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 Nep tune's magnetosphere and Triton. This study applies knowledge gained f rom studying the solar wind-Venus interaction to this case. We find th at observations made by Voyager 2 can be explained bg downward convect ion of magnetospheric plasma into Triton's atmosphere, with the flow m omentum transferred to the neutral atmosphere near an altitude of 650 km. We show that momentum transfer is accomplished as both the convect ive velocity and the magnetic field go to zero. The mechanism by which the ionosphere is produced was identified previously as impact ioniza tion from hot electrons originating in Neptune's magnetosphere. These precipitating hot electrons are shown in this study to be unaffected b y a magnetic field below roughly 650 km. This is a result not previous ly anticipated, and one which implies that the plasma interaction betw een Neptune's magnetosphere and Triton cannot be ignored.