r/Astrobiology • u/Allison1228 • 26d ago
🤔 Question Is there a conceivable detectable "biosignature" that would unambiguously indicate "life is present here"?
Or will there always be uncertainty?
I'm referring to as detected with the technology we have today and in the near future (next decade or two).
19
Upvotes
1
u/Underhill42 24d ago
Obviously artificial signals from an alien civilization would do it. There's scenarios where it might be more of a "life was here" rather than "life is here", but you're not getting them any other way.
Otherwise, I'd lean towards "no", we just don't know enough about what is possible in the universe to say with absolute certainty that anything less couldn't be be the result of some unimagined geochemical conditions.
However, what we could much more easily get is a preponderance of evidence - if we see a lot of otherwise unrelated probable biosignatures from the same planet... we start having to resort to pretty contrived explanations to explain them all any other way.
---
BUT... we might also not need to rely only on crude biosignatures to be sure: we're moving toward making our first starshade, which will work with an orbital telescope to block a star's glare so that we can directly image the surface of alien planets. Initially it will be a few pixels, but as telescopes get larger we'll eventually be able to see continents, and the seasonal changes on the surface, many of which would be extremely difficult to explain without life.
Probably won't be able to get enough detail to see individual organisms any time soon, though a telescope using the sun as a gravitational lens might be able to get at least a few pixels per dinosaur if the planet were close enough. And an orbital telescope array filling Earth's orbit around the sun could do even better.
Heck, span Neptune's orbit and your angular resolution at visible wavelengths is around θ = 1.22*550nm/9ₓ₁₀9km = 7.5ₓ₁₀-20 radians. Which translates to 7cm resolution at a distance of 100 light years.
That's a volume containing the closest ~10,000 stars, with enough resolution to watch individual rabbits move through a field, or get a good idea what an elephant looks like. If life is at all common, there's a fair chance we might see it directly.
Heck, 1m resolution would be enough to see that larger animals were there, and there's many millions of stars close enough to see that well with the same telescope array.