NASA Science
Biosignature
A gas or feature in a planet's spectrum that life would explain and geology would struggle to.
No single molecule proves life. The argument is always about disequilibrium: oxygen and methane together, for instance, destroy each other quickly, so finding both means something is continuously replenishing them. Every candidate has an abiotic explanation that has to be excluded first, which is why claims in this area are announced cautiously and disputed loudly. The honest position is that we have detection capability arriving before we have agreement on what would count as a detection. The other half of the problem is statistical. A tentative detection on one planet, at a few sigma, in a spectrum that took a hundred hours of a heavily oversubscribed telescope, cannot be repeated often enough to settle anything — and the community has learned from the 1996 Martian meteorite and the 2020 phosphine claim that the announcement travels considerably further than the retraction.
Where it has come up lately
Related terms
Transit method
Finding planets by watching a star dim slightly as one passes in front.
Radial velocity
Finding planets by the wobble they induce in their star's motion.
Habitable zone
The orbital band where a planet could hold liquid water — no more than that.
Sub-Neptune
The most common kind of planet in the galaxy, and there is not one in our solar system.
Questions
What is Biosignature?
A gas or feature in a planet's spectrum that life would explain and geology would struggle to.
Why does it matter?
The other half of the problem is statistical. A tentative detection on one planet, at a few sigma, in a spectrum that took a hundred hours of a heavily oversubscribed telescope, cannot be repeated often enough to settle anything — and the community has learned from the 1996 Martian meteorite and the 2020 phosphine claim that the announcement travels considerably further than the retraction.