Biomarker Response to Galactic Cosmic Ray-Induced NOx and the Methane Greenhouse Effect in the Atmosphere of an Earthlike Planet Orbiting an M-Dwarf Star

摘要

Planets orbiting in the habitable zone (HZ) of M-Dwarf stars are subject tohigh levels of galactic cosmic rays (GCRs) which produce nitrogen oxides inearthlike atmospheres. We investigate to what extent this NOx may modifybiomarker compounds such as ozone (O3) and nitrous oxide (N2O), as well asrelated compounds such as water (H2O) (essential for life) and methane (CH4)(which has both abiotic and biotic sources) . Our model results suggest thatsuch signals are robust, changing in the M-star world atmospheric column by upto 20% due to the GCR NOx effects compared to an M-star run without GCR effectsand can therefore survive at least the effects of galactic cosmic rays. We havenot however investigated stellar cosmic rays here. CH4 levels are about 10times higher than on the Earth related to a lowering in hydroxyl (OH) inresponse to changes in UV. The increase is less than reported in previousstudies. This difference arose partly because we used different biogenic input.For example, we employed 23% lower CH4 fluxes compared to those studies. Unlikeon the Earth, relatively modest changes in these fluxes can lead to largerchanges in the concentrations of biomarker and related species on the M-starworld. We calculate a CH4 greenhouse heating effect of up to 4K. O3photochemistry in terms of the smog mechanism and the catalytic loss cycles onthe M-star world differs considerably compared with the Earth.