Phobos-2 results on the ionospheric plasma escape from Mars

The outflow of ions from the Martian ionosphere was studied by the ASPERA instrument on the Soviet Phobos-2 spacecraft. The Martian magnetosphere tail is found to be dominated by plasma of Martian origin, primarily atomic oxygen and exospheric hydrogen, but also with a substantial admixture of molecular ions. The ionospheric plasma escape may be related with several different processes, one which is similar to that near magnetized bodies (e.g. the Earth), and another that usually dominates near non-magnetized bodies (e.g. comets). The loss rate of the ionospheric ion outflow is very high, about 1 kg/s. This value corresponds to an erosion of the Martian atmosphere in about 100 million years. Thus, under the assumption that Mars was weakly magnetized also in the past, the solar wind interaction with its exosphere/ionosphere may have been a major reason for the observed dehydration of Mars.