4 ms·

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 s

by 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!
- floxy 4y ago
  > multi pixel imaging of the planet would be required to claim direct observation. Here is an interesting proposal for direct imaging of an exoplanet with 1 km resolution: https://arxiv.org/abs/1802.08421 https://arxiv.org/abs/1802.08421 ...and an interesting youtube video about it: https://www.youtube.com/watch?v=NQFqDKRAROI https://www.youtube.com/watch?v=NQFqDKRAROI
  - adastra22 4y ago
    It's a cool idea. Unfortunately getting something out to 550 AU and stopping there would take the better part of a century even with advanced technology. And once you're there, you're really stuck in terms of what you can look at. You can only see what's on the other side of the sun, and with an orbital period of 12800 years, it's not like you're going to sweep out much of the sky in a reasonable timeframe.
    - floxy 4y ago
      If you skip to 14:38 in the video, they describe the solar sails that are supposed to be able to accelerate things to 22 AU/year, which get things to 550AU in 25 years. But yes, you are only going to be able to look at one thing once you get there. https://www.youtube.com/watch?v=NQFqDKRAROI&t=883s https://www.youtube.com/watch?v=NQFqDKRAROI&t=883s

by loxias 4y ago

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!

floxy 4y ago
> multi pixel imaging of the planet would be required to claim direct observation. Here is an interesting proposal for direct imaging of an exoplanet with 1 km resolution: https://arxiv.org/abs/1802.08421 https://arxiv.org/abs/1802.08421 ...and an interesting youtube video about it: https://www.youtube.com/watch?v=NQFqDKRAROI https://www.youtube.com/watch?v=NQFqDKRAROI
- adastra22 4y ago
  It's a cool idea. Unfortunately getting something out to 550 AU and stopping there would take the better part of a century even with advanced technology. And once you're there, you're really stuck in terms of what you can look at. You can only see what's on the other side of the sun, and with an orbital period of 12800 years, it's not like you're going to sweep out much of the sky in a reasonable timeframe.
  - floxy 4y ago
    If you skip to 14:38 in the video, they describe the solar sails that are supposed to be able to accelerate things to 22 AU/year, which get things to 550AU in 25 years. But yes, you are only going to be able to look at one thing once you get there. https://www.youtube.com/watch?v=NQFqDKRAROI&t=883s https://www.youtube.com/watch?v=NQFqDKRAROI&t=883s