In 2031 the JUICE spacecraft will perform a multi-flyby tour of the Jovian system. Next to the radiometric tracking that is performed for navigation operations, the dedicated radio science instrument (3GM) collects high-accuracy radiometric measurements during the flybys. We investigate the capability of the radio science data to provide improved moon state knowledge during navigational operations. We introduce ephemeris updates from radio science data into our simulated navigation operations and examine the potential savings of statistical ΔV for corrective manoeuvres. A navigation orbit determination (OD) solution was simulated for the multi-flyby tour of JUICE, including the resulting state knowledge evolution of the Galilean moons. The OD was extended by an interface for external moon ephemeris updates, which was used to evaluate the impact of radio science generated external ephemerides on the statistical ΔV budgets for post-flyby cleanup manoeuvres. The moon state knowledge evolution during navigation operation showed a rapid reduction of the a-priori moon state uncertainty, for which the navigational tracking data coverage of the long, early tour arcs was identified as the driving factor. As a result of the longer tracking arcs, the moon state knowledge from navigation data results improves more quickly during the initial phase of the tour. Since the impact of moon state knowledge on the corrective manoeuvres is largest in this initial phase, the comparative analysis of the statistical ΔV cost shows that the adoption of radio science ephemeris products does not effectuate significant ΔV savings. Instead we showed that in order to achieve substantial ΔV savings improvements of Europa's and Ganymede's ephemerides are required ahead of JUICE's arrival. While the analysis concludes that data synergies are unlikely to benefit the navigational operations, it highlights other potential synergies between the navigation and radio science data. A comparatively strong signature of Io's dynamics was found in the simulated navigation data along the long early tour arcs, which could be leveraged for the benefit of the new global moon ephemeris solutions after JUICE.

Since its detection by Mariner 10, helium has been a key focus in studies of Mercury's exosphere. Recently, Weichbold et al. (2025), https://doi.org/10.1029/2024je008679 provided the first in situ helium measurements, inferring density from Ion Cyclotron Wave (ICW) events observed by the MESSENGER spacecraft. This approach enables, for the first time, a helium density profile across a broad altitude range without relying on prior models. We present an ab-initio model for a steady state, solar wind-driven helium exosphere, which informed the interpretation of these ICW measurements. We discuss helium release processes and evaluate whether meteoroid impacts could account for specific instances of elevated helium measurements. We developed a global, semi-analytical model based on a helium-saturated regolith and an average helium source flux of (Formula presented.) He/s from solar wind ion implantation. We calculate the helium flux distribution using an analytical lateral transport model and then generate local radial density profiles from a numerical (Monte Carlo) radial transport model. Additionally, we applied the radial transport model to estimate the scale and duration of large, sporadic helium release events and assess the likelihood of detecting these events in situ. The strong agreement between our model and the novel measurements confirms that the measurable helium exosphere is dominated by thermally recycled particles. We show that elevated helium measurements can result from the vaporization and release of helium from large (1 m) meteoroid impacts, but it is statistically unlikely that more than one impact event is captured in the given set of measurements.