A New Model Suite to Determine the Influence of Cosmic Rays on (Exo)planetary Atmospheric Biosignatures -- Validation based on Modern Earth

TL;DR

This paper introduces a comprehensive modeling suite to assess how cosmic rays and stellar radiation influence atmospheric biosignatures on exoplanets, with validation based on Earth's conditions, crucial for future life detection missions.

Contribution

It develops and combines advanced models to simulate the impact of cosmic rays on exoplanetary atmospheres and biosignatures, providing new insights into their detectability under stellar radiation effects.

Findings

Solar energetic particles increase HNO₃ spectral signals.

Strong solar events suppress ozone spectral features.

Ozone may not be a reliable biosignature for active star systems.

Abstract

The first opportunity to detect indications for life outside the Solar System may be provided already within the next decade with upcoming missions such as the James Webb Space Telescope (JWST), the European Extremely Large Telescope (E-ELT) and/or the Atmospheric Remote-sensing Infrared Exoplanet Large-survey (ARIEL) mission, searching for atmospheric biosignatures on planets in the habitable zone of cool K- and M-stars. Nevertheless, their harsh stellar radiation and particle environment could lead to photochemical loss of atmospheric biosignatures. We aim to study the influence of cosmic rays on exoplanetary atmospheric biosignatures and the radiation environment considering feedbacks between energetic particle precipitation, climate, atmospheric ionization, neutral and ion chemistry, and secondary particle generation. We describe newly-combined state-of-the-art modeling tools to study the impact of the radiation and particle environment on atmospheric particle interaction, the influence on the atmospheric chemistry, and the climate-chemistry coupling in a self-consistent model suite. To this end, models like the Atmospheric Radiation Interaction Simulator (AtRIS), the Exoplanetary Terrestrial Ion Chemistry model (ExoTIC), and the updated coupled climate-chemistry model are combined. Amongst others, we model the atmospheric response during quiescent solar periods and during a strong solar energetic particle event as well as the scenario-dependent terrestrial transit spectra, as seen by the NIR-Spec infrared spectrometer onboard the JWST. We find that the comparatively weak solar event drastically increases the spectral signal of HNO$_3$, while significantly suppressing the spectral feature of ozone. Because of the slow recovery after such events, the latter indicates that ozone might not be a good biomarker for planets orbiting stars with high flaring rates.