A new 3D model of Europas tenuous atmosphere

To support future missions to Europa, such as Europa Clipper and JUICE, physics-based models for Europas neutral gas are in demand. Various physical and chemical processes need to be included in such models. H2O is expected to be the major sputtered species produced by bombardment of magnetospheric energetic ions on the icy surface of Europa. The dissociated products of H2O undergo chemical reactions further to produce O2 and H2. In addition to ion sputtering, sublimation of water ice is another mechanism to supply H2O to the atmosphere. Photochemical reactions and electron impact reactions serve as the primary loss mechanism of H2O and other molecular species and the source mechanism of OH, O, H. In this work, we developed a new 3D model of Europas tenuous atmosphere using the Direct Monte Carlo Simulation (DSMC) method to simulate Europas atmosphere under conditions ranging from the collisionless regime (Kn>>1) to the quasi-collisional regime (Kn~0.1) with the physical and chemical processes described above. Results from a Europa MHD model are fed into the neutral gas model to provide ion density on the surface to compute the ion sputtering rates, and electron density and energy distributions in the whole domain to calculate the electron impact reactions. Preliminary results will be presented, and comparison between the model results and observations will be made. Support for this work is provided by NASA grant 80NSSC20K0854 from the Solar System Workings program.