The Role of Atmospheric Exchange in False-Positive Biosignature Detection

TL;DR

This study investigates how atmospheric exchange could cause false-positive biosignature detections on exoplanets like TRAPPIST-1 e, finding that such false positives require implausibly high external oxygen and water influxes.

Contribution

It models the impact of external atmospheric influxes on biosignature detection and assesses the detectability of abiotic oxygen and ozone with future telescopes.

Findings

False-positive biosignatures require unrealistically high external fluxes.

Simulated spectral observations show abiotic O2/O3 are distinguishable from biotic sources.

Detectability thresholds are well above plausible atmospheric exchange levels.

Abstract

Saturn's Moon Titan receives volatiles into the top of its atmosphere-including atomic oxygen-sourced from cryovolcanoes on Enceladus. Similar types of atmosphere exchange from one body to another, such as O2 and O3 sourced from TRAPPIST-1 d, could be introduced into the upper atmosphere of TRAPPIST-1 e and might be interpreted as biosignatures. We simulate this potential false-positive for life on TRAPPIST-1 e, by applying an external influx of water and oxygen into the top of the atmosphere using a coupled 1-D photochemical-climate model (Atmos), to predict atmospheric composition. In addition, synthetic spectral observations are produced using the Planetary Spectrum Generator for the James Webb Space Telescope, Origins Space Telescope, Habitable Exoplanet Observatory and Large Ultra-violet/Optical/Infrared Surveyor to test the detectability of abiotic-generated O2 and O3 in the presence of abiotic and biotic surface fluxes of CH4. We determine that the incoming flux of material needed to trigger detection of abiotic O2/O3 by any of these observatories is more than two orders of magnitude (1E12 molecules/cm2/s) above what is physically plausible.