Pick-up ions at Pluto

Abstract

Methane molecules escaping from Pluto's atmosphere are ionized, and the resulting ions are picked up by the solar wind. The mass loading associated with this ion pick-up can produce a cometlike interaction of the solar wind with Pluto. Heavy ion gyroradii are as large as a half million km in the weak interplanetary magnetic field that exists at 30 AU, which is about an order of magnitude larger than the size of the 'interaction region'. We have calculated velocity space distributions of pick-up ions using numerically determined ion trajectories. The predicted pick-up ion fluxes are high enough to be detectable by standard charged particle detectors as far upstream of Pluto as 10 exp 6 km.