The Diversity of Exoplanetary Environments and the Search for Signs of Life Beyond Earth

TL;DR

This paper discusses the vast diversity of exoplanetary environments, emphasizing the importance of considering various atmospheric compositions and habitats in the search for extraterrestrial life with upcoming telescopic technologies.

Contribution

It reviews potential habitats and biosignature indicators across diverse exoplanet environments, expanding the scope of habitable conditions beyond Earth-like planets.

Findings

Bacteria can survive in high concentrations of H2, He, CO2, and CO.

Life may exist in alternative solvents and cloud biospheres.

Next-generation telescopes will enhance exoplanet habitability studies.

Abstract

Thousands of exoplanets orbit nearby stars, showcasing a remarkable diversity in mass, size, and orbits. With the James Webb Space Telescope now operational, we are observing exoplanet atmospheres and aiming to reach down to small, habitable-zone exoplanets in search of signs of habitability and possibly even biosignature gases. Given the scarcity of targets, it is imperative to embrace the known diversity and consider the range of exoplanets that might host life. We review how Earth life interacts with various atmospheric gases, noting that bacteria can survive in high concentrations of gases such as H2, He, CO2, and CO. Additionally, we consider the potential for life in alternative solvents and in cloud biospheres where rocky surfaces are excessively hot, as well as in hypothesized planetary global oceans. We highlight that life fundamentally requires metal ions for catalytic reactions, suggesting that environments without surface contact need meteoritic delivery to provide these essential elements. Despite today's observational limits, a suite of next-generation telescopes is being designed specifically for exoplanet studies, promising to expand our capabilities and understanding in the future.