≡ Menu

Life’s Cometary Arrival Unlikely

Life seeded throughout the cosmos makes for a satisfying vision, but what are the odds that some kind of panspermia could really happen? Rutgers researchers cast a bit of cold water on the concept recently with data showing what happens to DNA from microbes frozen for millions of years in Antarctic ice. The upshot: Radiation bombardment in the interstellar depths makes survival unlikely. That makes the Fred Hoyle-style delivery of life via cometary bombardment look improbable.

Antartica makes a good testbed for such studies because the polar regions receive more cosmic radiation than anywhere else on the planet, as well as containing its oldest ices. The DNA in the five samples studied by the research team showed marked decline after 1.1 million years. Rutgers’ Kay Bidle notes that “There is still DNA left after 1.1 million years. But 1.1 million years is the ‘half-life’ – that is, every 1.1 million years, the DNA gets chopped in half.”

Bidle’s team doesn’t completely rule out life being transferred among planets within the Solar System, but finds it unlikely that life on Earth could have arisen from extrasolar sources. Somewhat lost in the shuffle is the impressive news that DNA frozen in glaciers may return to life with glacial melting even after vast periods of time. The team sampled and melted ices ranging from 100,000 to eight million years old looking for microorganisms that had been trapped within.

And find them they did. As expected, the microorganisms from younger ice grew more quickly than their older counterparts. And those in the oldest ice couldn’t be identified at all because of the deterioration in DNA. The ices came from two valleys in the Transantarctic Mountains, a remote and hostile place that reminds us of the incessant mutability of living things, something to be kept in mind as we ponder potential habitats on other planets both in our system and beyond.

The paper is Bidle, “Fossil genes and microbes in the oldest ice on Earth,” published online on August 8 by Proceedings of the National Academy of Sciences (abstract). I’ll post the print reference when it becomes available.

Comments on this entry are closed.

  • mz August 10, 2007, 19:00

    Why not?
    Assume a 100 ly distance. 30 km/s speed for the comet (via some fancy gravity slings), that is 1E-4 c. Thus 100 ly will take 1 million years to travel. That’s about 1 “halving”. Could that not serve as basis for life?

    Seems that 210 pairs out of 3 million is little, but isn’t the arising of life by chance from non-self-replicating also pretty unlikely and would require quite a long chain of events.

  • Stephen August 10, 2007, 19:12

    There was a story some years ago that microbes trapped in amber were revived after some 37 million years, leading to the idea that at least some microbes are immortal.

    Life in general is immortal. But it uses lots of copies, and constant vigilence. In panspermia, one would think that only a modest number of copies and no regrowth would be possible during the trip. How likely is one of these assumptions wrong?

    This ‘half life’ is an odd thing. It’s pretty amazing that a microbe with it’s DNA cut into 210 base pair lengths would continue living at all. Some hardy microbes might manage to repair it. For panspermia, it only takes one.

    The summary suggests that they think the damage is due to cosmic rays. But we may have to wait for the paper to see if they think some of the damage could have been due to ice, or other material issues over the vast stretches of time.

    How deep in a chunk of rock would a microbe have to be in order to be safe from cosmic rays? Probably alot. Last i heard, if you want to detect cosmic rays, you go underground – to avoid detecting other stuff. How can an astronaut orbiting the Earth detect cosmic rays? They close their eyes and look for flashes.

    Interesting article. 1.1 million years isn’t that long for getting stuff to/from Mars, much less other stars. I still expect Mars life, related to Earth life, will be found. We’ll probably argue about forward contamination for eons, unless Mars life is found that is adapted to hydrogen peroxide soils, or something.

    Forget panspermia. Intersteller travel is looking real difficult. Cold sleep may not be an option. Humans don’t repair DNA very well compared with microbes, and have long gestation times. Further, you want all sorts of other stuff – plants, other animals, etc. Perhaps the easy way to do it is to send a robot ship that can create life from material at the destination. Maybe DNA (etc.) codes could be sent by radio on arrival, so evolution could start with the latest.

    The Fermi paradox: where are they? They stayed home. Leaving home is brutal.

  • Stephen August 10, 2007, 19:20

    isn’t the arising of life by chance from non-self-replicating also pretty unlikely and would require quite a long chain of events.

    The evidence is that life on Earth sprang up approximately the instant that it could survive. Give or take a million or so years. That suggests life starts easily. The latest ideas on how it might have happened are interesting. Starting with DNA is hard. Starting with RNA is hard, but not nearly so bad. There are noises that there is much, much easier chemistry available that might lead to RNA life, which then might lead to DNA life. I’m not a chemist, and so can’t relate the story.

    I wouldn’t risk my faith by having it depend on science never figuring this out.

  • enzo August 11, 2007, 6:32

    The fact that they found viable microorganisms after 8 Myrs is good news for Phoenix, just launched to Mars :

    As the article above points out (at the end), models indicate that Mars polar regions get a lot warmer every 50 Kyrs or so due to the instability of the tilt of the rotation axis (up to 40 degrees from the current 25).
    Phoenix might find something really interesting in the polar ice.


  • Christopher L. Bennett August 11, 2007, 11:21

    I think these findings are premature. My main question is, what is the source of these microbes frozen in the ice? Different forms of life have different degrees of radiation resistance. Some species of microbe are far more resistant to radiation than others, because they’ve evolved in radiation-rich environments. Now, we’ve discovered there are microbes that thrive in the upper atmosphere, lifted there by air currents and magnetic fields. They live in conditions of near-vacuum and relatively hard radiation, and because of that, they’ve evolved to be able to withstand such conditions. I very much doubt that’s true of the kinds of microbes that you’d find frozen in a polar icecap.

    But the kinds of microbes that would be candidates for panspermia are the upper-atmosphere ones, the ones that sometimes get pushed clear into space by the Earth’s magnetic field. So they’re the ones whose viability we should be testing. I don’t think these results count for much, because they’re testing the wrong population of microbes.

  • Adam August 12, 2007, 2:11

    Hi All

    To properly comment I’m waiting for the paper, but a few points can be made:

    (1) The microbes were in biostasis – frozen or immobilised in the ice. Thus no repair against radiation damage. Cumulative damage means that even organisms like Deinococcus radiodurans would be at serious risk after sufficient time.

    (2) While living things, on and under the Earth, are continually bathed in muons produced by cosmic rays the main damage comes from natural radioactive decay of things like uranium, thorium and potassium. Potassium, as its isotope K-40, is quite radioactive and would be deadly for humans preserved cryonically over sufficient time periods. Living things cope by continual self-repair, but preserved/biostatic life-forms are degraded inexorably.

    None of that means life can’t travel between the stars – it just has to travel quickly and/or have some continual repair mechanism available. Quite a tall order to maintain repair at the cryogenic temperatures an interstellar comet is expected to fall to.

  • Alastair McKinstry August 12, 2007, 14:43

    It looks like this experiment is timely:


    A Scottish rock (with microbes embedded) is to be attached to the outside
    of a Foton M3 mission, re-entering Earth 2 weeks later.
    Lets see if the microbes survive.

  • Paul Dietz August 14, 2007, 14:47

    The evidence is that life on Earth sprang up approximately the instant that it could survive. Give or take a million or so years. That suggests life starts easily.

    This strikes me as begging the question. An alternative explanation would be that life arrives from space quite often, so it establishes itself as soon as conditions on the planet are conducive. The actual origin of life from non-living matter could still be quite rare.

    I have wondered if very young star systems, with lots of gas available, would be more friendly for interstellar panspermia, with the gas slowing and capturing passing life-bearing rocks and comets. This capture could have a far higher cross section that capture directly onto a planet. We could then imagine the microorganisms incubating in smallish planetoids, heated by radioactive decay, that had liquid water in their interiors, and only later being transfered to newly formed larger planets.

  • Ron S August 14, 2007, 16:45

    Assuming life arises rarely and that the gas cloud out of which our solar system and other sister systems is good at capturing life-bearing rocks and comets, the likelihood of panspermia still seems remote to me. The reason being that with life being rare there are a small number of point sources in the galaxy from which the life-bearing material could be ejected, and it spreads with an r^2 law, the solid angle of interception even of a several ly wide cloud is quite tiny.

    If we keep the same scenario but assume more panspermia sources, that is, life is not so rare, we may as well more simply assume life arose locally.

    This is admittedly a hand-waving argument since I have not made a calculation.

    Another possible argument against panspermia is the assumption that early Earth is a welcoming environment for whatever organisms or interesting molecules happen to arrive. My guess is it’s easier if the material is very primitive (pre-DNA) and much, much harder at the scale of cellular organisms. Higher-order organisms seem to have a narrower comfort zone.

  • MaDeR August 15, 2007, 7:30

    “The evidence is that life on Earth sprang up approximately the instant that it could survive. Give or take a million or so years. That suggests life starts easily.”

    … or this beginning moment is only moment that allows for abiogenesis.

  • Paul Dietz August 15, 2007, 11:16

    … or this beginning moment is only moment that allows for abiogenesis.

    Or that life had originated on Earth, then some had been ejected into solar orbit by impacts, and after the last Earth-sterilizing impact some of that ‘saved’ life was redeposited and immediately recolonized the planet.

  • ljk August 15, 2007, 11:18

    Did Life Begin In Space? New Evidence From Comets

    Science Daily August 14, 2007


    Recent probes inside comets show it
    is overwhelmingly likely that life
    began in space, according to a new
    paper by Cardiff University Centre
    for Astrobiology scientists. They
    suggest that radioactive elements
    can keep water in liquid form in
    comet interiors for millions of
    years, making them potentially ideal
    “incubators” for early life. They…


  • Paul Dietz August 15, 2007, 11:21

    The reason being that with life being rare there are a small number of point sources in the galaxy from which the life-bearing material could be ejected, and it spreads with an r^2 law, the solid angle of interception even of a several ly wide cloud is quite tiny.

    When I plug plausible numbers into this argument I don’t seem to reach the same conclusion as you do. Perhaps you could be more explicit?

  • Ron S August 15, 2007, 20:06

    “Perhaps you could be more explicit?”

    Well, I can try, provided you understand that I am no expert and there far too many assumptions that need to be made. Where I provide numbers feel free to substitute others. Hopefully I capture at least the quality of the scenario even if I make errors. I’ll take criticism as an opportunity to learn! I am also doing this in a vacuum by not reading up on relevant writings on this topic.

    If life is rare there is a large ratio of nebulae to life-bearing planets. However I will look at this from the perspective of the target (e.g. Earth), not the source. The reverse scenario is the same but with multiple opportunities per ejection event.

    Let’s say there are 100 life-bearing planets in our galaxy (rare). If we accept there is a GHZ with Earth at the proper radius we can place these planets equally spaced in a circle with that radius. That puts them 2,000 ly apart along the arc. A 10 ly wide nebula (out of which systems like our own are born) at this distance is about a millionth area patch of sky from the source. The impact of the bodies causes ejection of material. It isn’t isotropic, but assuming there are many we can on average assume isotropism. Not all of the material bears living material and not all of it exits the source system. Of what does, about 1 mg per kg of ejecta strikes the nebula. With the expected relative velocities we can assume most is slowed and captured. Only a portion of the nebula collapses into stellar systems, but how much I’m not sure.

    Travel time matters. If chemically stable, there is the half-life due to cosmic rays to consider. The further the source is from the target nebula the fewer living molecules survive. Simpler molecules likely do better, so this allows more viable sources per target.

    Now there are two major possibilities. If the ejecta accretes into a forming system it is most likely to end up in the star or a gas giant plant rather than a rocky planet in the star’s HZ. Even if it accretes to that planet will almost certainly end up in the interior, not on the surface where we want it. Also, the surface will likely be hostile to the molecules of interest, reducing them chemically or thermally. Not good.

    If the ejecta encounters a newly formed system that is mostly cleared of gas and dust, and with reasonably stable rocky planet surfaces, accretion is more difficult. Presumably it get slowed at the boundary where gas and dust are more prevalent, perhaps the forming Oort cloud, and from there, like comets, the ejecta gradually drops down to be in part captured by rocky planets in the HZ. Most would end up hitting other bodies.

    At this point in the story we have a fraction of the life-bearing ejecta raining down on Earth or a similar planet at just the right time and place to allow a relatively short interval between ejection event and capture, and with the timing of suitable nebula and system formation just right for our purposes. Now the molecules hit the surface of our planet either by rock disintegration in the atmosphere or by becoming a meteorite.

    The molecules that survive are likely not at the surface of the rock, so we need some erosion to release them. Will they survive when they finally enter the environment? They could be reduced immediately (as above) or drop into a pond, clay, ice or other good environment where the molecules can revive, find raw materials and reproduce. These have to be simple enough that their food is mineral in nature and not a byproduct of other organisms.

    To summarize, this can all happen as described. I didn’t show actual probabilities since I don’t think I can defend specific numbers and quantities. However the quality of the scenario leads me to believe that the probability of success is simply too low. I can more easily believe that these very same viable molecules can evolve on the planet at a time and place hospitable for it to occur.

  • ljk August 17, 2007, 14:30

    Scientist: Calculations Prove Life Began in Comet


    Critics say the evidence is faulty.

  • ljk August 17, 2007, 15:00

    Fiery rock will test whether life came from space

    The rock – formed from lake sediment – will be launched on a rocket and subjected to the blast of re-entry to see which molecules of life survive.


    And the Vostok flies on:


  • Ron S August 17, 2007, 16:27

    “Critics say the evidence is faulty.”

    Looks to be more correct that critics say there is no evidence and therefore it’s a calculation based on speculation. I like this quote in the article: “Chandra Wickramasinghe, an astrobiologist at Cardiff University in the United Kingdom, and his team say their calculations show that it is one trillion trillion times more likely that life started inside a slushy comet than on Earth.” Quite the claim.

  • ljk December 11, 2007, 17:41

    To quote:

    Catching a free ride to Mars takes more than sticking out a thumb, but some hardy Earth bacteria could survive as hitchhikers clinging to the outside of spacecraft, studies have shown.

    Now a set of experiments going up with space shuttle Atlantis to the International Space Station will test how exposure to the harshness of space might change bacteria during a simulated Mars mission.

    The current shuttle experiment—a collaborative effort between the University of Florida, NASA, the European Space Agency and the German Aerospace Center (DLR) in Cologne—will take place for more than a year on an external space station platform called EXPOSE. That platform will be installed outside of ESA’s Columbus laboratory module upon delivery by space shuttle Atlantis flight STS-122.

    Full article here:


  • ljk January 14, 2008, 10:22

    Radioactive Hot Spots on Earth’s Beaches May Have
    Sparked Life

    Written by Ian James O’Neill

    We’ve heard about life being created in a puddle of
    primordial chemical soup, sparked by lightning strikes,
    or organic molecules falling to Earth from comets or
    planets, such as Mars.

    But now, there is an alternative. Early Earth was radioactive;
    the Moon also had a lower orbit, generating strong tidal forces.
    Due to the close proximity to abundant water, radioactive
    beaches may have possessed all the essential ingredients
    for organic compounds, and eventually life, to thrive.

    Research by the University of Washington, Seattle, suggests
    that perhaps the highly radioactive environment of Earth
    some 4 billion years ago may have been the ideal time for
    life to form. The orbit of the Moon also had a part to play in
    this offbeat theory.

    Full article here:


  • ljk January 23, 2008, 11:40

    Space Roaches Develop into Super Mutants

    Maybe it’s time to welcome our new insect overlords. In what sounds like the prequel to the movie Alien, Russian news Agency Novosti, reported on an experiment involving baby cockroaches conceived aboard a satellite in back in September. Apparently, they found, a trip to space gives roaches “superpowers”.

    The cockroaches conceived in space onboard the Russian Foton-M bio satellite have developed faster and become hardier than ‘terrestrial’ ones, a research supervisor confirmed on Thursday.

    The research team has been monitoring the cockroaches since they were born in October. The scientists established that their limbs and bodies grew faster.

    “What is more, we have found out that the creatures… run faster than ordinary cockroaches, and are much more energetic and resilient,” Dmitry Atyakshin said.

    The full article here:


  • ljk April 30, 2008, 11:55

    The Peculiar Volatile Composition of Comet 8P/Tuttle: A Contact Binary of Chemically Distinct Cometesimals?

    Authors: B. P. Bonev, M. J. Mumma, Y. L. Radeva, M. A. DiSanti, E. L. Gibb, G. L. Villanueva

    (Submitted on 29 Apr 2008)

    Abstract: We report measurements of eight native (i.e., released directly from the comet nucleus) volatiles (H2O, HCN, CH4, C2H2, C2H6, CO, H2CO, and CH3OH) in comet 8P/Tuttle using NIRSPEC at Keck 2. Comet Tuttle reveals a truly unusual composition, distinct from that of any comet observed to date at infrared wavelengths. The prominent enrichment of methanol relative to water contrasts the depletions of other molecules, especially C2H2 and HCN. We suggest that the nucleus of 8P/Tuttle may contain two cometesimals characterized by distinct volatile composition. The relative abundances C2/CN, C2/OH, and CN/OH in 8P/Tuttle (measured at optical/near-UV wavelengths) differ substantially from the mixing ratios of their potential parents (C2H2/HCN, C2H2/H2O, and HCN/H2O) found in this work. Based on this comparison, our results do not support C2H2 and HCN being the principal precursors for respectively C2 and CN in Tuttle.

    The peculiar native composition observed in 8P/Tuttle (compared to other comets) provides new strong evidence for chemical diversity in the volatile materials stored in comet nuclei. We discuss the implications of this diversity for expected variations in the deuterium enrichment of water among comets.

    Comments: Accepted for Astrophysical Journal Letters

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0804.4673v1 [astro-ph]

    Submission history

    From: Boncho Bonev [view email]

    [v1] Tue, 29 Apr 2008 18:29:28 GMT (321kb)