3 ms·

I am not a biologist. I could be entirely wrong in which case please educate me. :) My understanding was that life would be "detected" by finding chemical si

by loxias 4y ago

I am not a biologist. I could be entirely wrong in which case please educate me. :) My understanding was that life would be "detected" by finding chemical signatures in the atmosphere which could not exist at a "steady state" without biological creatures there doing things. Is this what you mean by telltale signatures? (A++ username)

adastra22 4y ago
Yes, astrobiologists distinguish between direct detection of life and biosignatures. The latter are things for which we don’t have non-biological explanations at this time, but which we don’t consider adequate evidence by themselves for life. FWIW we’ve already detected bio signatures for life in the atmosphere of Mars (seasonal methane emissions). And maybe Venus, though that is less clear. (Thanks!)
- loxias 4y ago
  Thanks for this, your phrasing makes the concept more clear. Can you give a (fictitious as necessary) example of what would constitute "direct detection of life", from an astrobiological perspective? Given our window to the universe is through telescopes I'm having difficulty imagining/distinguishing how to draw the line between "observed data for which we don't have any non-biological explanation" and something even stronger. Like, does "direct detection of life" only include "we sent something there and found life"? > we’ve already detected bio signatures for life in the atmosphere of Mars (seasonal methane emissions). And ~Europa~ Enceladus too, right? ~ISTR seeing some paper about plumes of water vapor, as well as chemistry for which we don't have any non-biological explanation.~ I found it -- I was thinking of in 2017 when H2, CO2 and CH4 were detected at a ratio in thermodynamic disequilibrium . Edit: I'm guessing "direct detection" in an astrobiological context would be something that builds on "direct detection" in an exoplanet context, a concept I already understand a bit -- friend of mine wrote her thesis on direct detection and imaging of exoplanets 15 years ago. :)
  - TheOtherHobbes 4y ago
    https://astrobiology.nasa.gov/research/life-detection/ladder/ https://astrobiology.nasa.gov/research/life-detection/ladder...
    - loxias 4y ago
      Yeah. I found and read that before my above comment (and skimmed some of the associated paper[1]) but all that says is direct detection hasn't been attempted since Viking, and that most good signals require in situ or sample return. It still doesn't answer my question! "astrobiologists distinguish between direct detection of life and biosignatures". The highest methods in terms of strength of evidence obtainable with remote sensing would be finding "deviations from thermodynamic equilibrium and/or kinetics" of "co-located reductant and oxidant" or "element or isotope fractionations indicative of metabolism". Which sound a whole lot like a detection of a biosignature, which "astrobiologists distinguish" from direct detection . :) I suspect direct detection in an astrobiological context must mean either "direct, as in we physically touched it" or maybe "a signature found using direct imaging". Definitions are hard. :) 1: https://www.liebertpub.com/doi/full/10.1089/ast.2017.1773 https://www.liebertpub.com/doi/full/10.1089/ast.2017.1773
      - adastra22 4y ago
        Direct observation means, well, observing it directly. Seeing living cells in a microscope. Growing it in a Petri dish. Genetic testing, if it turns out it has DNA or RNA like us. Within our own solar system that generally means sample return, or sending people with a full biology lab. For an extrasolar planet? I don't think the astrobiology community is of a single mind regarding what should count as direct observation there. We're not sending people or doing sample return for thousands of years. One common opinion I've heard is that seeing an atmospheric spectrograph indicating the presence of biomarkers like oxygen and methane within the habitable zone would be a bio signature, but multi pixel imaging of the planet would be required to claim direct observation. I'm not sure this is a very strong scientific distinction, however. I'm not an astrobiologist btw, but I used to work at astrobiology.nasa.gov. Small world!

by loxias 4y ago

adastra22 4y ago

Yes, astrobiologists distinguish between direct detection of life and biosignatures. The latter are things for which we don’t have non-biological explanations at this time, but which we don’t consider adequate evidence by themselves for life. FWIW we’ve already detected bio signatures for life in the atmosphere of Mars (seasonal methane emissions). And maybe Venus, though that is less clear. (Thanks!)

loxias 4y ago
Thanks for this, your phrasing makes the concept more clear. Can you give a (fictitious as necessary) example of what would constitute "direct detection of life", from an astrobiological perspective? Given our window to the universe is through telescopes I'm having difficulty imagining/distinguishing how to draw the line between "observed data for which we don't have any non-biological explanation" and something even stronger. Like, does "direct detection of life" only include "we sent something there and found life"? > we’ve already detected bio signatures for life in the atmosphere of Mars (seasonal methane emissions). And ~Europa~ Enceladus too, right? ~ISTR seeing some paper about plumes of water vapor, as well as chemistry for which we don't have any non-biological explanation.~ I found it -- I was thinking of in 2017 when H2, CO2 and CH4 were detected at a ratio in thermodynamic disequilibrium . Edit: I'm guessing "direct detection" in an astrobiological context would be something that builds on "direct detection" in an exoplanet context, a concept I already understand a bit -- friend of mine wrote her thesis on direct detection and imaging of exoplanets 15 years ago. :)
- TheOtherHobbes 4y ago
  https://astrobiology.nasa.gov/research/life-detection/ladder/ https://astrobiology.nasa.gov/research/life-detection/ladder...
  - loxias 4y ago
    Yeah. I found and read that before my above comment (and skimmed some of the associated paper[1]) but all that says is direct detection hasn't been attempted since Viking, and that most good signals require in situ or sample return. It still doesn't answer my question! "astrobiologists distinguish between direct detection of life and biosignatures". The highest methods in terms of strength of evidence obtainable with remote sensing would be finding "deviations from thermodynamic equilibrium and/or kinetics" of "co-located reductant and oxidant" or "element or isotope fractionations indicative of metabolism". Which sound a whole lot like a detection of a biosignature, which "astrobiologists distinguish" from direct detection . :) I suspect direct detection in an astrobiological context must mean either "direct, as in we physically touched it" or maybe "a signature found using direct imaging". Definitions are hard. :) 1: https://www.liebertpub.com/doi/full/10.1089/ast.2017.1773 https://www.liebertpub.com/doi/full/10.1089/ast.2017.1773
    - adastra22 4y ago
      Direct observation means, well, observing it directly. Seeing living cells in a microscope. Growing it in a Petri dish. Genetic testing, if it turns out it has DNA or RNA like us. Within our own solar system that generally means sample return, or sending people with a full biology lab. For an extrasolar planet? I don't think the astrobiology community is of a single mind regarding what should count as direct observation there. We're not sending people or doing sample return for thousands of years. One common opinion I've heard is that seeing an atmospheric spectrograph indicating the presence of biomarkers like oxygen and methane within the habitable zone would be a bio signature, but multi pixel imaging of the planet would be required to claim direct observation. I'm not sure this is a very strong scientific distinction, however. I'm not an astrobiologist btw, but I used to work at astrobiology.nasa.gov. Small world!