title: Biomarker response to galactic cosmic ray-induced NOx and the methane greenhouse effect in the atmosphere of an Earth-like planet orbiting an M dwarf star.
abstract: Planets orbiting in the habitable zone of M dwarf stars are subject to high levels of galactic cosmic rays (GCRs), which produce nitrogen oxides (NOx) in Earth-like atmospheres. We investigate to what extent these NO(Mx) species may modify biomarker compounds such as ozone (O3) and nitrous oxide (N2O), as well as related compounds such as water (H2O) (essential for life) and methane (CH4) (which has both abiotic and biotic sources). Our model results suggest that such signals are robust, changing in the M star world atmospheric column due to GCR NOx effects by up to 20% compared to an M star run without GCR effects, and can therefore survive at least the effects of GCRs. We have not, however, investigated stellar cosmic rays here. CH4 levels are about 10 times higher on M star worlds than on Earth because of a lowering in hydroxyl (OH) in response to changes in the ultraviolet. The higher levels of CH4 are less than reported in previous studies. This difference arose partly because we used different biogenic input. For example, we employed 23% lower CH4 fluxes compared to those studies. Unlike on Earth, relatively modest changes in these fluxes can lead to larger changes in the concentrations of biomarker and related species on the M star world. We calculate a CH4 greenhouse heating effect of up to 4K. O3 photochemistry in terms of the smog mechanism and the catalytic loss cycles on the M star world differs considerably compared with that of Earth.
authors.affiliation: Institut für Planetenforschung, Extrasolare Planeten und Atmosphären, Deutsches Zentrum für Luft- und Raumfahrt, Berlin, Germany. Lee.Grenfell@dlr.de
authors.forename: John Lee
authors.initials: JL
authors.lastname: Grenfell
authors.forename: Jean-Mathias
authors.initials: JM
authors.lastname: Griessmeier
authors.forename: Beate
authors.initials: B
authors.lastname: Patzer
authors.forename: Heike
authors.initials: H
authors.lastname: Rauer
authors.forename: Antigona
authors.initials: A
authors.lastname: Segura
authors.forename: Anja
authors.initials: A
authors.lastname: Stadelmann
authors.forename: Barbara
authors.initials: B
authors.lastname: Stracke
authors.forename: Ruth
authors.initials: R
authors.lastname: Titz
authors.forename: Philip
authors.initials: P
authors.lastname: Von Paris
mesh_terms: D055580:Astronomical Phenomena; D001256:Astronomy; D001272:Atmosphere; D015415:Biomarkers / Q000032:analysis; D003359:Cosmic Radiation; D018559:Exobiology; D005118:Extraterrestrial Environment; D017752:Greenhouse Effect; D008697:Methane / Q000528:radiation effects*; D009589:Nitrogen Oxides / Q000528:radiation effects*; D010126:Ozone / Q000528:radiation effects; D016083:Planets; D018561:Space Simulation
chemical_list: D015415:Biomarkers; D009589:Nitrogen Oxides; D010126:Ozone; D008697:Methane