A new model suite to determine the influence of cosmic rays on (exo)planetary atmospheric biosignatures

Validation based on modern Earth

¹ Institut für Experimentelle and Angewandte Physik, Christian-Albrechts-Universität zu Kiel (CAU), 24118 Kiel, Germany
e-mail: herbst@physik.uni-kiel.de
² Institut für Planetenforschung (PF), Deutsches Zentrum für Luft- und Raumfahrt (DLR), Rutherfordstr. 2, 12489 Berlin, Germany
³ Institut für Meteorologie und Klimaforschung, Karlsruher Institut für Technologie (KIT), Hermann-von Helmholtz Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
⁴ Zentrum für Astronomie und Astrophysik, Technische Universität Berlin (TUB), Hardenbergstrasse 36, 10623 Berlin, Germany
⁵ Alfred Wegener Institut, Helmholtz Zentrum für Polar- und Meeresforschung, Telegrafenberg A45, 14473 Potsdam, Germany
⁶ Institut für Methodik der Fernerkundung, Deutsches Zentrum für Luft- und Raumfahrt (DLR), 82234 Oberpfaffenhofen, Germany

Received: 14 May 2019
Accepted: 13 September 2019

Abstract

Context. The first opportunity to detect indications for life outside of 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 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.

Aims. 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.

Methods. We describe newly combined state-of-the-art modeling tools to study the impact of the radiation and particle environment, in particular of cosmic rays, on atmospheric particle interaction, 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.

Results. In addition to comparing our results to Earth-bound measurements, we investigate the ozone production and -loss cycles as well as the atmospheric radiation dose profiles during quiescent solar periods and during the strong solar energetic particle event of February 23, 1956. Further, the scenario-dependent terrestrial transit spectra, as seen by the NIR-Spec infrared spectrometer onboard the JWST, are modeled. Amongst others, we find that the comparatively weak solar event drastically increases the spectral signal of HNO₃, 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.