The origin of molecular ions in the Martian magnetosphere

Abstract

Hot plasma measurements from the instrument ASPERA on the Sovist Phobos-2 spacecraft indicate a large density of molecular ions in the Martian magnetosphere and thus a high outflow of the molecular species. This is an unexpected result since it is generally believed that the molecular ions in the Martian ionosphere are in photochemical equilibrium and these remain undisturbed by the solar wind. On the basis of knowledge geined from the Radio occulation measurements on the Pioneer Venus during solar minimum, we demonstrate that the O₂⁺ profiles observed by the Viking landers at Mars have been grossly eroded by the solar wind. This erosion takes place down to an altitude of 160 km and thus contributes to the high outflow' of the molecular species.