Finding Signs of Life on Earth-like Planets: High-resolution Transmission Spectra of Earth through time around FGKM stars

TL;DR

This paper provides a comprehensive high-resolution transmission spectra database of Earth-like planets at different geological stages and around various star types, aiding the search for extraterrestrial biosignatures.

Contribution

It introduces the first extensive spectral database for Earth-like planets throughout Earth's history and around diverse host stars, supporting observational strategies for detecting signs of life.

Findings

Biosignature pairs O2 + CH4 and O3 + CH4 indicate biospheres at 1% modern oxygen levels.

Spectral features vary with Earth's atmospheric evolution and host star type.

The database covers 0.4 to 20 microns and is publicly available for research and observation planning.

Abstract

The search for life in the universe mainly uses modern Earth as a template. However, we know that Earth's atmospheric composition changed significantly through its geological evolution. Recent discoveries show that transiting, potentially Earth-like exoplanets orbit a wide range of host stars, which strongly influence their atmospheric composition and remotely detectable spectra. Thus, a database for transiting terrestrial exoplanet around different host stars at different geological times is a crucial missing ingredient to support observational searches for signs of life in exoplanet atmospheres. Here, we present the first high-resolution transmission spectra database for Earth-like planets, orbiting a wide range of host stars, throughout four representative stages of Earth's history. These correspond to a prebiotic high CO2-world - about 3.9 billion years ago in Earth's history - and three epochs through the rise of oxygen from 0.2% to modern atmospheric levels of 21%. We demonstrate that the spectral biosignature pairs O2 + CH4 and O3 + CH4 in the atmosphere of a transiting Earth-like planet would show a remote observer that a biosphere exists for oxygen concentrations of about 1% modern Earth's - corresponding to about 1 to 2 billion years ago in Earth's history - for all host stars. The full model and high-resolution transmission spectra database, covering 0.4 to 20microns, for transiting exoplanets - from young prebiotic worlds to modern Earths-analogs - orbiting a wide range of host stars is available online. It can be used as a tool to plan and optimize our observation strategy, train retrieval methods, and interpret upcoming observations with ground- and space-based telescopes.