Quantifying the information impact of future searches for exoplanetary biosignatures

TL;DR

This paper uses Bayesian analysis to evaluate how future exoplanet biosignature searches could influence our beliefs about the prevalence of life in the universe, highlighting the impact of potential discoveries or non-detections.

Contribution

It introduces a Bayesian framework to quantify how future biosignature searches will alter our understanding of life's frequency in the galaxy, considering detection and non-detection scenarios.

Findings

A single biosignature detection would greatly increase the estimated number of inhabited planets.

Non-detections would have minimal impact on current beliefs about life's abundance.

Detection could suggest over 100,000 inhabited planets with high confidence.

Abstract

One of the major goals for astronomy in the next decades is the remote search for biosignatures (i.e.\ the spectroscopic evidence of biological activity) in exoplanets. Here, we adopt a Bayesian statistical framework to discuss the implications of such future searches, both in the case when life is detected, and when no definite evidence is found. We show that even a single detection of biosignatures in the vicinity of our stellar system, in a survey of similar size to what will be obtainable in the next two decades, would affect significantly our prior belief on the frequency of life in the universe, even starting from a neutral or pessimistic stance. In particular, after such discovery, an initially agnostic observer would be led to conclude that there are more than $10^5$ inhabited planets in the galaxy with a probability exceeding $95$\%. However, this conclusion would be somewhat weakened by the viability of transfer of biological material over interstellar distances, as in panspermia scenarios. Conversely, the lack of significant evidence of biosignatures would have little effect, leaving the assessment of the abundance of life in the galaxy still largely undetermined.