Cool Stars 14 - Submitted Abstract # 305 This version created on 05 October 2006 Biomarker Response to Galactic Cosmic Ray-Induced NOx and the Methane Lee Grenfell, Deutsches Zentrum fuer Luft- und Raumfahrt (DLR), Berlin, Germany Jean-Mathias Griessmeier, Observatoire de Paris, Meudon, France Beate Patzer, Technisches Universitat, Berlin, Germany Heike Rauer, Deutsches Zentrum fuer Luft- und Raumfahrt (DLR), Berlin, Germany Antigona Segura, Penn State (presently at IPAC CALTECH), USA Anja Stadelmann, Technisches Universitat, Braunschweig, Germany Barbara Stracke, Deutsches Zentrum fuer Luft- und Raumfahrt (DLR), Berlin, Germany Ruth Titz, Deutsches Zentrum fuer Luft- und Raumfahrt (DLR), Berlin, Germany Philip von Paris, Deutsches Zentrum fuer Luft- und Raumfahrt (DLR), Berlin, Germany Planets orbiting in the habitable zone (HZ) of M-Dwarf stars are subject to high levels of cosmic rays which produce nitrogen oxides in earthlike atmospheres. We investigate to what extent this NOx may perturb biomarker signals. Our model results suggest that the biomarker signals are robust, changing in the M-star atmospheric column by up to 25% due to the GCR NOx effects compared to an M-star run without GCR effects and can therefore survive at least the effects of galactic cosmic rays. We have not however investigated stellar cosmic rays here. Methane (CH4) levels are about x1000 times higher than on the Earth related to a lowering in hydroxyl (OH) in response to changes in UV, as already noted in previous studies. The high CH4 levels produce a large greenhouse effect of 50-60K which has a potentially large effect upon the biomarker columns. ----------------------------------