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Atmospheric effects of stellar cosmic rays on Earth-like exoplanets orbiting M-dwarfs | | F. Tabataba-Vakili
; J. L. Grenfell
; J.-M. Grießmeier
; H. Rauer
; | | Date: |
16 Nov 2015 | | Abstract: | M-dwarf stars are generally considered favourable for rocky planet detection.
However, such planets may be subject to extreme conditions due to possible high
stellar activity. The goal of this work is to determine the potential effect of
stellar cosmic rays on key atmospheric species of Earth-like planets orbiting
in the habitable zone of M-dwarf stars and show corresponding changes in the
planetary spectra. We build upon the cosmic rays model scheme of Grenfell et
al. (2012), who considered cosmic ray induced NOx production, by adding further
cosmic ray induced production mechanisms (e.g. for HOx) and introducing primary
protons of a wider energy range (16 MeV - 0.5 TeV). Previous studies suggested
that planets in the habitable zone that are subject to strong flaring
conditions have high atmospheric methane concentrations, while their ozone
biosignature is completely destroyed. Our current study shows, however, that
adding cosmic ray induced HOx production can cause a decrease in atmospheric
methane abundance of up to 80\%. Furthermore, the cosmic ray induced HOx
molecules react with NOx to produce HNO$_3$, which produces strong HNO$_3$
signals in the theoretical spectra and reduces NOx-induced catalytic
destruction of ozone so that more than 25\% of the ozone column remains. Hence,
an ozone signal remains visible in the theoretical spectrum (albeit with a
weaker intensity) when incorporating the new cosmic ray induced NOx and HOx
schemes, even for a constantly flaring M-star case. We also find that HNO$_3$
levels may be high enough to be potentially detectable. Since ozone
concentrations, which act as the key shield against harmful UV radiation, are
affected by cosmic rays via NOx-induced catalytic destruction of ozone, the
impact of stellar cosmic rays on surface UV fluxes is also studied. | | Source: | arXiv, 1511.4920 | | Services: | Forum | Review | PDF | Favorites | |
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