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#1280 by Dalhousie on 19 Dec, 2014 22:07
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It's so frustrating that they can't tell if it's the type of Methane that you would expect to see produced by biology as there just isn't enough of it being detected for Curiosity to analysis it.
It's important to remember that even if they could measure the isotope ratios, it wouldn't be definitive. Also, they will attempt to measure them if there is a big enough spike.
Isotope ratios are generally definitive of biogenic activity. Not in every case of course, but in most cases. -
#1281 by hop on 20 Dec, 2014 01:36
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Isotope ratios are generally definitive of biogenic activity. Not in every case of course, but in most cases.
On Earth, yes. On Mars... there are so many more unknowns it seems like a much harder case to make. It could be strongly suggestive (and super exciting) but calling it proof of life would be going out on a limb.
I've heard the MSL team asked about it a few times (including the recent press conference, ~43 minutes in) and every time they say they wouldn't consider it definitive. -
#1282 by Dalhousie on 20 Dec, 2014 20:42
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Isotope ratios are generally definitive of biogenic activity. Not in every case of course, but in most cases.
On Earth, yes. On Mars... there are so many more unknowns it seems like a much harder case to make. It could be strongly suggestive (and super exciting) but calling it proof of life would be going out on a limb.
I've heard the MSL team asked about it a few times (including the recent press conference, ~43 minutes in) and every time they say they wouldn't consider it definitive.
The MSL team are publically hedging their bets and being conservative. If they really thought that carbon isotopes aren't going to tell us anything, they wouldn't be measuring them, or sending such complex and finicy instruments as mass spectrometers.
As for the "Mars is different" bit, I disagree. The reason why biogenic processes almost always have a strong negative D13 value is because of basic thermodynamics. Mars does not have unique thermodynamics. We know that carbon isotopes systems behave the same as those on Earth from studies of organic and inorganic carbon in martian meteorites. -
#1283 by hop on 21 Dec, 2014 01:58
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If they really thought that carbon isotopes aren't going to tell us anything, they wouldn't be measuring them, or sending such complex and finicy instruments as mass spectrometers.
Errr.. not being definitive is not the same as telling us nothing, and there are plenty of good reasons to send fancy instruments and measure carbon isotopes even if you can't definitively answer that question.QuoteAs for the "Mars is different" bit, I disagree. The reason why biogenic processes almost always have a strong negative D13 value is because of basic thermodynamics.
One problem is knowing the ratio in whatever the methane was made from. Modern Mars atmospheric CO2 is almost certainly enriched with 13C due to atmospheric loss*. Can you tell the difference between biogenic methane produced from relatively modern atmosphere vs ancient aboigenic methane?
An extreme result with a high SNR could point very strongly one way or the other, but there's plenty of room for one that is only suggestive and fits both in the error bars.
* SAM puts the current value at +45, but there is disagreement with other measurements. See attached figure from http://www.sciencemag.org/content/341/6153/1238937
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#1284 by Dalhousie on 21 Dec, 2014 08:12
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If they really thought that carbon isotopes aren't going to tell us anything, they wouldn't be measuring them, or sending such complex and finicy instruments as mass spectrometers.
Errr.. not being definitive is not the same as telling us nothing, and there are plenty of good reasons to send fancy instruments and measure carbon isotopes even if you can't definitively answer that question.
And the biggest of those is being able to constrain formative processes of carbon bearing compounds.QuoteQuoteAs for the "Mars is different" bit, I disagree. The reason why biogenic processes almost always have a strong negative D13 value is because of basic thermodynamics.
One problem is knowing the ratio in whatever the methane was made from. Modern Mars atmospheric CO2 is almost certainly enriched with 13C due to atmospheric loss*. Can you tell the difference between biogenic methane produced from relatively modern atmosphere vs ancient aboigenic methane?
We would need enough methane or other organics to do it, but we should be able to.
Mars atmospheric C13 ratios seem to be variable, with values as depleted as -2.5 per million (Phoenix) to +45 to +46 (Curiosity), Viking measured +11 per mill and gas inclusions in Mars meteorites +15 per million. Terrestrial atmospheric carbon is somewhat lighter and has a smaller range about -4 to -12 per mill.
Inorganic carbon in Mars meteorites is in the range of +25 to +65 per mill, magmatic organic carbon is +16 per mill. Mantle carbon from Earth is -4 to -11. Edit: I am not sure where the light values the Leshin quotes come from. I will check the sources later today.
Terrestrial biogenic carbon is usually -16 to -50 (sometimes up to -80) per mill. So biogenic processes on Earth cause a shift of between 5 to 70 per mill. If this were to happen on Mars using the known inorganic reservoirs we can predict that some, though probably not all martian biogenic organic carbon (if it exists) will show values similar to terrestrial biogenic organic carbon, with values in the -10 to-40 range.
Interestingly, this is what we see. A recent paper by Lin et al. on the Tissint meteorite, which is probably the closest sample we have to martian regolith suggests that there is a population of martian organic compounds with values of -10 to -35 per mill, this is very similar toTissint is the closest sample we have to a martian regolith, these biogenic like signatures are almost certainly endogenous, sandwiched between two shock events and containing a deuterium enrichment similar to what we see for other martian materials and very different to terrestrial organics.
http://onlinelibrary.wiley.com/doi/10.1029/JB095iB09p14789/abstract
These values are also distinctive from almost all organic matter in carbonaceous chondrites, which are typically -10 to +40 per mill, with the exception of the insoluble organic component in some.
So while not conclusive (what is?) I think we can be confident that, should there be (or have been) biogenic processes on Mars, then it is possible for least some to show similar highly depleted DC13 values to terrestrial biogenic carbon. Certainly we see such values already in Tissint, so Curosity should be able to, if it can get enough organics. We can't rule out some unusual inorganic process, but it would have to be something very unusual and very different to anything we have seen before.
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#1285 by hop on 21 Dec, 2014 19:55
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We would need enough methane or other organics to do it, but we should be able to.
I would say we might be able to do it, depending on the the actual value of the result.QuoteMars atmospheric C13 ratios seem to be variable, with values as depleted as -2.5 per million (Phoenix) to +45 to +46 (Curiosity), Viking measured +11 per mill and gas inclusions in Mars meteorites +15 per million. Terrestrial atmospheric carbon is somewhat lighter and has a smaller range about -4 to -12 per mill.
(pedantic typo alert: per mil. = ‰ = per thousand.)
It's not clear how much of that variability is real. The Viking measurements had pretty large error bars.
SAM TLS and QMS results agree very well and should be very accurate, so if I was going to bet, I'd put my money on them, but the disagreement with Phoenix is puzzling. AFAIK that much regional or temporal variation wouldn't really be expected, but OTOH having a significant part of the atmosphere freeze and sublimate every year is outside our normal experience...
A couple of papers on atmosphere isotopes from 2013 discuss some of these issues:
http://www.sciencemag.org/content/341/6143/260
http://www.sciencemag.org/content/341/6143/263
(find full text may be found by googling the titles)
One open question from those is seasonal variation. I'd expect the MSL team to publish atmosphere results for a full Mars year (or more) at some point, but if they have I wasn't able to find it.QuoteSo while not conclusive (what is?) I think we can be confident that, should there be (or have been) biogenic processes on Mars, then it is possible for least some to show similar highly depleted DC13 values to terrestrial biogenic carbon.
I agree with this completely. The point I was trying to make is that the is a lot of room to be a good, high SNR measurement of the D13C in methane and still get an inconclusive result. You'd only have a strong case if the actual value fairly extreme.
On a different note, a recent, highly speculative paper published in Astrobiology suggests Curiosity may have already seen microbial mats:
http://online.liebertpub.com/doi/full/10.1089/ast.2014.1218
I wouldn't bet much on this one, but Noffke is an expert on these structures on Earth, not some random crank. -
#1286 by Moe Grills on 24 Dec, 2014 21:16
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Hop? Dalhousie? Both of you have ignored the NEED for a manned mission to Mars to settle these issues and return protected geo-samples and gas samples for definitive study back here on earth.
Yes there are issues of theoretical contamination on anything returned to earth from Mars.
But don't you think human beings are smart enough to have learned lessons from the ALH8001 controversy?
IMHO I think there was no contamination worth mentioning in those Martian meteorites, but that's another story. -
#1287 by Dalhousie on 25 Dec, 2014 23:37
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Sorry for the slow response, it’s been like Christmas here
We would need enough methane or other organics to do it, but we should be able to.
I would say we might be able to do it, depending on the actual value of the result.
I can live with thatQuoteQuoteMars atmospheric C13 ratios seem to be variable, with values as depleted as -2.5 per million (Phoenix) to +45 to +46 (Curiosity), Viking measured +11 per mill and gas inclusions in Mars meteorites +15 per million. Terrestrial atmospheric carbon is somewhat lighter and has a smaller range about -4 to -12 per mill.
(pedantic typo alert: per mil. = ‰ = per thousand.)
It's not clear how much of that variability is real. The Viking measurements had pretty large error bars.
That’s true, however the Viking values (with errors) overlap thoseof both multiple telescopic measurements and Phoenix. It’s the Curosity results that stand out. I have yet to see this properly discussed.QuoteSAM TLS and QMS results agree very well and should be very accurate, so if I was going to bet, I'd put my money on them, but the disagreement with Phoenix is puzzling. AFAIK that much regional or temporal variation wouldn't really be expected, but OTOH having a significant part of the atmosphere freeze and sublimate every year is outside our normal experience...
I agree, this is very strange.QuoteA couple of papers on atmosphere isotopes from 2013 discuss some of these issues:
http://www.sciencemag.org/content/341/6143/260
http://www.sciencemag.org/content/341/6143/263
(find full text may be found by googling the titles)
Thanks. I had already read those papers, however Mahaffy etal (2013) say they are similar to Viking when they are most clearly not. Webster etal (2013) recognises the differences, and (of course) says Curiosity is more accurate, based on gas inclusions in Mars meteorites. However the paper cite cites to support this is 30 years old. My library on gas inclusions in Mars meteorites is rather small, I will look into this in ten days when I can access my work library again. Bogard etal 92001) mentioned that the impact glass data shows a great range, but does not go into it.QuoteOne open question from those is seasonal variation. I'd expect the MSL team to publish atmosphere results for a full Mars year (or more) at some point, but if they have I wasn't able to find it.
The recent methane paper by Webster et al. covers a Martian year, but I don’t think any isotope measurements of the amosphere have been done with enough frequency to givean annual cycle.QuoteQuoteSo while not conclusive (what is?) I think we can be confident that, should there be (or have been) biogenic processes on Mars, then it is possible for least some to show similar highly depleted DC13 values to terrestrial biogenic carbon.
I agree with this completely. The point I was trying to make is that the is a lot of room to be a good, high SNR measurement of the D13C in methane and still get an inconclusive result. You'd only have a strong case if the actual value fairly extreme.
I agree
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#1288 by Dalhousie on 25 Dec, 2014 23:48
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I separated this comment out because it is a different issue.Quote
On a different note, a recent, highly speculative paper published in Astrobiology suggests Curiosity may have already seen microbial mats:
http://online.liebertpub.com/doi/full/10.1089/ast.2014.1218
I wouldn't bet much on this one, but Noffke is an expert on these structures on Earth, not some random crank.
Intriguing, isn’t it? I got the journal alert when this came out, Noffke’s work is of course familiar to me. It is certainly most interesting, and I can see what she drew the tentative suggestions she did.
The main problem I have is these are just general images, from two years ago, with no follow up at the time. They are now so far away that no follow up is possible. The best that can be hoped for is that any future suggestive features of this type will have more attention given to them.
Certainly there are at least two people on the Curiosity team who are very familiar with microbial features – John Grotzinger and Abby Allwood.
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#1289 by Dalhousie on 25 Dec, 2014 23:54
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Hop? Dalhousie? Both of you have ignored the NEED for a manned mission to Mars to settle these issues and return protected geo-samples and gas samples for definitive study back here on earth.
Yes there are issues of theoretical contamination on anything returned to earth from Mars.
But don't you think human beings are smart enough to have learned lessons from the ALH8001 controversy?
IMHO I think there was no contamination worth mentioning in those Martian meteorites, but that's another story.
You are right of course. I am a strong advocate of crewed missions. But we have to work with the data we have, not what we would like. And this is a Curiosity thread after all
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But even with returned samples there may well be debate. Even now, some people still refuse to admit that the 3.4 Ga stromatolites in the Pilbara are biogenic, despite more than 40 years of work on them! -
#1290 by Bob Shaw on 26 Dec, 2014 00:01
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Hop? Dalhousie? Both of you have ignored the NEED for a manned mission to Mars to settle these issues and return protected geo-samples and gas samples for definitive study back here on earth.
Yes there are issues of theoretical contamination on anything returned to earth from Mars.
But don't you think human beings are smart enough to have learned lessons from the ALH8001 controversy?
IMHO I think there was no contamination worth mentioning in those Martian meteorites, but that's another story.
Back contamination to Earth really isn't that likely; FORWARD contamination which obscures/destroys or even eats Martian relict or perhaps current biology is far more of a problem. Truth to tell, we may already be too late, between meteorites and early spacecraft. Life on Mars may actually be evidence of life on Earth. -
#1291 by Dalhousie on 26 Dec, 2014 00:50
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Hop? Dalhousie? Both of you have ignored the NEED for a manned mission to Mars to settle these issues and return protected geo-samples and gas samples for definitive study back here on earth.
Yes there are issues of theoretical contamination on anything returned to earth from Mars.
But don't you think human beings are smart enough to have learned lessons from the ALH8001 controversy?
IMHO I think there was no contamination worth mentioning in those Martian meteorites, but that's another story.
Back contamination to Earth really isn't that likely; FORWARD contamination which obscures/destroys or even eats Martian relict or perhaps current biology is far more of a problem. Truth to tell, we may already be too late, between meteorites and early spacecraft. Life on Mars may actually be evidence of life on Earth.
We have yet to find any part of Mars where terrestrial life can thrive. There are some potential areas but we haven't landed there yet.
http://online.liebertpub.com/doi/abs/10.1089/ast.2014.1227 -
#1292 by Bob Shaw on 26 Dec, 2014 00:58
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Oh, certainly! But, at the point where life is (perhaps) found you may be sure that the long knives will be out for it, with forward contamination as the chief accusation. See also Lake Vostok...
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#1293 by Dalhousie on 26 Dec, 2014 01:04
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Oh, certainly! But, at the point where life is (perhaps) found you may be sure that the long knives will be out for it, with forward contamination as the chief accusation. See also Lake Vostok...
It depends on it's biochemistry. if it has a different chemical basis then it can't be contamination.
If it is DNA based then the degree of similarity with terrestrial organisms should tell whether or not it is from here and how long ago.
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#1294 by hop on 26 Dec, 2014 18:48
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The main problem I have is these are just general images, from two years ago, with no follow up at the time. They are now so far away that no follow up is possible. The best that can be hoped for is that any future suggestive features of this type will have more attention given to them.
Yeah, hard to see it going beyond an intriguing possibility unless they find a similar features again.
There was reportedly serious discussion in the team whether they should just spend the whole primary mission in Glenelg.
There's an interview with Noffke about this paper at http://wowsignal.libsyn.com/burst-3-miss-on-marsQuoteCertainly there are at least two people on the Curiosity team who are very familiar with microbial features – John Grotzinger and Abby Allwood.
Dawn Sumner is another: http://mygeologypage.ucdavis.edu/sumner/Home.html -
#1295 by Dalhousie on 26 Dec, 2014 21:37
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The main problem I have is these are just general images, from two years ago, with no follow up at the time. They are now so far away that no follow up is possible. The best that can be hoped for is that any future suggestive features of this type will have more attention given to them.
Yeah, hard to see it going beyond an intriguing possibility unless they find a similar features again.
One can be hopeful. Microbial mats are very common in terrestrial sediments, even the oldest. one would prefer stromatolites of course, as they are even more distinctive.QuoteThere was reportedly serious discussion in the team whether they should just spend the whole primary mission in Glenelg.
Interesting, I wonder whether there were early indications to wheel damage influencing this decision? Glenelg was interesting, but not that interesting, IMHO, enough to cancel going to Mt Sharp.QuoteThere's an interview with Noffke about this paper at http://wowsignal.libsyn.com/burst-3-miss-on-mars
Thanks, it is always interesting to hear what people sound like, not matter how much of their stuff you have read. She says that the Glenelg features are not easy to see, which is fair enough.QuoteQuoteCertainly there are at least two people on the Curiosity team who are very familiar with microbial features – John Grotzinger and Abby Allwood.
Dawn Sumner is another: http://mygeologypage.ucdavis.edu/sumner/Home.html
I am less familiar with her work but she is indeed.
Attached is a modern mat I photographed near Israelite Bay WA
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#1296 by hop on 26 Dec, 2014 22:18
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Interesting, I wonder whether there were early indications to wheel damage influencing this decision?
I'm going from memory, and may have given the wrong impression. IIRC in one of the press conferences Grotzinger said something along the lines of how they had found a habitable environment clays, etc. which was the primary goal, so they asked the team if they should dig in there rather than going to Mt Sharp, but the consensus was to go.
So "seriously" as in it was a real option, not necessarily that it was a close decision.
My feeling is the severity of the wheel issue wasn't apparent until they were on the way, although it's hard to be certain since there was a long time between when they started worrying and when they acknowledged it publicly. -
#1297 by Dalhousie on 26 Dec, 2014 22:25
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Interesting, I wonder whether there were early indications to wheel damage influencing this decision?
I'm going from memory, and may have given the wrong impression. IIRC in one of the press conferences Grotzinger said something along the lines of how they had found a habitable environment clays, etc. which was the primary goal, so they asked the team if they should dig in there rather than going to Mt Sharp, but the consensus was to go.
So "seriously" as in it was a real option, not necessarily that it was a close decision.
My feeling is the severity of the wheel issue wasn't apparent until they were on the way, although it's hard to be certain since there was a long time between when they started worrying and when they acknowledged it publicly.
That makes sense. They had travelled less than a km then, the wheel problem didn't show up until they had done a kilometre or so more.
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#1298 by Bob Shaw on 26 Dec, 2014 23:27
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Oh, certainly! But, at the point where life is (perhaps) found you may be sure that the long knives will be out for it, with forward contamination as the chief accusation. See also Lake Vostok...
It depends on it's biochemistry. if it has a different chemical basis then it can't be contamination.
If it is DNA based then the degree of similarity with terrestrial organisms should tell whether or not it is from here and how long ago.
Oh, true in both cases. But...
If the chemical basis is the same, it *can* be contamination, but still might not be, inasmuch as life chemistry might well reinvent the wheel in all sorts of places. Ideally, we really want some nice, well-adapted RNA organisms or their traces, even if the DNA guys ate them later - not a wholly unlikely outcome, either! Would fossil metabolites of RNA organisms demonstrate different chirality to DNA critters (eg perhaps none at all), and would these perhaps be detectable? That would be a serious result if discovered! It might even be worth looking at Pre-Cambrian rocks on Earth (and, as I've oft repeated, on the Moon when we eventually start to strip mine it).
If it is DNA based, then the best we can hope for is the date of a last common ancestor, and as crust material flows back and forth across the Inner Solar System then that might not help.
As for forward contamination, the Soviet landers (yes, plural - just because we only have an idea of what happened to one of them doesn't mean at least one of the others didn't land, even if in (ahem) a disassembled condition) and parachutes don't appear to have been sterilised; efforts were made with Viking, but not so much with subsequent US landers, deliberate or not. In some respects, a visit to the Mars-3 site by a nice, sterile sample-return vehicle might be seriously interesting, and might even prove that there is life on Earth, and even (briefly) on Mars...
Finally:
We do already have an example of a life-bearing object suffering a meteoric-like entry into a planetary atmosphere, and the inhabitants of said object not only surviving, but breeding: the famous Columbia worms. OK, we're not talking about lengthy exposure to space conditions, but we've already seen the unexpected survival of reasonably advanced organisms, which might make it even more likely that tougher varmints could do their thing!
Just sayin'... -
#1299 by Bob Shaw on 30 Dec, 2014 01:15
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I've downloaded and read the paper: Ancient Sedimentary Structures in the < 3.7 Ga Gillespie Lake Member, Mars, That Resemble Macroscopic Morphology, Spatial Associations, and Temporal Succession in Terrestrial Microbialites and it's certainly persuasive. I never expected to see morphological, rather than chemical, evidence of past Martian life, however! She's almost suggesting something as grossly physical as stromatolites, rather than strangely differentiated layers. My gut feeling is that the jury is out, but if another, similar, formation is found then Nora Noffke's stimulating interpretation will be well on the way to vindication. As ever, the key with such matters is as much prediction as interpretation: when you turn the corner are the structures as predicted, or was your prediction lacking?
Needless to say, I'd be delighted if evidence of more microbial mats are found!
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