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TL/DR: A paper reports (appropriately conservatively) on tantalizing evidence from Gale crater. Curiosity's SAM lab heated 24 powdered rock samples to 850 °C, r

TL/DR: A paper reports (appropriately conservatively) on tantalizing evidence from Gale crater. Curiosity's SAM lab heated 24 powdered rock samples to 850 °C, releasing their solid carbon as methane gas. The onboard Tunable Laser Spectrometer then measured the carbon isotopes in that gas and found more 12C than would be expected based on the 12C to 13C ratio in the modern Martian atmosphere. On Earth, life preferentially uses 12C over the heavier 13C, bioaccumulating it, so we observe significantly more 12C than 13C in ancient rocks where life grew. Did ancient Martian microbial methanogenesis concentrate this isotope at Gale crater as it built up complex organic molecules? Maybe. Two other hypotheses offer abiotic explanations: one suggests that UV light could have caused CO2 in the Martian atmosphere to form isotopically enriched carbon monoxide molecules that settled to the surface, the other wonders if the isotopes arrived from space when our solar system drifted through a 13C-depleted giant molecular cloud hundreds of millions of years ago. “On Earth, processes that would produce the carbon signal we’re detecting on Mars are biological,”[1] but we don’t understand the Martian carbon cycle well enough yet to have any real confidence. As with all tantalizing results about microbial extraterrestrial life so far, this will probably turn out to be due to a physicochemical process we don’t yet understand. Or maybe not. I'll be covering this more in the next issue of Orbital Index (https://orbitalindex.com/ https://orbitalindex.com/). [1] https://www.nasa.gov/feature/goddard/2022/nasa-s-curiosity-rover-measures-intriguing-carbon-signature-on-mars/ https://www.nasa.gov/feature/goddard/2022/nasa-s-curiosity-r...

thatcherc 5y ago
> On Earth, life preferentially uses 12C over the heavier 13C, bioaccumulating it, so we observe significantly more 12C than 13C in ancient rocks where life grew. If (like me) you're wondering why life prefers to use carbon-12 over carbon-13, it appears to be because carbon-12 is simple lighter and thus more likely to diffuse into an organism: From [1]: Due to differential uptake in plants as well as marine carbonates of 13C, it is possible to use these isotopic signatures in earth science. Biological processes preferentially take up the lower mass isotope through kinetic fractionation. NOAA has a bit more detail on the diffusion of carbon isotopes into organism [2]. [1] - https://en.wikipedia.org/wiki/Carbon-13#Uses_in_science https://en.wikipedia.org/wiki/Carbon-13#Uses_in_science [2] - https://gml.noaa.gov/outreach/isotopes/stable.html https://gml.noaa.gov/outreach/isotopes/stable.html
- nousermane 5y ago
  From [1] above: > atmospheric, [marine] carbonate, and plant derived δ13C values all differ. So, there is a mineral process that can explain change in isotope ratio, which requires water. And also a biological process with the same outcome, also requiring water. In other words, this looks like a solid new piece of evidence in support of presence of liquid water on Mars in the past. Evidence of life though? That is less certain.
mrfusion 5y ago
Is heating rocks a method of producing methane on Mars? How does that work?
petschge 5y ago
Note that the atmosphere is more likely to loose 12C over time than 13C. (It's the lighter molecule and will have larger speeds at equal temperatures, making Jeans escape more likely). The paper itself says "the δ13C composition of the atmosphere may have been less 13C enriched when Gale crater sediments were deposited" (compared to now). I am not sure how they exclude that as an explanation why deposits are more 12C rich then the atmosphere is now.
- tectonic 5y ago
  That's a really interesting point. I'd like to know the answer.
julienchastang 5y ago
> but we don’t understand the Martian carbon cycle well enough yet to have any real confidence. As with all tantalizing results about microbial extraterrestrial life so far, this will probably turn out to be due to a physicochemical process we don’t yet understand. Or maybe not. That's right. I think NASA has learned its lessons from the original Viking missions that initially offered tantalizing evidence of biological chemistry only to turn out that there are non-biological explanations for the data. The lesson there is you have to understand the inorganic chemistry of Martian geology before going further in the search for biosignatures.
areoform 5y ago
To add to Tectonic's amazing comment. There's another reason why this is an extremely important find. The 12C concentration exists in a gradient. I can't say who this person is, but they're a senior scientist involved with the project. They pointed out something profound based on the history of the crater. water came over the rim of the crater and it slowly evaporated, down to the bottom, until it evaporated completely. If there was life there, then it followed this water all the way down, before its eventual death (?) due to dehydration. And the signatures match that hypothesis! The most anomalous signatures are the ones from the samples taken at the bottom of the crater. What's even more exciting is that the other two phenomena that are used as examples would have left a wider distribution. The specific pattern in which the signatures were found are even more suggestive of life, but all other hypotheses need to be eliminated first. - If it is indeed life, this changes everything. I have been in favor of orbitals for space settlement for a long time, and this reinforces my beliefs. We might have to declare Mars to be the solar system's largest natural preserve and outlaw human settlement (other than Mars bases for research into this life). We will carry our microbiome to Mars, and any large scale settlement will have inevitable leakage of our microbiome to the subsurface layers of Mars, causing the microbes we have to out-compete (and perhaps mingle?) the life that exists on Mars. (if it exists) At the very least, making a settlement on Mars should be put on hold until we have had a definitive detection and have found the native Martians. This is one of the most important scientific finds in human history.
- d883kd8 5y ago
  Why do you assume Earth microbes would outcompete martian microbes in their native environment?
  - AnimalMuppet 5y ago
    Yeah. More, why do you assume that martian microbes would not kill us? We don't just need quarantine to protect life on Mars. We need quarantine to protect life on Earth. (Presuming that this actually is life, which, despite the tantalizing hints, is still a presumption...)

thatcherc 5y ago

> On Earth, life preferentially uses 12C over the heavier 13C, bioaccumulating it, so we observe significantly more 12C than 13C in ancient rocks where life grew. If (like me) you're wondering why life prefers to use carbon-12 over carbon-13, it appears to be because carbon-12 is simple lighter and thus more likely to diffuse into an organism: From [1]: Due to differential uptake in plants as well as marine carbonates of 13C, it is possible to use these isotopic signatures in earth science. Biological processes preferentially take up the lower mass isotope through kinetic fractionation. NOAA has a bit more detail on the diffusion of carbon isotopes into organism [2]. [1] - https://en.wikipedia.org/wiki/Carbon-13#Uses_in_science https://en.wikipedia.org/wiki/Carbon-13#Uses_in_science [2] - https://gml.noaa.gov/outreach/isotopes/stable.html https://gml.noaa.gov/outreach/isotopes/stable.html

nousermane 5y ago
From [1] above: > atmospheric, [marine] carbonate, and plant derived δ13C values all differ. So, there is a mineral process that can explain change in isotope ratio, which requires water. And also a biological process with the same outcome, also requiring water. In other words, this looks like a solid new piece of evidence in support of presence of liquid water on Mars in the past. Evidence of life though? That is less certain.

mrfusion 5y ago

Is heating rocks a method of producing methane on Mars? How does that work?

petschge 5y ago

Note that the atmosphere is more likely to loose 12C over time than 13C. (It's the lighter molecule and will have larger speeds at equal temperatures, making Jeans escape more likely). The paper itself says "the δ13C composition of the atmosphere may have been less 13C enriched when Gale crater sediments were deposited" (compared to now). I am not sure how they exclude that as an explanation why deposits are more 12C rich then the atmosphere is now.

tectonic 5y ago
That's a really interesting point. I'd like to know the answer.

julienchastang 5y ago

> but we don’t understand the Martian carbon cycle well enough yet to have any real confidence. As with all tantalizing results about microbial extraterrestrial life so far, this will probably turn out to be due to a physicochemical process we don’t yet understand. Or maybe not. That's right. I think NASA has learned its lessons from the original Viking missions that initially offered tantalizing evidence of biological chemistry only to turn out that there are non-biological explanations for the data. The lesson there is you have to understand the inorganic chemistry of Martian geology before going further in the search for biosignatures.

areoform 5y ago

To add to Tectonic's amazing comment. There's another reason why this is an extremely important find. The 12C concentration exists in a gradient. I can't say who this person is, but they're a senior scientist involved with the project. They pointed out something profound based on the history of the crater. water came over the rim of the crater and it slowly evaporated, down to the bottom, until it evaporated completely. If there was life there, then it followed this water all the way down, before its eventual death (?) due to dehydration. And the signatures match that hypothesis! The most anomalous signatures are the ones from the samples taken at the bottom of the crater. What's even more exciting is that the other two phenomena that are used as examples would have left a wider distribution. The specific pattern in which the signatures were found are even more suggestive of life, but all other hypotheses need to be eliminated first. - If it is indeed life, this changes everything. I have been in favor of orbitals for space settlement for a long time, and this reinforces my beliefs. We might have to declare Mars to be the solar system's largest natural preserve and outlaw human settlement (other than Mars bases for research into this life). We will carry our microbiome to Mars, and any large scale settlement will have inevitable leakage of our microbiome to the subsurface layers of Mars, causing the microbes we have to out-compete (and perhaps mingle?) the life that exists on Mars. (if it exists) At the very least, making a settlement on Mars should be put on hold until we have had a definitive detection and have found the native Martians. This is one of the most important scientific finds in human history.

d883kd8 5y ago
Why do you assume Earth microbes would outcompete martian microbes in their native environment?
- AnimalMuppet 5y ago
  Yeah. More, why do you assume that martian microbes would not kill us? We don't just need quarantine to protect life on Mars. We need quarantine to protect life on Earth. (Presuming that this actually is life, which, despite the tantalizing hints, is still a presumption...)