Solar wind-Pluto interaction revised

Abstract

The interaction of the solar wind (SW) with Pluto's atmosphere at about 30 AU is studied by means of both 2D bi-ion fluid and hybrid code simulations taking into account that the characteristic size of the interaction region is much smaller than the pick-up radius of the planetary ions. This is due to the weak magnetic field (B ≈ 0.1 nT) and the strongly reduced ionization rate of the planetary molecules ( ν ph ≈ 10 −9s −1) at these large distances from the Sun. The results are the following: For weak production rates (q ≈ 10 27s −1) the planetary ions are forced to move on cyclodial orbits, like in the solar wind produced test particles. Higher productivity leads to a structuring of all parameters due to bi-ion discontinuities which arise in the source region by the relative drift between both ion fluids. Further increase of the heavy ion production leads to the generation of a comet-like tail. Only for the largest production rates found in the literature a detached bow shock as predicted from one-fluid massloading models (Bagenal and McNutt, 1989) is formed. For moderate conditions, the fast pick-up of the newly generated heavy ions by the solar wind prevents the formation of a well developed ionosphere.