I’ve been fascinated with Edward Belbruno’s work on ‘chaotic orbits’ ever since meeting him at an astrodynamics conference in Princeton some years back. The idea is to develop low-energy routes for spacecraft by analyzing so-called ‘weak stability boundaries,’ regions where motion is highly sensitive and small changes can create gradual orbital change. A low-energy route was what Belbruno used in 1991 to help the Japanese spacecraft Hiten reach the Moon using almost no fuel, a proof of concept about which the physicist said “It saved the spacecraft, and it saved my career.”
That comment came from a lecture to the Mathematical Association of America in 2009 that you can listen to here. It’s fascinating in its own right, but doubly so since Belbruno is back in the news with new findings on the idea of panspermia, and specifically that version of panspermia called lithopanspermia. In this hypothesis, elemental life forms are distributed between stars in planetary fragments created by asteroid impacts, volcanic eruptions and other disruptive events. Drifting through space, the fragments are eventually caught in another solar system’s gravity, some of them conceivably falling on worlds in the habitable zone of their star.
Image: The Sun is thought to have formed in a cluster of other stars around 4.5 billion years ago. Newly born star clusters like Pismis 24 (pictured) may be similar to the environment in which the Sun spent in its early years. Much closer to its neighbours than it is now, the nascent Solar System probably exchanged material with other planetary systems, and it is possible that early life could have spread between these neighbouring planetary systems. Credit: NASA, ESA and Jesús Maíz Apellániz (Instituto de Astrofísica de Andalucía, Spain).
Could something like this have caused life to begin on Earth? Belbruno’s work, with Amaya Moro-Martín (Centro de Astrobiología and Princeton University) and Renu Malhotra (University of Arizona) simulates conditions when the Sun was young and still a part of the cluster that gave it birth. Using simulations performed by Princeton graduate student Dmitry Savransky, the researchers applied the theory behind chaotic orbits and in particular the idea of ‘weak transfer,’ which they believe offers rocky fragments moving at low velocities a high probability of moving between close stars. In fact, they believe our system could have exchanged materials with its nearest planetary system neighbor 100 trillion times before the Sun left its native cluster.
“The conclusion from our work,” Moro-Martín says, “is that the weak transfer mechanism makes lithopanspermia a viable hypothesis because it would have allowed large quantities of solid material to be exchanged between planetary systems, and involves timescales that could potentially allow the survival of microorganisms embedded in large boulders.”
Moro-Martin adds that the work does not prove lithopanspermia actually happened, but indicates it is an open possibility, with further study needed into the question of rocky materials landing on a terrestrial planet. Could life have arisen on Earth before the dispersal of the cluster? The authors believe that it could, assuming life arose shortly after there is evidence of liquid water on its crust. From the paper on this work:
Within this timeframe, there was a mechanism that allowed large quantities of rocks to be ejected from the Earth: the ejection of material resulting from the impacts at Earth during the heavy bombardment of the inner solar system. This bombardment period lasted from the end of the planet accretion phase until the end of the LHB 3.8 Ga, i.e. it finished when the solar system was approximately 770 Myr old (Tera et al. 1974; Mojzsis et al. 2001; Strom et al. 2005). It represents evidence that planetesimals were being cleared from the solar system several hundred million years after planet formation (Strom et al. 2005; Tsiganis et al. 2005; Chapman et al. 2007). This period of massive bombardment and planetesimal clearing encompassed completely the “window of opportunity” for the transfer of life-bearing rocks discussed above and therefore provides a viable ejection mechanism that may have led to weak transfer.
Image: The researchers suggest that ideal conditions for lithopanspermia in the sun’s birth cluster, in the solar system and on Earth overlapped for several hundred million years (blue shaded area). Rock evidence suggests that the Earth (bottom line) contained surface water during a period when the relative velocities between the sun and its closest cluster neighbors (top line) were small enough to allow weak transfer to other planetary systems, and when the solar system (middle line) experienced high meteorite activity within the sun’s weak gravitational boundary. If life arose on Earth shortly after surface water was available, life could have journeyed from Earth to another habitable world during this time, or vice versa if life had an early start in another planetary system. Credit: Amaya Moro-Martín.
Back in 2005, David Spergel (Princeton) and Fred Adams (University of Michigan) studied binary stars in young clusters. They found that the chances of life-bearing rocks being exchanged between star systems ranged from one in a million to one in a thousand, depending on the scenario invoked. Of the new work, Adams says:
“This paper takes the type of calculations that have been done before and makes an important generalization of previous work. Their work on chaos in this context also carries the subject forward. They make a careful assessment of a process that is dynamically quite complicated and chaotic in nature. They are breaking new ground from the viewpoint of dynamical astrophysics. Regarding the problem of lithopanspermia, this type of weak capture and weak escape is interesting because it allows for the ejection speeds to be small, and these slow speeds allow for higher probabilities of rock capture. To say it another way, chaos, in part, enhances the prospects for lithopanspermia.”
The paper is Belbruno et al., “Chaotic Exchange of Solid Material between Planetary Systems: Implications for Lithopanspermia,” published September 12 in Astrobiology (preprint). The Spergel and Adams paper is “Lithopanspermia in Star Forming Clusters,” Astrobiology Vol. 5, No. 4 (2005). Preprint available. This Princeton news release contains details about the simulations used in the Belbruno study.
The panspermia theory opens up some intersting questions, although I’m not clear how we could test that it happened.
If life formation is a very rare event, then we might expect living exoplanets to have very similar basic biology if seeded with alien life. OTOH, if life formation is easy, then even if life migrated between worlds, it might not be able to compete with endogenous life (or perhaps there will be a patchwork of successful and unsuccessful colonizations).
Supposing we find evidence of alien life that seems to match terrestrial biology in fundamental ways, does it imply common biology or convergent evolution of early biology?
And of course if panspermia is true, then life in the universe is common, so we are back to the Fermi question.
This would make it even more relevant to search for member stars of our sun’s birth cluster.
Are those traceable at all? And are any of them known in our galactic neighborhood?
can we infer what stars belonged to the same cluster as Sol did by backtracking star movements? or actually; how much back in time can we go with backtracking alone before the observational uncertainties make it unreliable?
It would be interesting to know this, because stars that belonged to that same cluster could have a higher probability of harboring planets with life
Ronald and lurscher…
That is a somewhat interesting idea. No doubt there have been too many disturbances in orbits since then (billions of years), but I do not know enough about it to be sure. It seems to me to be not just a computational issue, but one of not enough data about unpredictable phenomena (such as “rogue” planets or stars passing through).
Such “birth cluster” stars (if identifiable) might be good candidates for exoplanet research and even a bit of SETI examination. Our long-lost space cousins :)
All of this reminds me of the Mars rocks found that supposedly contains fossilized bacteria samples. Seems to me it is relatively cheap to continue checking things like this, both with Mars landers utilizing powerful microscopes as well as analyzing other meteorites that land on Earth or the Moon for similar traces.
Alpha Centauri has a very similar iron/hydrogen ratio to our Sun, it is therefore a very good indicator that they formed together
If panspermia does occur we could find proof in the A.C system
I don’t get the attraction to panspermia. If life arose elsewhere and then seeded the Earth, why not have it just start on the Earth? It’s the simplest answer.
There’s plenty of evidence that it indeed start here, no “vitam ex machina” (or “vitam ex spatio”) required.
If I remember correctly, the Solar System makes on the order of one galactic revolution every 200-250 million years, so that’s a dozen or more complete orbits since the time in question. By now, the sibling stars from the primordial cluster would be smeared all across the galaxy, I would think, perturbed over time onto separate paths by chaotic gravitational influences. If that’s true, it would indeed make it hard to put the (litho)panspermia hypothesis to the test.
@Alex Tolley: “And of course if panspermia is true, then life in the universe is common, so we are back to the Fermi question”.
Well, not quite, because this kind of lithopanspermia would only apply to member stars of the same birth cluster. So, if the arising of life (abiogenesis) is very rare indeed, then only the planets of the stars within the same birth cluster would have been seeded with life. Stars of other clusters would not have been seeded this way and, if life did not arise independently within a birth cluster itself, those clusters would remain sterile.
This bring up an old question: is there any possibility that extant life on Earth could have had its origin before the Late Heavy Bombardment. The sensible money would be on the “no” answer – but I loath the assumption that the most likely answer must be the correct one.
If current life has its origins before the LHB then it must have either been rooted in a community living several km underground at an ambient temperature around water’s boiling point or been the result of repeated reinfection by surface lithospheric communities that were wide-spread enough to be included in the “spall zones” of every major impact and could withstand all rigours associated with lithopanspermia.
A couple of thoughts in response to a few comments above…
This particular mechanism does only seem to apply to comparatively (in interstellar terms) short distances but see Wickramasinghe et al (2010) ‘Comets and the Origin of Life’ for a fuller discussion of possible panspermia mechanisms. Even this process would involve longer term diffusion as stars orbit around the galaxy.
Life beginning on earth would be the simpler solution – I would question that assumption if the evidence for a very early start to life on earth continues to mount. At the moment it is pretty certainly here by 3.5bya and possibly (probably?) by 3.8bya. That gives quite a narrow window after the LHB for pre-biotic evolution with even the simplest cells actually being very complex biochemically. Whilst I do think complexity theory has a contribution here it does seem to me simpler to suggest that, if micro-organisms can survive panspermia which the evidence suggests they probably can with some uncertainties, and the astrophysics suggests that organisms would be transferred (alive or dead), the simpler solution may be to move the pre-biotic and very early biological phases of evolution off earth to somewhere else to give it some time to actually happen.
This brings us back to the Fermi paradox….Well, yes…
I’ve always wondered why life arose on Earth only once. Perhaps life is just exceedingly rare and in fact arose in only one place.
It’s certainly the case that cell development is a complicated affair incompletely explained (as yet).
If the lithopanspermia hypothesis has any validity, we should still expect to find some sort of life in those traveling rocks. Presumably there must still be examples of those rocks in teh solar system. Can we determine which rocks are extra solar in origin and investigate those for life?
A panspermia theory for the origin of life on earth is unattractive for biologists as it means that the conditions are now potentially removed from Earth, i.e. that the primordial Earth might lack some feature necessary for life to start.
To Michael Spencer, are you certain life arose only once on Earth?
Convergent evolution only affects things that matter. There is also a lot of arbitrary characteristics of life that do not matter. Take the genetic code, for example. A multitude of different codes would have worked just the same, yet all life on Earth uses a single one. If we find excessive similarities in such things that do not matter functionally, we can conclude that two trees of life are related.
It sure would be the simpler solution. And I am highly sceptical of those early “microfossils”. I would definitely refrain from “pretty certainly” as a characterization of their reliability.
The earliest fossils we can find already shows signs of evolution from earlier forms. Unless they were planted there from elsewhere, this would indicate that life started on Earth much earlier, not longer after things literally cooled down. The early heavy celestial bombardments seem to have taken out these first natives of our planet and life had to start over again, no doubt more than once.
If nothing else this also shows that at least simple organisms can form in the early harsh stages of a planet’s formation and start up again as necessary.
I can’t lay my hands on the paper at the moment, but there have been studies of code optimality and our code is effictively optimal. Also don’t forget there are small variations. The code is not just a random mapping of codon triplets.
Iirc, these studies assume our biology, so it may be possible that other codes are optimal given a different biology, but possibly the optimality is universal assuming the bases and the amino acids available.
If you took most organisms on Earth right now (including many extremophiles) back to Earth post LHB, chances are slim that many would survive, since they didn’t evolve in that environment.
Yet, through some magic an organism that has been blasted from its home sweet home, traveled through space for millions of years, survived re-entry and lithobreaking on the Earth finds that environment just dandy.
The law of parsimony would through panspermia into jail.
Those claims that I have seen for the optimisation of the universal genetic code extend only so far as to which amino acids are placed in groups of similar code. They do not extend to ordering which residue has which code within a group, or as to which group of residue has which block of code, or even as to which of the three letters of the code should be most redundant.
You write “The earliest fossils we can find already shows signs of evolution from earlier forms. Unless they were planted there from elsewhere, this would indicate that life started on Earth much earlier, not longer after things literally cooled down. The early heavy celestial bombardments seem to have taken out these first natives of our planet and life had to start over again, no doubt more than once.”
And I am at a loss as to what evidence you are trying to reference.
Is it the alleged morphological sophistication of the first forms, the seemingly early (but much later than the first fossils) of cyanobacteria, or is it the disputed taxonomic branching evidence for a hyperthermic origin of LUCA???
Let’s assume life originated on earth. The earliest microbes would be adapted to that environment. We know that some would be ejected into space from large impacts and a small fraction of the biological material would reach other planets and some other star systems. What fraction would remain viable is less clear but some current microbes appear surprisingly tolerant of simulated space conditions or even some time in low earth orbit. Panspermia is likely to have occurred from earth to other locations. The chances of the earth being the first link in the chain, particularly given the complexity of micro-organisms, is low in my opinion.
We do need a definitive test or battery of tests, such as actually sending some bugs on a round trip or a sample return, but the indirect evidence is considerable already (see earlier ref)
What I should have concluded the earlier comment with, of course, was the observation that if biotic material can be said to be plausibly transferred between planets, but with uncertainty over viability, two conclusions can be drawn which might address the issue raised by Frank.
Firstly material would originate from a wide variety of different environments over time on each inhabited planet and from a variety of different worlds. This may address the question of having organisms capable of surviving on the early earth assuming some constraints on the range of planetary environments exist.
Secondly, even if we assume the biological material would all be dead by the time it arrived, Wesson (2010) pointed out the significant information content of such material which could help the probability of life arising.
The amount of data that has accumulated over the years supportive of panspermia is impressive and makes me think we really do need some decisive tests to finish this question off, one way or the other.
Anthony Mugan said on September 28, 2012 at 8:22:
“We do need a definitive test or battery of tests, such as actually sending some bugs on a round trip or a sample return, but the indirect evidence is considerable already (see earlier ref).”
There was an actual attempt put aboard the Russian Phobos-Grunt probe, which was supposed to return from the vicinity of Mars along with some surface samples of its largest moon, but we all know how far that mission got.
Hopefully there will be a chance to repeat this experiment, or perhaps perform an even more intricate one in the near future.
“I don’t get the attraction to panspermia. If life arose elsewhere and then seeded the Earth, why not have it just start on the Earth? It’s the simplest answer.”
It may seem that way but I believe that is because we are biased and we do not have all the information. It is also easier to study models suggesting life emerged on earth if you live on earth. But Occam’s Razor is a principle, not a law. Once it seemed simpler to say the sun revolved around the earth. The more we learn the more open the question should remain.
Regarding Fermi, life may be common but civilizations may be exceedingly rare. Who knows? Anyway, the Fermi question should have no relation to the evidence or models supporting panspermia.
I agree with Bob’s disagreement with FrankH over his “I don’t get the attraction to panspermia” comment, but disagree with Bob’s emphasis.
I think it reasonable that (given we can discount the old Steady State theory of cosmology) we may question the likelihood of panspermia in regard to the study of abiogenesis by using Occam’s Razor.
But when we look for life on other planets in our system, there is no reason to invoke an a priori belief that every instance of life there can only be via native origin. In fact, the default belief that life only originated once in our system would then be the indicated outcome of Occam’s razor if we knew life to be complex (we do) and mechanisms for life’s dispersal simple (we are current finding interesting practical and theoretical evidence in that regard).
Amazing Meteor Boomerangs Around Earth
By Kelly Beatty for Sky & Telescope
For the first time ever, a meteor has grazed in and out of Earth’s atmosphere, slowing enough to become a temporary satellite that lasted a full orbit.
By evening on September 21st, an earlier storm had moved eastward and left skies over the British Isles beautifully clear.
Martin Goff, an officer with the Greater Manchester [England] Police, was making his rounds when he spotted a dazzling meteor at 22:55 p.m. (21:55 Universal Time). “I immediately pulled the van over to better see the fireball,” he recounts. “Although not an experienced astronomical observer I was able to log relevant information such as altitude and azimuth relative to the straight road I was on and to trees and streetlights nearby.” He estimates it was about as bright as a full moon and remained visible for 35 to 40 seconds, fragmenting for at least the last half of that. “I was just flabbergasted to have seen it!”
He was hardly alone in his amazement. Friday-night crowds were out and about when the bolide appeared, delighting and amazing untold thousands as it broke into dozens of pieces as it glided east to east across the sky. Dirk Ross, who tracks bright meteors and meteorite finds worldwide, logged 564 eyewitness reports from England, Scotland, Ireland, France, Belgium, The Netherlands, and Norway.
A few hours later, Ross received another burst of 126 sightings. But these weren’t from Europe — instead, a fireball had appeared over southeastern Canada and the U.S. Northeast. What at first seemed the unlikely arrival of two dramatic bolides in a single night is now known to be something much more historic and scientifically profound.
Full article here:
Giant asteroid, mega-tsunami may have triggered Ice Age
Wednesday, 10 October 2012
by Rachael Bayliss
LONDON: A 2km-wide asteroid that hit Earth 2.5 million years ago may have triggered the Ice Age, according to a team of Australian researchers.
The monstrous Eltanin asteroid plunged into the Pacific Ocean 2.5 million years ago and generated a mega-tsunami with waves hundreds of feet high, wreaking devastation across the globe. It is the only identified deep-ocean impact in our planet’s history, and could prove to be as significant as the asteroid that wiped out the dinosaurs.
While previously little has been known about Eltanin and its subsequent impact on Earth, a team of Australian researchers has painstakingly gathered data from around the world to piece together the puzzle.
Full article here: