  Exoplanet science promises a continued rapid accumulation of new observations
in the near future, energizing a drive to understand and interpret the
forthcoming wealth of data to identify signs of life beyond our Solar System.
The large statistics of exoplanet samples, combined with the ambiguity of our
understanding of universal properties of life and its signatures, necessitate a
quantitative framework for biosignature assessment Here, we introduce a
Bayesian framework for guiding future directions in life detection, which
permits the possibility of generalizing our search strategy beyond
biosignatures of known life. The Bayesian methodology provides a language to
define quantitatively the conditional probabilities and confidence levels of
future life detection and, importantly, may constrain the prior probability of
life with or without positive detection. We describe empirical and theoretical
work necessary to place constraints on the relevant likelihoods, including
those emerging from stellar and planetary context, the contingencies of
evolutionary history and the universalities of physics and chemistry. We
discuss how the Bayesian framework can guide our search strategies, including
determining observational wavelengths or deciding between targeted searches or
larger, lower resolution surveys. Our goal is to provide a quantitative
framework not entrained to specific definitions of life or its signatures,
which integrates the diverse disciplinary perspectives necessary to confidently
detect alien life.
