A Review of Exoplanetary Biosignatures

TL;DR

This review discusses the current understanding of atmospheric biosignatures in exoplanets, focusing on gases like O2, O3, N2O, and CH4, and considers their detection and abiotic sources based on Solar System and Earth analogs.

Contribution

It synthesizes knowledge on biosignature gases, their formation, detection challenges, and the role of space missions, providing a comprehensive overview of exoplanet biosignature research.

Findings

Identifies key biosignature gases and their abiotic sources.

Analyzes detectability issues of atmospheric biosignatures.

Summarizes space agency plans for biosignature detection.

Abstract

We review the field of exoplanetary biosignatures with a main focus upon atmospheric gas-phase species. Due to the paucity of data in Earth-like planetary atmospheres a common approach is to extrapolate knowledge from the Solar System and Early Earth to Earth-like exoplanets. We therefore review the main processes (e.g. atmospheric photochemistry and transport) affecting the most commonly-considered species (e.g. O2, O3, N2O, CH4 etc.) in the context of the modern Earth, Early Earth, the Solar System and Earth-like exoplanets. We consider thereby known abiotic sources for these species in the Solar System and beyond. We also discuss detectability issues related to atmospheric biosignature spectra such as band strength and uniqueness. Finally, we summarize current space agency roadmaps related to biosignature science in an exoplanet context.