Europa's Oxygen Exosphere and Its Magnetospheric Interaction

Abstract

The newly detected oxygen atmosphere of Europa is modeled by invoking charged particle sputtering with H2O and O2molecules as the main ejecta. The magnetospheric corotating ions could provide the required source strength (∼3 × 1026sec−1) of O2molecules if a fraction (∼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 108–109cm−3and 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 × 105A.