Theory 08/Exoplanet atmospheres/Transit spectroscopy
Life Is a Disequilibrium
The claim
A biosphere is detectable as a ratio of incompatible gases rather than as any single molecule, so oxygen alone proves little while oxygen with methane proves a source.
01Mechanism
Photochemistry drives atmospheres toward equilibrium; a sustained departure requires a flux that only a surface process can supply.
02Prediction
Biosignature candidates should show correlated disequilibrium.
03Refutation
Abiotic sources sustaining the same ratio would remove the inference.
04What makes it checkable
Transit spectroscopy now measures multiple molecular species in the same atmosphere, so the ratio can be computed rather than assumed from one detection.
05Why it was not testable before
Single-molecule detections were the limit of the technique; the ratio needs simultaneous multi-species spectra.