Evidence of planetary Oxygen and Carbon ions in the outer flank of Venusmagnetosheath

On August 10, 2021, the Mercury-bound BepiColombo spacecraft flew for the second time by Venus for a Gravity-Assist Maneuver. During this second flyby of Venus, a limited number of instruments were turned on, allowing unique observations of the planet and its environment. Among these instruments, the Mass Spectrum Analyzer (MSA) that is part of the particle analyzer consortium onboard the magnetospheric orbiter (Mio) was able to acquire its first plasma composition measurements in space. As a matter of fact, during a limited time interval upon approach of the planet, substantial ion populations were recorded by MSA, with characteristic energies ranging from about 20 eV up to a few hundreds of eVs. Comparison of the measured Time-Of-Flight spectra with calibration data reveals that these populations are of planetary origin, containing both Oxygen and Carbon ions. The Oxygen observations are to some extent consistent with previous in situ measurements from mass spectrometers onboard Venus Express and Pioneer Venus Orbiter. On the other hand, the MSA data provide the first ever in situ evidences of Carbon ions in the near-Venus environment at about 6 planetary radii. We show that the abundance of C+ amounts to about ~30% of that of O+. Furthermore, Changes in the orientation of the magnetic field suggest that these planetary ions are located in the distant magnetosheath flank in the immediate vicinity of the bow-shock region.