Non-thermal processes of nitrogen oxide formation during precipitation of auroral electrons into the upper atmospheres of terrestrial planets

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Nitric oxide is a potential biomarker in the N 2 -O 2 atmospheres of terrestrial exoplanets, which can be detected by space missions, including the planned launch of the Russian Spektr-UF observatory. From observations of the Earth's thermosphere in the polar regions, it is known that important sources of formation of this molecule are the precipitation of high-energy electrons into the planet's atmosphere, as well as the non-thermal processes accompanying them. In this paper the non-thermal processes of nitrogen oxide formation in the polar regions of the Earth's upper atmosphere are investigated, as well as the atmospheres of exoplanets located in the potential habitability zone of active stars. For this purpose, a numerical kinetic Monte Carlo model of the interaction of high-energy electrons with atmospheric gas has been developed; a kinetic Monte Carlo model of the interaction of suprathermal N( 4 S) atoms formed as a result of dissociation of N 2 molecules by electron impact with the surrounding gas; as well as a model of odd nitrogen chemistry with taking into account the molecular and turbulent diffusion. According to the results of calculations, it is confirmed that the process of dissociation of N 2 by an electron impact during the interaction of the stellar wind with the atmosphere of the planet is an important source of suprathermal N atoms, which contribute to a significant increase in the non-thermal formation of NO in the N 2 -O 2 atmospheres of terrestrial planets (both locally, in the case of a planet's own magnetic field, and throughout the planet's surface, in the case of its absence). Because the column concentration of NO during flares becomes larger, therefore the chances of detecting of nitric oxide biomarker in the atmospheres of the terrestrial-type exoplanets located in the potential habitability zone of active stars are also become larger.