Spectral Fingerprints of Earth-like Planets Around FGK Stars

TL;DR

This study models the atmospheres and spectra of Earth-like planets orbiting FGK stars, analyzing how stellar temperature and UV radiation influence atmospheric composition and spectral detectability of habitability indicators for future observations.

Contribution

It provides a comprehensive grid of model atmospheres and spectra for Earth-like planets around FGK stars, highlighting the impact of stellar properties on atmospheric features and detectability.

Findings

Higher stellar UV increases atmospheric photolysis and alters gas abundances.

Stellar temperature affects water vapor and spectral feature visibility.

Spectral detectability varies with wavelength and stellar type.

Abstract

We present model atmospheres for an Earth-like planet orbiting the entire grid of main sequence FGK stars with effective temperatures ranging from Teff = 4250K to Teff = 7000K in 250K intervals. We model the remotely detectable spectra of Earth-like planets for clear and cloudy atmospheres at the 1AU equivalent distance from the VIS to IR (0.4 {\mu}m - 20 {\mu}m) to compare detectability of features in different wavelength ranges in accordance with JWST and future design concepts to characterize exo-Earths. We also explore the effect of the stellar UV levels as well as spectral energy distribution on a terrestrial atmosphere concentrating on detectable atmospheric features that indicate habitability on Earth, namely: H2O, O3, CH4, N2O and CH3Cl. The increase in UV dominates changes of O3, OH, CH4, N2O and CH3Cl whereas the increase in stellar temperature dominates changes in H2O. The overall effect as stellar effective temperatures and corresponding UV increase, is a lower surface temperature of the planet due to a bigger part of the stellar flux being reflected at short wavelengths, as well as increased photolysis. Earth-like atmospheric models show more O3 and OH but less stratospheric CH4, N2O, CH3Cl and tropospheric H2O (but more stratospheric H2O) with increasing effective temperature of Main Sequence stars. The corresponding spectral features on the other hand show different detectability depending on the wavelength observed. We concentrate on directly imaged planets here as framework to interpret future lightcurves, direct imaging and secondary eclipse measurements of atmospheres of terrestrial planets in the HZ at varying orbital positions.