DIX Planetary Science Seminar
Europa experiences day and night every 3.5 Earth days, resulting in a diurnal cycle directly affecting its water product exosphere. The majority of the exosphere is thought to be composed of molecular oxygen and water vapor, both of which have been identified to vary in ultraviolet and optical auroral observations. We study the mechanisms driving the diurnal variability seen on Europa, some of which are common also to Ganymede. 3-D exosphere general model (EGM) simulations output specific orbital phases that would be amenable to distinguishing a transient, localized atmosphere during Europa Clipper flybys. We find considerable orbital evolution of Europa's atmospheric species, especially in Jupiter's shadow, under various assumptions on sublimation, sputtering, and thermal outgassing. In particular, if line-of-sight column densities exceed 1014/cm2 during sunlit leading hemisphere phases, a tidally-heated geologic source may be required. The water column density maps presented here serve as a background exosphere which enables the search for, and characterization of trace species, some of which carry astrobiologic potential. Our exospheric technique is critical also for cold ocean exoplanets (e.g. Habitable World Observatory) which, due to their trivial scale height, have no canonical avenue for characterization. Sodium exospheres in particular, well known at Io & Europa, are bright enough that we currently see spectral indications of a small satellite at an extrasolar gas giant system that exhibits similar behavior to Europa entering eclipse.