Possible temperature effects of energetic neutral hydrogen atoms on the Martian exosphere

Abstract

Martian neutral gas temperatures estimated from topside plasma scale heights of electron density distributions and Lyman-α dayglow observations obtained by several Mars missions yield an exospheric temperature in the order of 350 ± 100 K. However, this value would imply a much higher dependence on the F 10.7 radio flux than found for Venus and does not appear to be consistent with the observed solar cycle dependence of the Martian ionospheric peak plasma densities. On the other hand, observations on Venus indicate that photochemically produced very low energetic H atoms, as well as part of the solar wind protons and accelerated planetary H + ions, which can be transformed into energetic H atoms (ENAs) may also contribute to the observed neutral H atoms. By calculating the flux of solar wind ENAs we find that they may give rise to an increase of the exospheric temperature of up to several tens of Kelvin.