ELECTRON-TEMPERATURE PROFILES IN THE MAGNETOSPHERE OF NEPTUNE

The electron temperature in the magnetosphere of Neptune decreases wit h decreasing radial distance over the same distance range over which a similar decrease of the proton temperature has been explained as resu lting from interaction of protons with a cloud of neutral hydrogen. Th e effect on the electron temperature of the interaction with this clou d is studied, taking into account photoionization, electron Impact ion ization, radiation, and electron-ion Coulomb collisions. It is found t hat the electron temperature should decrease with decreasing distance, in agreement with observations, but that at the outer boundary the th eoretically expected electron temperatures are considerably lower than what is observed, implying a heating process or a source of hot elect rons which have not yet been unambiguously identified. In the inner re gion, where the adiabatic increase of the proton temperature has been taken as implying the absence of any significant density of neutral at oms, the electron temperature remains essentially constant, implying a powerful cooling process that acts only on electrons. This process is also at present an object of speculation; as a possibility, thermal c oupling to the ionosphere via strong pitch angle diffusion of electron s is suggested. (C) 1997 Elsevier Science Ltd.