Observations of Mercury’s Exosphere during BepiColombo First Mercury Flyby with PHEBUS’ visible channels
Abstract
During the first flyby of Mercury with BepiColombo in October 2021, the ultraviolet spectrometer PHEBUS (Probing of Hermean Environment By Ultraviolet Spectroscopy) was able to observe with the two visible channels centered at 404 nm (K line) and 422 nm (Ca line). The observation started 30 minutes before Closest Approach and lasted one hour. The results clearly depict the geometry of observation, the spacecraft moving from the nightside of Mercury to its dayside. We also see some bursts on the count rate after the exit of Mercury’s shadow, and discuss possible correlations with dust particles or the crossing of magnetospheric structures. We distinctly detect Calcium at 422nm and compare these results with MESSENGER data and an exospheric model.