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 O₂ molecules as the main ejecta. The magnetospheric corotating ions could provide the required source strength (∼3 × 10²⁶ sec^-1) of O₂ molecules 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 10⁸-10⁹ 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 × 10⁵ A.