Epistemology and Anomaly Detection in Astrobiology

We examine the epistemological foundations of a leading technique in the search for evidence of life on exosolar planets. Specifically, we consider the ``transit method'' for spectroscopic analysis of exoplanet atmospheres, and the practice of treating anomalous chemical compositions of the atmospheres of exosolar planets as indicators of the potential presence of life. We propose a methodology for ranking the anomalousness of atmospheres that uses the mathematical apparatus of support vector machines, and which aims to be agnostic with respect to the particular chemical biosignatures of life. We argue that our approach is justified by an appeal to the "hinge" model of epistemic justification first proposed by Wittgenstein (1969). We then compare our approach to previous work due to Walker et al. (2018) and Cleland (2019a, 2019b)