The Triton‐Neptune plasma interaction

The Voyager 2 encounter with Neptune and Triton in August 1989 showed a large ionosphere at Triton. Subsequent studies have tried to explain the production of such high levels of ionization but have ignored the possible plasma dynamics originating from the interaction between Neptune's magnetosphere and Triton. This study applies knowledge gained from studying the solar wind‐Venus interaction to this case. We find that observations made by Voyager 2 can be explained by downward convection of magnetospheric plasma into Triton's atmosphere, with the flow momentum transferred to the neutral atmosphere near an altitude of 650 km. We show that momentum transfer is accomplished as both the convective velocity and the magnetic field go to zero. The mechanism by which the ionosphere is produced was identified previously as impact ionization from hot electrons originating in Neptune's magnetosphere. These precipitating hot electrons are shown in this study to be unaffected by a magnetic field below roughly 650 km. This is a result not previously anticipated, and one which implies that the plasma interaction between Neptune's magnetosphere and Triton cannot be ignored.