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The Odds on Interstellar Panspermia

Our recent look at panspermia concepts was largely devoted to the transmission of life via microbes or spores here in our own Solar System. The even richer question of how life might pass from star to star is far more problematic, but as a follow-up to that earlier story, I want to look at work that graduate student Jess Johnson did with Jonathan Langton and advisor Greg Laughlin at the University of California, Santa Cruz. Their work suggests that while life might readily survive an interstellar journey, it is unlikely to wander close enough to seed another system.

Ponder the era here on Earth known as the Late Heavy Bombardment (LHB). After the period of planetary accretion ended some 4.4 billion years ago, life apparently began. But 3.8 to 4 billion years ago, the LHB saw the planet again pummeled, causing debris to be ejected into space. Looking specifically at the mass that is ejected at 16.7 kilometers per second in the direction of the Earth’s motion (this is Solar System escape velocity), Johnson, Langton and Laughlin found that a substantial amount of rock (about 5 X 1021 grams) would have been blasted free of the Sun.

Remember, this is a period after life has started, so biological material could presumably be involved in any materials lifted into space. But what could survive the 20,000 g’s the ejecta would have experienced, and then cope with vacuum, radiation, cosmic ray strikes and ultimate re-entry and collision upon arrival? Bacillus subtilis is a common bacteria that needs no oxygen to survive, uses carbon and nitrogen as nutrients and forms spores when it lacks the nutrients to thrive. The dormancy period we’re talking about runs into the tens of millions of years, obviously long enough for an interstellar journey — even our glacially slow (by interstellar standards) Voyager spacecraft could make it to the Centauri stars in 75,000 years or so if they were pointed in that direction.

Here’s a striking fact: A viable sample of Bacillis has been found in the stomach of a mosquito encased in amber that has been dated at 25 million years old. Moreover, Bacillus passes all the other tests, able to survive impact pressures upon arrival, capable of enduring 33,800 g’s and, shielded by a sufficient outer encasement of rock, more than able to withstand the radiation hazards of the journey. In deriving the amount of ejected materials (the 5 X 1021 grams mentioned above), the Santa Cruz team chose only those fragments of rock greater than one metre in diameter to ensure the necessary shielding.

So everything looks promising for interstellar panspermia except the possibility that such life-bearing rocks may make their way to another stellar system. Producing calculations on the odds of capture, the trio found a result discouraging for interstellar panspermia theorists:

The results of our work found that, although there are microrganisms that are easily capable of surviving all of the challenges of interstellar travel, the probability of capture by another planetary system is vanishingly small. It should be noted that this in no way negates the possibilty of transport between worlds in our own system, a situation that seems quite possible.

A poster on this work (though without the later results) can be found here.

Related: An upcoming paper by William Napier and Janaki Wickramasinghe (Cardiff Centre for Astrobiology) in Monthly Notices of the Royal Astronomical Society discusses the Solar System’s movement through the plane of the galaxy, suggesting that the chances of comet collision go up every 35 to 40 million years. The potential for disaster on Earth is obvious, but the paper argues that such impacts help life to spread. Says Chandra Wickramasinghe, the Centre’s director, “This is a seminal paper which places the comet-life interaction on a firm basis, and shows a mechanism by which life can be dispersed on a galactic scale.” Wickramasinghe collaborated with Fred Hoyle in the 1981 book Evolution From Space. More in this news release.

Comments on this entry are closed.

  • Paul F. Dietz May 5, 2008, 14:30

    Do the odds of capture include capture into protostellar systems? I imagine rocks will be captured more easily if they encounter a dense gas disk (and then later accrete onto a planet) than if they have to directly strike a planet while passing through the system.

  • Administrator May 5, 2008, 14:51

    Paul, that’s a good question. I just had a note from Greg Laughlin saying that he and Jess Johnson had the panspermia work on the back burner for the moment but that they intended to resume it down the road. I’ll drop him a note re your question and see if he has a comment.

  • dad2059 May 5, 2008, 16:40

    If you’re talking about natural interstellar seeding, then yes I can see the difficulty of it.

    But what about directed panspermia?

    What would the technical hurdles need to be jumped to accomplish a project like that?

  • Heresiarch May 5, 2008, 19:37

    As for the participation of protostellar nebulae, have a look at the Silicon and Biogenesis page at http://www.starlarvae.org

  • Zen Blade May 5, 2008, 22:06

    I was at this great symposium on Thursday/Friday

    I have pages of notes. Just thought I would post in a relevant thread.
    -Zen Blade

  • John Hunt May 5, 2008, 22:06

    Dad2059 asks about the technical hurdles needed for directed panspermia. As I think about that question I don’t know but think that directed panspermia is possible and would have success even given current technologies.

    The good news of the shielding, viability, and re-entry survival of spores for natural panspermia would still apply to directed panspermia. It seems as though the challenge is more one of:
    – ensuring that the initial course was spot-on,
    – sufficient power is available during the mid- and terminal flight phase, and
    – that terminal course adjustments were made.

    So imagine that we have a craft with a transponder. It could use a magnetic sail and/or ion engine for propulsion. With the transponder we get precise course meansurements. Its ion engine could be fired perpendicular to it’s course for fine course adjustements. So as it leaves the neighborhood of the solar system it is traveling on a pretty precise course and at a speed that means it would make it to a destination star system in something like 15,000 years (288,000 km/hr). As it travels in interstellar space the position of the target star would change relative to distant stars if the craft were slightly off course. If so, it could fire its ion engine perpendicularly and make adjustments.

    Making terminal course corrections would be critical to the success of the mission. If properly shielded and with the frozen preservation of deep space I think that an ion engine might still be able to function after 15,000 years. Alternately, frozen simple chemical propellants might be able to be preserved over this time span. I think that a simple imaging system could still work at this time frame if properly shielded and a properly chosen radioactive power source would provide sufficient energy to run the camera and ion engines. Also, as the craft came to the target star then previously shielded solar panels could be deployed which would provide all of the energy necessary. So I think that directed panspermia is within today’s capability.

    But I see another problem; one of sufficient justification. Easily within 1,000 years we would be able to send seeding craft to the target star at far greater speeds than we are able today. So today’s craft would be unjustified because it would be outrun by later craft. What then would be the justification for initiating panspermia today?

    This issue of motivation is something that I think we interstellar mission advocates need to address head-on. A panspermia mission today would be unjustified for the reason mentioned above…unless we won’t survive long enough to launch faster missions. Given our advances in nanotech, biotech, high-energy experiments, and AI it is a possible fate which seems plausible. So a panspermia launch today would be insurance against the possibility that we might not be around tomorrow. But I think that it would be a poor consolation prize. Human civilization is destroyed but at least we seeded a nearby star system with bacteria setting us back “only” a few billion years. Given the life span of solar systems, that system may not have enough time to evolve an intelligent civilization.

    Rather, I think that such a mission only becomes justified when we are able to send human seeds with the ability to quickly establish a human colony. Could frozen embryos be viable after being frozen for 15,000 years? Possibly. Do we today have the technology to gestate the first human couple? Probably not but it does seem within reach with a few decades of work.

  • ljk May 5, 2008, 22:27

    Heresiarch, I say they haven’t gone far enough.

    I am willing to bet that entire galaxies are living beings,
    though of course not quite of the same kind of living
    creatures as we would initially recognize, being so small
    and deeply embedded in one of them.

    But they do consume one another and the larger ones
    seem to “reproduce” by merging with each other. Maybe
    that is what the Milky Way and Andromeda are on their
    way to doing.

    Carl Sagan once said we are a way for the Universe to
    know itself. Perhaps like one of the larger dinosaurs, a
    very large galaxy needs numerous “brains” (ETIs)
    scattered about to fully know itself.

    Maybe the entire Universe is alive….

    Puts a whole new spin on SETI, doesn’t it?

  • Adam May 6, 2008, 15:20

    Hi John

    There was work on interstellar messenger probes a few years back – the researchers’ names escape me – and they pointed out that some electronic components already have mean failure lifetimes of c. 10,000 years or so. Enough for a slow probe to easily do 10 lightyears. While vitrified cells might remain viable I’m really not sure what space radiation will do over millennia – it might be easier to encode the structure of cells into another medium and then sequence them and remake them at the destination. Perhaps direct synthesis of cells is a worthwhile project for Craig Venter and colleagues?

  • James M. Essig May 6, 2008, 22:16

    Hi John Hunt, Dad2059, and Adam;

    It seems that with the rapid pace of biotechnology, we should indeed be able to have artificial wombs that would deploy with human embryoes which could then be grown till birth upon which the humans at birth could be instructed by intellegent robots untill the humans reached maturity. All the ingeadients could be launched in pods that would become activiated when they sensed the location of a terrestrial planet. The contents could be encased in radiation shielding material and within reentry vehicles made of refractory materials with parachutes made of woven carbon fiber for chemical and mechanical durability. Upon reaching a candidate planet, the pod would enter the planet’s atmosphere and land via parachute.

    Millions if not billions of these pods could be launched to spread humanity throughout the galaxy and even greater numbers could be launched out of the Galaxy to other galactic locations with the ultimate net effect of spreading human life throughout the cosmos. However we do directed transpermia, if we go extinct here on Earth, or even in the event of the risk of such occuring, directed transpermia may ensure that the legacy of humanity and the meaning of our presence in the cosmos is not lost. I have hope that we will survive to do manned interstellar travel, but the risk of the unthinkable occuring might give us grounds, politicallly, to consider the prospects of directed transpermia.


    Your Friend Jim

  • forrest noble May 8, 2008, 1:36

    Hey Jim, Adam

    I think that panspermia from intra-galactic clouds is one real possibility for the origin of life on Earth. If beginning life started in dense, moist, warm clouds of organic matter then there would be a good chance we’ll eventually find it all over the place. This was Fred Hoyle’s hope who was one of the originators of this theory. I think most all of us space nuts would want to find life dispersed everywhere.

    If this were locally true there would be a common ancestor. And the life that we might find in our own solar system or the solar system of neighboring stars might all be recognizable as DNA/ RNA carbon based life.

    Jim, preserving human life would certainly be a popular goal.

    your friend forrest

  • george scaglione May 8, 2008, 13:20

    forrest,yes a very interesting way of looking at things…life like ours might indeed be relatively “common” if we look at it that way!and as i have already mentioned to jim,i unfortunately do not give much creedence to his above theory.i know that preserving human life would be a popular goal but i see that as being accomplished over the centuries by human expansion out into the galaxy/universe by means of,at first at least,ships.(!) have been having some interesting conversations in that regard about types of propulsion that might be used lol pretty much from “soup to nuts”would be glad to expand on that or hear others ideas/opinions next time i come on line.but for now everybody,all the best your friend george

  • John Hunt May 8, 2008, 19:43

    This is exciting.

    If electronic components can function after thousands of years then this simplifies many of the challenges of interstellar flight.

    With lower velocities we don’t need all of the beamed propulsion architecture (e.g. lasers, particle beams, large solar panels, etc) nor large quantities of He3. Shielding from micrometeorites becomes much less of a problem. Also deceleration requirements are lower. I believe course adjustment also becomes easier.

    However, as mentioned before, a slow-boat mission cannot be justified on a discovery basis as later faster craft would overtake earlier launched craft. It could only be justified on a “survival of humanity basis”.

    Unfortunately this increases the mission complexity significantly as we’d be talking about preservation of cells, gestation, life support and rearing. Not easy but within reach.

    Adam’s suggestion of getting a Craig Venter going on the biologic side of the mission is therefore an excellent idea. Venter, Elon Musk, & others seem open to the idea of directing their effort & wealth towards projects that they feel humanity needs in order to survive risks. Offer as matching funds and it could attract govt & other private funds.

    Conceivably we can offer an interstellar mission plan that uses today’s craft technology and 2035 biotechnology and could be done for roughly $50 billion +/-. The rationale would be reasonable in that it is:
    – insurance against existential risks (a real possibility),
    – would advance today’s space and biotech technology,
    – provide educational inspiration for math, physics, and biology, and
    – unite countries in a project on behalf of humanity.

    What is needed now is for a technical design of such an interstellar mission by specialists of the various relevant fields (including ethics and policy). I would like to request that Tau Zero Foundaton consider such a design for all of the reasons mentioned above.

  • ljk June 16, 2008, 9:59

    Genetic building blocks may have formed in space

    NewScientist news service June 13, 2008

    Ring-like carbon molecules that are
    essential for the creation of
    nucleic acids like DNA and RNA might
    have formed in a meteorite called
    Murchison before it landed in
    Australia in 1969, according to Zita
    Martins, a chemist at Imperial
    College London. The Murchison
    meteorite (Chip Clark/Smithsonian
    Institution) The ratio of carbon-13


  • Sean Taylor August 18, 2008, 21:17

    The idea of a directed panspermia project in the near future is interesting from a science and engineering perspective, but philosophically it seems a bit silly. Considering that almost every realistic near-term extinction threat is of our own making, it makes a lot more sense to devote our resources to ensuring that we don’t destroy ourselves rather than wasting resources shooting our DNA into space. If we can’t avoid destroying this planet, isn’t it a bit insane to want to pollute the rest of the universe with our defective species? Sure, there are a few natural catastrophes that could wipe us out, which can either be addressed directly (asteroid deflection systems), or are so powerful (e.g. gamma ray bursts) that there isn’t much we can do anyway. Fortunately the odds of the latter are very remote, so it’s not really worth worrying about. The point is, if we can’t survive and colonize space “normally”, panspermia isn’t much of a solution. It’s very difficult to care about cells that may arrive at a distant planet tens of thousand of years in the future.

  • ljk September 4, 2008, 21:25

    Natural Transfer of Viable Microbes in Space from Planets in
    the Extra-Solar Systems to a Planet in our Solar System and


    “We investigate whether it is possible that viable microbes could
    have been transported to Earth from the planets in extra-solar
    systems by means of natural vehicles such as ejecta expelled by
    comet or asteroid impacts on such planets. The probabilities of
    close encounters with other solar systems are taken into
    account as well as the limitations of bacterial survival times
    inside ejecta in space, caused by radiation and DNA decay. “