Order of Kilopi
From SpaceDaily:
The watery environment of early comets, together with the vast quantity of organics already discovered in comets, would have provided ideal conditions for primitive bacteria to grow and multiply. So argue Professor Chandra Wickramasinghe and his colleagues at the Cardiff Centre for Astrobiology in a paper published in the International Journal of Astrobiology.
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It is possible that water was first delivered to the Earth by a comet hitting the Earth in its development process. Also a good book to read about this would be Comet by Carl Sagan and Ann Druyan.
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I'm surprised he's hit on comets as possible mini habitable worlds. There's lots of evidence that certain main belt asteroids have had liquid water and formed complex biology-related organics in the deep past. Going by this story on universe today it seems probable that many still contain ice dating back from that time. By contrast IIRC material gathered from comets seems comparitively primitive, a window onto an even earlier solar system (which is fascinating in itself).
That small, ancient worlds, with liquid water existed seems likely, and it's possible that some may have got as far as primitive life before they froze, but I would put my money on the asteroid belt being the place to look. Of course going by the story I linked above there seems to be some blurring between comets and asteroids so we can both be right...
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Having read the abstract I'm both for and against: He mentions carbanaceous chondrites as evidence for liquid water in some small bodies, and there does seem to be crossover between comets and asteroids, thats fine. But then he starts talking about the comets being seeded by bacteria from the presolar nebula, and last time I checked interstellar panspermia was, umm not supported by either numbers or evidence, to put it politely.
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Why focus on comets/asteroids that may have had liquid water (though the article didn't really mention liquid water, just 'water' which must be water-ice) for the origin of life, when there are far more stable and hospitable incubators - planets! And even if, during the formation of the solar system, there were planetesimals with liquid water, they would have existed in that state only fleetingly, with no protection from the solar wind, no atmosphere, and no magnetic field. As sources of raw materials, yes, absolutely, but far and away the most likely point of origin are planetary bodies.Originally Posted by marsbug
Order of Kilopi
Professor Chandra Wickramasinghe has been arguing for this possibility for years. He isn't any closer to proving it than he was years ago.
http://en.wikipedia.org/wiki/Chandra_Wickramasinghe
Note that he also thinks that SARS may be of extraterrestrial origin; a hypothesis which seems to have very little support in the mainstream.
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I have to pull you up on that, there were a lot more radioisotopes around near the solar systems beginning to power internal heating and vulcansim, recently meteorite evidence has suggested that early, warm, planetesimals generated their own magnetic fields, had distinct crusts and mantals (were differentiated), and could have sustained internal oceans for hundred of thousands to millions of years, in the case of the largest concievably even billions of years.
That seems a promising environment for life to start, especially as its thought it began quite quickly on earth. Thats not the same as saying life on earth started there, just that it could have started there as well as here. Lots of meteorites and asteroids are believed to be fragments from much larger bodies (Eg Ceres or Vesta), so if life started on those bodies way back when they had liquid they may carry evidence of it. And unless I had something crazy in my eye wasn't the article in the OP specifically about evidence for liquid water in comets?I'm not convinced thats right myself but I'm sure thats what it says.
Last edited by marsbug; 2009-Aug-06 at 08:24 PM.
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Thanks marsbug, I was unaware of the latest evidence regarding the formation of magnetic fields in planetesimals. At the same time, I had it in mind that I was in the "Life on Earth Came From Other Planets" thread (it's hard to keep track of a.dim's panspermic threads sometimes!), so within the context of this thread I agree with you when you said:
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No worries, a lot of threads follow similar themes, and I get them mixed up too more often than not!
Order of Kilopi
As do I!
Interesting how all these "panspermic" threads are the direct result of science news and research. It seems Astrobiology is where it's at!
Order of Kilopi
Yes, it states a large fraction of comets in our solar system did indeed have liquid interiors in the past.
Is it plausible, that comets et al, are fragments of much larger bodies - planets? - which were blown out by the supernova event which is thought to have played a part in the formation of our solar system?
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As do I!
Interesting how all these "panspermic" threads are the direct result of science news and research. It seems Astrobiology is where it's at!
It sure is! Until life elsewhere is actualy discovered. Then it'll be old hat.
I wonder what the disputes on the "frontiers" will be then.
Order of Kilopi
I can think of some possible areas of dispute. I'd like to see what A.DIM says if life is found on, say, Mars, but it's found to be very different from Earth life, strongly arguing against common origin.
I say there is an invisible elf in my backyard. How do you prove that I am wrong?
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It would be a wrinkle. But I don't think it would be a major kink. If Mars, Europa and Enceledus all had unique life that would be a major kink. But it would also be major interesting. Particularly how it would reflect on the probabilities of life elsewhere.
Order of Kilopi
Really? It would be a powerful argument against panspermia and for local abiogenesis. I think it would be a huge deal. But then, there's part of the dispute right there. I doubt A.DIM would give up on panspermia easily.
Oh, sure, it would be very interesting, but it wouldn't be panspermia.If Mars, Europa and Enceledus all had unique life that would be a major kink. But it would also be major interesting. Particularly how it would reflect on the probabilities of life elsewhere.
I say there is an invisible elf in my backyard. How do you prove that I am wrong?
The Leif Ericson Cruiser
Order of Kilopi
No.
I say there is an invisible elf in my backyard. How do you prove that I am wrong?
The Leif Ericson Cruiser
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As plausible as the exploding planet being called Krypton...
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I guess I could put it like this.
If Europan life was shown to be related to us by mitochodrial DNA then the question would be how long ago does the stage of DNA mutation show the branch from us occured. If it occured before the solar system formed then it would confirm extra solar panspermia. If it occured after then it would confirm extraterrestrial panspermia. It would be probable intrasolar panspermia but it would not rule out extrasolar panspermia.
If it is not related to us it would be silent on extraterrestrial, extraeuropan and extra solar panspermia. It would only confirm that it is not Earth-Europan panspermia. It would not rule out panspermia. Just as life on Earth does not A-Priori rule out extraterrestrial panspermia.
It would be just one data point of two for the probability calculation of the likelyhood for local abiogenesis. The more data points of this kind the more probable is local abiogenesis. Still only a probability not a confirmation. Confirmation requires different evidence.
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I had proposed pretty much the same idea in one of my past threads. It makes sense? If the earth had water but no bacteria to reproduce beforehand. It seems to me the only difference between life and a rock is that life consumes energy and a rock doesnt? The bacteria could have led to fermentation of sugars etc..?
Last edited by coliver; 2009-Aug-12 at 09:39 AM.
Order of Kilopi
Nobody said it would rule it out. However, it would be a strong argument against it, and would be a strong argument for local abiogenesis.
Which would double the number of available data points.It would be just one data point of two for the probability calculation of the likelyhood for local abiogenesis.
I say there is an invisible elf in my backyard. How do you prove that I am wrong?
The Leif Ericson Cruiser
Banned
If we found a billion planets with life that was not related to us or each other and there was only one that was related to another it would confrirm panspermia. If that one was related to us it would confirm extraterrestrial panspermia. If the mutation stage showed that the split occured before the solar system formed... etc see above. It's no longer a question with only a probability solution no matter how many data points you have. Agreed?
Assuming our understanding of mitochondrial DNA mutation is correct. But that's another topic.
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What's there to agree with? A litany of extremely hypothetical scenarios building a house of cards argument for panspermia?
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I would have thought, far from confirming panspermia, such an observation would confirm the possibility of rather rare interplanetary transfers of life - which I had assumed to be a different thing from panspermia.
I would not, for instance, regard the idea that our biosphere started on Mars (interesting, but who knows?) as panspermia.
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Technically, you're right. We have been using the term "panspermia" as "interplanetary transfers of life".
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Yes. I notice that the Wikipedia article remarks: Because the term "panspermia" is more well-known, it tends to be used in reference to what should strictly speaking be called "exogenesis".
Oh well, my philosophical turn of mind - deeply unpopular in parts of this board - prefers tighter definitions.
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Just in passing: it seems that comets probably contain at least two types of amine and one amino acid (this paper)however over a hundred amino acids have been detected in carbanceous chondrite meteorites (this paper), which also show much evidence of being altered by liquid water on their parent bodies (eg here, here and here and here....). I think the evidence at the moment speaks for itself as to where the most habitable parts of the ancient solar system were. Although comets are as yet much less well understood than CC meteorites for obvious reasons!
Edit: Going by the wikipedia definition:you could easily argue that the existence of the basic chemistry of life on bodies like comets proves panspermia. These bodies do indeed transport and deposit the 'seeds of life' across the solar system.Panspermia (Greek: πανσπερμία from πᾶς/πᾶν (pas/pan) "all") and σπέρμα (sperma) "seed") is the hypothesis that "seeds" of life exist already all over the Universe, that life on Earth may have originated through these "seeds", and that they may deliver or have delivered life to other habitable bodies
Last edited by marsbug; 2009-Aug-14 at 11:28 AM.
Order of Kilopi
Indeed it would.
I daresay it's in our near future to know whether or not this is the case.
At that point I might argue planets, stars, even galaxies, are closed systems with the potential for abiogenesis. Life everywhere but not related.
Order of Kilopi
Why not?
Please explain.
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Comets are leftover material from when the solar system was created. So I don't think that they are pieces from a long lost planet. Plus there are over a trillion comets in the Oort Cloud. Also it is believed that comets were formed in the vicinity of Uranus and Neptune. Because the outer solar system is not the place for terrestrial formation, the chances of comets coming from rocky planets are not plausible.
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What about comets coming from collisions with/destructions of "Plutoids" or "Europoids"?
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