LOW-ENERGY IONS NEAR NEPTUNE

This paper provides a synopsis of the ion observations near Neptune, from the upstream solar wind through the magnetosheath, magnetosphere, and back out through the magnetosheath to the solar wind. The main emphasis is on the magnetosphere; complete density and temperature profiles are shown for this region. Observations are consistent with the presence of two ion species, H+ and N+, which increase in density and temperature with decreasing distance from Neptune. Calculations of the flux tube content and energy invariant imply that N+ escapes directly from Triton's ionosphere, whereas H+ is created by ionization of a large neutral H cloud emanating from Triton and extending inward to 8 R(N). Inside L = 8, substantial plasma losses occur, precipitation into Neptune's atmosphere is one loss mechanism, and charge exchange with a hypothesized Neptune-centered H cloud may also be important. Given expected source rates of about 1 X 10(25) ions/s, transport times must be very fast of the order of 10(5) s at L = 10.