stars.html

    I’m hoping we discover at least simple non-terrestrial life while I’m still around…..unless of course we hit the singularity and all live forever. :)

    Love your work. Thank you!

  3. #3 eric
    July 2, 2014

    Two interesting thoughts. First, if life on earth did arise somewhere else, then the question of origins of life just got a lot harder to answer. All those experiments where we try to simulate the conditions of the early earth and combine organic molecules that would’ve been present could be drastically wrong.

    Second…

    And finally, if we look and figure out that we are alone… am I the only one who feels like it’s humanity’s duty and responsibility to do what no one else can in this Universe, and extend our civilization to stars beyond our own?

    I think many scientists have inconsistent or contradictory feelings about this. I bet that, as an abstract thought, many would probably agree with you that, yes, this is a good idea. OTOH we spend an awful lot of effort ensuring our probes do not contaminate mars, venus, titan, etc.. with earth-life, don’t we? Given that there is practically no chance that we could visit worlds in other solar systems and confirm they are without native life before we ‘panspermiated’ our own forms of life, these two facts seem logically inconsistent. If we have no problem seeding worlds in other solar systems with primitive earth life amidst uncertainty over whether it might wipe out native forms of life, then we should have no problem seeding mars or io or any other solar system body admidst some uncertainty that it might wipe out native forms of life.
    The same inconsistency can be pointed out if one makes a knowledge-based or environment-based objection to changing (for example mars). We want to wait until we know more about its natural state, before ruining? That argument applies to other planets too. We don’t want to change its natural environment? That argument also applies to other planets.
    Its almost a bell-the-cat situation. A belled cat (life spread to other planets) sounds like a really nice end state, but when the bell arrives in the mail, all the mice get the feeling that trying to actually hang the bell around the cat’s neck would be a really bad idea.

  4. #4 John H
    July 2, 2014

    The fly in both ointments is that the solution to the Fermi paradox might be that it could be beyond the ability of any technological civilization to travel interstellar distances. Perhaps the attempt to do so turns out to be economic suicide, or perhaps just simple suicide, or perhaps just not worth the effort. And Myers’ characterization of what’s out there as an “ecosystem” to be inevitably filled is as fanciful as any hand waving space opera future proposed by the starbound believers. At least the strawman astronomer has reason to believe the rest of the universe works the way he thinks it does, while his PZ’s avatar has only the evidence from one very small corner.

    I prefer Orzel’s take on it – not enough data to even begin to think we can make reasonable guesses about this particular question.

  5. #5 Omega Centauri
    July 2, 2014

    There is so much we don’t know about what sort of planets are needed for complex life. There are lots of rocky planets in the habitable zone of red dwarfs, but they are tidally locked. Does that preclude complex life? Does a planet need a large moon to stabilize its rotation axis? How about the flux of comets and asteroids, what conditions allow it to be low enough to reduce the number of extinction causing impacts?

    What is the ideal metalicity to form rocky planets that aren’t too big? Is the sun too metal rich, and we were just lucky, or does it really require z>=.01?

    What about chemical recycling? Do we need plate tectonics, or do other types of chemical recyling exist that might keep the surface chemistry compatible?

    So beyond the biological/evolutionary uncertainties, we also have astrological geological and climate unknowns.

  6. #6 abas
    July 2, 2014

    I think the problem is we think linear.
    According to law of Accelerating Returns(!) a civilization will fill its galaxy a few centuries after reaching the singularity (becomes type 3 or higher civilization), so we can assume:
    1. we are the most advanced species in our galaxy yet or
    2. they tend to self destruct or
    3.they follow other paths unknown to our limited since yet.
    I vote for scenario 1.

  7. #7 Cosmonut
    July 2, 2014

    I think its quite likely that the there are thousands of technological civilizations in our galaxy right now.

    The Fermi paradox isn’t really a paradox – it assumes that some civilization will set out to settle the entire galaxy – and sustain the drive to do so for millions of years !!
    (I am assuming that warp drive, hyperspace jumps and suchlike are fantasy, as they indeed appear to be)

    But just imagine a model where every time a civilization reaches another star system, there a 50 – 50 chance that it decides not to continue their journey.
    Then there is only a one in a million chance that they will settle more than 20 star systems !

    I suspect that moving to another star only happens under extreme pressure – the solar system can sustain us for billions of years for example – so the decision not to continue is much more like 99%.
    Hence, the “inevitable colonization of the galaxy by some civilization or other” is actually incredibly unlikely.

    People talking about colonizing the galaxy and deriving paradoxes are basically stuck in cowboy mode.
    Our galaxy isn’t the American wild west – its far more wondrous and also far far more inaccessible.

  8. #8 Cosmonut
    July 2, 2014

    Incidentally, I tend to find biologists rather resistant to the idea of life – especially complex and/or intelligent life – elsewhere in the galaxy.

    I sometimes suspect they don’t like the idea that their entire discipline is merely the study of one case among billions. :)

    Or maybe I’ve been talking to the wrong kind of biologist

  9. #9 G
    July 6, 2014

    Ethan, beliefs about whether or not there are other intelligent civilizations out there, are not logically bound to beliefs about whether we should or should not migrate to the stars.

    If we are the only ones, we should migrate to the stars.

    If we are only one among many, we should also migrate to the stars.

    The estimated usable lifespan of our star (another half billion years before it boils the oceans) is an infinitesimal compared to the estimated usable lifespan of stars in our galaxy as a whole. The entire history of life on Earth adds up to something comparable to seven days in the average lifespan of a human.

    I believe that natural selection works on a cosmic scale. Successful planetary lineages persist by seeking out new planets and new stars to continue their existence. They are the darwinian successes. Planetary lineages that do not seek new planets & stars are wiped out when their stars expand, explode, or die out. They are darwinian failures.

    The question for humanity is, which shall we be?

    Rogue planets provide an answer to the moral/ethical issue of migrating to planets with existing life. Rogue planets have the necessary materials but lack the energy sources to support life. They can reasonably be assumed to be dead. An advanced civ can build Dyson rings of solar collectors around a number of stars that are “near enough” to one or more rogue planets, and convert the energy to laser light, to provide energy to power life on newly-inhabited rogue planets.

    Each such rogue planet would have multiple stars to support it, and each star would support multiple rogue planets. This configuration is the most robust scenario for long-lasting planetary civilizations.

    BTW, if someone else has published that proposal elsewhere, I’d love to know where. And if not, then what reasonably respectable journals would be appropriate for submitting an article?

    —-

    Re. Kenny @ 2: “immortality via The Singularity.” That’s religion, not science, and it should be properly labeled as such. If you can reincarnate into a computer, you can also reincarnate into a cat. If I was inclined to believe in reincarnation, I’d choose the cat.

    Re. Abas @ 6: “Accelerating returns” does not account for civilizations that have overcome the instinct for exponential growth. Overcoming that instinct is essential for achieving a sustainable civilization on the original home planet. Sustainability is a precondition for having sufficient time & resources for a space program that leads to interstellar migration. A given civilization might only seek to achieve steady-state persistence. It could do that by spreading out across a radius of approx. 4,000 LY (assuming that gamma ray bursters’ destructive radius is approx. 3,600 LY, per present hypotheses). That is still a small fraction of space in our galaxy.

    The fact that there are so many unknowns in astrobiology, is all the more reason to devote significant resources to the search for life.

    Interstellar migration is not impossible under current science; it only requires extensions of currently-existing technologies.

    Propulsion: We already have achieved hydrogen fusion, in thermonuclear weapons. All that’s needed is controlled fusion, which is presently a well-supported area of research. This will get us propulsion systems capable of low relativistic speeds, on the order of a few percent of C.

    Habitation: We need to develop space habitats that can survive journeys of thousands of years at low relativistic speeds. This is certainly a challenge, but there is no fundamental new science or even fundamental new technology needed: only the concerted effort over long spans of time.

    Destination: Robotic probes can seek out potentially habitable planets. Again, no new science needed, only new technology.

    We can do this.

    Can and should.

  10. #10 Torbjörn Larsson
    Sverige
    July 8, 2014

    Well balanced, thoughtful article. (But the Fermi Question is too unconstrained to ever appeal to me, with an unknown likelihood for false negatives. E.g. this applies: “How can we possibly hope to draw reliable, robust conclusions about these questions with such a limited set of knowledge? The answer is obvious: we can’t.”)

    One comment:

    How can we possibly hope to draw reliable, robust conclusions about these questions with such a limited set of knowledge? The answer is obvious: we can’t.

    It isn’t quantified here, so the answer is precisely not obvious. As a counter example, general relativity was first tested with the limited sets of one Sun (twice the Newtonian refraction) and one Mercury (precession).

    People have put up simple models for life emergence akin to how we can predict AGW from an increased CO2 forcing, despite the details are complex. They do tend to support the point 1.) Simple life has a simple emergence, from our observing early appearance.

    One nitpick:

    There are 20+ independent emergences of multicellulars including 2 instances of lab generated such (takes less than 1 year with consistent forcing), diversified multicellulars include at least one instance of bacteria (a clade of cyanobacteria) and complex diversified multicellulars are some 7 instances at least.

    Oh, whereof 1 of the latter is animals, so presumably it isn’t that hard either. It is eukaryotes (mitochondrion endosymbiont) that is the unique step…

  11. #11 Torbjörn Larsson
    July 8, 2014

    @eric: More examples means a simpler problem, as always. If there are options that we can’t see, the problem is harder than if we see some of them.

    @Omega Centauri: Astrobiologists have made an observational filter, the Biological Complexity Index (see the Habitable Exoplanets Catalog site) to answer your problem. We do need to observe Europa for life to calibrate it, but that is still a reachable goal.

    Of course, that filters out observations, so we still need to look for signs of a complex biosphere (oxygenated atmosphere) to get full use of it, it’s a lousy predictor. If such worlds are too infrequent, we may not be able to see such.

    Many of your questions have tentative or complete answers already (locking, moons, impact fluxes, metalicity, plate tectonics), but I can’t respond to such a Gish gallop of questions.

    @Cosmonaut: No, you are misunderstanding. Evolution is contingent in theory, now we approach testing it. See the resurrected protein work, one of our hormone receptors have _one_ unique pathway, so we could be radically different evolved.

    @G: But the average animal species are ~1 million year, before it is speciated (whether branching or just laterally traversing an evolutionary path) or extinct. It is unlikely that we would be “humanity” within 1 million years, it may be tide to H. sapiens.

    And if we colonize, we split: too large distances, need 1 interbreeding(/generation (independent of population size!) to keep speciation from happening.

    This is more a moral question IMO: why not spread the biosphere? It spreads naturally. (I’m not implying that this is a “natural morality” theological thesis, it is just an “why break the process” empirical thesis.)

  12. #12 Torbjörn Larsson
    July 8, 2014

    I’ll add on animals that we know have living examples of such without the Hox box body plan, both ctenophores and sponges. The former are now known from sequencing to have evolved nervous systems and then muscles independently!

    Albeit they aren’t independent at the roots, evolving animals seems easier the more we look.

    But eukaryotes… If some geologists are correct on decreasing oxygen levels after the oxygenation pulse, and the toxic Hadley oceans nearly won out before cyanobacteria evolved nitrogen recycling and curbed the less efficient sulfur metabolisms, that is a race on each and every planet. Of course, superEarths will have more time as always.