Epistemology and anomaly detection in astrobiology

Abstract

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. * We are very grateful to Artemy Kolchinsky for detailed feedback on an earlier draft of this paper, to David Wolpert for helpful discussions, and to audiences at Philosophy of Biology at the Mountains hosted by the University of Utah, and the Uncovering the Laws of Life Workshop in Grindavik, Iceland. Christopher Kempes' work on this project was supported by CAF Canada and the National Aeronautics and Space Administration (Grant No. 80NSSC18K1140).1 There is a rich recent tradition of philosophical commentary on astrobiology, not all of which we are able to comment on here; see for instance Fry (2000), Chela-Flores (2011), andDick (2012).

Searching for Novel Chemistry in Exoplanetary Atmospheres Using Machine Learning for Anomaly Detection

“…By comparison, our approach is completely agnostic, since we do not assume any specific knowledge about the chemistry of the observed planet, nor do we identify the reason why the spectrum appears anomalous. Other discussions of anomalous exoplanets in the literature were based on already measured chemical compositions (Kinney & Kempes 2022) or used general planetary characteristics in lieu of spectroscopic observations (Sarkar et al 2022).…”

Life detection in a universe of false positives

“…[1,[8][9][10][11][12] In the face of this uncertainty, arguments have been made to focus attention on universal features of life (even if these features are not unique to life), [13] or on finding surprising measurements (anomalies) without clearly categorizing those anomalies as having anything to do with life. [1,14] In contrast to previous literature, this work is focused on: (1) how to work on life detection without defining life or constructing a theory of biology; (2) identifying features of life with no known false positives, rather than universal features of life; (3) life detection itself, as opposed to mere anomaly detection.…”