FIG. 1.

A Bayesian framework for biosignature assessment. Spectral and/or photometric data that may contain biosignatures are used with models to find likelihoods given the context of the exoplanet, for example, its astrophysical environment. One likelihood is the conditional probability of those data occurring given the context and the hypothesis that the exoplanet has life. Another likelihood is the probability of the data occurring given the context and the hypothesis that the exoplanet has no life. These two likelihoods are weighted by prior knowledge to provide a best-informed (posterior) probability that the exoplanet has life given the spectral and/or photometric data and context. Blue boxes signify data acquisition. Yellow boxes contain conditional probabilities and prior probabilities that are part of Bayes' Theorem (gray oval), which is expressed in Eq. 7 in the text.