Europa's oxygen exosphere and its magnetospheric interaction

The newly detected oxygen atmosphere of Europa is modeled by invoking charged particle sputtering with H2O and O-2 molecules as the main ejecta. The magnetospheric corotating ions could provide the required source strength (similar to 3 x 10(26) sec(-1)) of O-2 molecules if a fraction (similar to 20%) of the exospheric ions were recycled to Europa's surface where they produce additional sputtering product, Two exospheric components are expected to form: an extended corona with a size of a few satellite radii which is composed of sputtered molecules in ballistic motion, and a thermal population with a surface density of 10(8)-10(9) cm(-3) and a scale height of about 20 km. The electron impact ionization of this exosphere would lead to an Io-like interaction with the jovian magnetosphere with a field-aligned Birkeland current of about 5 x 10(5) A. (C) 1996 Academic Press, Inc.