HOT OXYGEN CORONA AT EUROPA

A model of the hot oxygen exosphere at Europa was constructed. The sou rce term for the hot atoms was assumed to be dissociative recombinatio n of O-2(+) and Liouville's theorem was used to calculate their altitu de distribution. It was found that near the surface the hot oxygen den sity is in excess of 200 cm(-3), dropping to a value on the order of 5 0 cm(-3) at 1500 km. These calculations indicate that the hot atomic o xygen densities are considerably less than the thermal molecular oxyge n ones, but slightly larger than the measured sodium values. The escap e flux of the hot oxygen atoms was calculated to be on the order of 1. 4x10(8) atoms cm(-2) sed(-1). This corresponds to a global escape rate of 4.4x10(25) atoms sec(-1), which is more than an order of magnitude less than the estimated atmospheric sputtering rate.