Initial analysis of the Voyager PLS data acquired during the Neptune flyby indicates that the thermal plasma in the magnetosphere of Neptune is of Triton origin. Further analysis also shows that although the plasma is moving inwards, its temperature does not increase in both the Triton torus region and near closest approach in accordance with what would be expected for adiabatic motion. Vytenis Vasyliunas, John Richardson and I have published a paper(postscript) in JGR in which we show that this can be understood to be a result of the presence of a cloud of neutral atomic hydrogen of Triton origin in the magnetosphere. In the light of our success with the ion profiles, we are continuing our studies of the electron temperatures observed by Voyager PLS which are also highly anomalous and seem to involve even more complex physical processes.
An equally interesting question is the fine tuning of the aeronomy of
Triton with the PLS findings in the magnetosphere. This question arises
wherever a satellite with an atmosphere interacts with a magnetosphere
and its analysis will engender an interesting comparative
magnetospheres study between Saturn (Titan), Jupiter (Io, Europa) and
Neptune (Triton). We expect to produce a generic picture of such a
configuration.