During the first flyby of the BepiColombo composite spacecraft at Mercury in October 2021 ion spectrometers observed two intense spectral lines with energies between 10 and 70eV. The spectral lines persisted also at larger distances from Mercury and were ob- served again at lower intensity during cruise phase in March 2022 and at the second and third Mercury flyby as a single band. The ion composition indicates that water is the dominant gas source. The outgassing causes the composite spacecraft to charge up to a negative potential of up to -50V. The distribution and intensity of the lower energy signal depends on the intensity of low energy electron fluxes around the spacecraft which again depend on the magnetic field orientation. We interpret the observation as being caused by water outgassing from different source locations on the spacecraft being ion- ized in two different regions of the surrounding potential. The interpretation is confirmed by two dimensional particle-in-cell simulations.

The ion composition of the tail current sheet is essential to understanding the Martian ion escape, however, our current knowledge is poor. Using measurements by Mars Atmosphere and Volatile EvolutioN (MAVEN), we investigate the density of different ion species in the Martian magnetotail current sheet. We find that events we survey of the current sheet, the average occurrence rate of current sheets with dominant heavy ions (O+ and O2+) is about 50%, while the rate of those with dominant H+ is about 20%. A current sheet closer to the terminator is mostly dominated by heavy ions, regardless of upstream solar wind, but it could be dominated sometimes by H+ when it is beyond the downstream distance of 0.75 RM (RM is Mars’ radius), where the occurrence rate of current sheets with dominant H+ (heavy ions) weakly increases (decreases) with solar wind density and dynamic pressure.

The plasma environment of Mars is highly influenced by crustal remnant magnetism in the planet. In this work, we do statistical analyses of MAVEN and MGS data to study whether the ionospheric plasma flow can move crustal magnetic field lines, by advection. Due to the day-tonight flow of the plasma, the magnetic field lines are expected to be dragged away in anti-solar direction, causing a shift between observed and modeled field. The results show that a small shift can be observed above weak anomalies on the Northern hemisphere, where the ionospheric plasma flow is less perturbed by strong magnetic fields. To investigate the relative forces between the moving plasma and the crustal field, we also calculated dynamic, magnetic and thermal pressures, since they are involved in the advection process. In general, the dynamic pressure is lower than the other two, but this does not mean advection cannot occur, because the process is not simply a pressure balance, but a diffusive process. The calculation shows that, if advection occurs on Mars, the speed at which the crustal field lines are displaced is much smaller than the speed of the ionospheric plasma flow.