A Search for Calcium in the Atmosphere of Europa with Ground-based Telescope

Abstract Europa’s tenuous atmosphere mainly consists of molecular oxygen, with traces of sodium, potassium, and other elements, potentially reflecting the composition of its surface and interior. While sodium- and magnesium-bearing hydrated salts have been suspected to exist on the surface, other materials like calcium-bearing salts dissolved in the subsurface ocean could also be present. Atmospheric emissions could originate from sputtering or sublimation processes, and potential water plume activity, possibly influenced by tidal interactions, could significantly contribute to the atmosphere. Additionally, the composition of the atmosphere and surface could be affected by neighboring moons, particularly Io. We searched for calcium emissions using the Multi-Spectral Imager of a 1.6 m Pirka telescope at Hokkaido University’s Astronomical Observatory. Observations from 2021 September to 2023 October revealed suggestive emission lines attributed to calcium atoms. These suggestive emission lines originated from the trailing hemisphere, suggesting that sputtering is likely the dominant atmospheric source.