Jan-Erik Wahlund

Mercury's magnetosphere is an extremely dynamic environment, where substorm‐like activity, including dipolarization fronts and particle acceleration, periodically disrupts the stability and radial extent of the closed field line region. The common narrowband ∼1 Hz waves at Mercury, near the local proton gyrofrequency are preferentially observed on closed field lines during quieter intervals, but their relationship to magnetospheric dynamics remains poorly understood. Here, we combine MESSENGER data sets of ∼1 Hz wave activity and dipolarization fronts to investigate whether newly closed field lines can sustain wave growth. We find that ∼1 Hz waves on the nightside are systematically absent during orbits with dipolarization intervals and typically confined within 1.3 R _M , compared to greater downtail extents during quiet intervals. The results indicate that ∼1 Hz waves require long‐lived, stable closed field lines to grow; therefore, when they are observed, they can serve as diagnostics of Mercury's magnetospheric state, establishing a clear connection between field‐line history, magnetospheric dynamics, and wave occurrence in Mercury's magnetotail.

The JUICE spacecraft performed an Earth gravity assist during the 20-21st August 2024 encountering a range of different plasma environments. An understanding of the surface charging of the spacecraft is important in increasing the scientific output of the instruments, allowing for the development of correction techniques. The surface charging in two of these environments, in the plasmasphere at closest approach (2.07 RE) and in the magnetosheath, was explored through simulations using the SPIS software. The average surface charging of the conductive surface was found to charge negatively in the plasmasphere to -2 V and positively in the magnetosheath to 2.5 V. Differential charging was observed in both environments due to different materials covering the spacecraft, with the dielectric materials charging from -0.8 to -6 V in the plasmasphere and 7 to -70 V in the magnetosheath. The effect of the spacecraft on the particle environment was also studied, looking at the formation of ion wakes and the photoelectron cloud. In the plasmasphere, the impact of exposed potentials on the solar array was also studied and found not to have any significant effect on the overall charging of the spacecraft. The results obtained here during the Earth swing-by can also be applied when JUICE performs later gravity-assists again at the Earth and the results will be relevant when encountering similar environments at Jupiter and its moons.

The JUICE spacecraft performed an Earth gravity assist during the 20-21st August 2024 encountering a range of different plasma environments. An understanding of the surface charging of the spacecraft is important in increasing the scientific output of the instruments, allowing for the development of correction techniques. The surface charging in two of these environments, in the plasmasphere at closest approach (2.07 RE) and in the magnetosheath, was explored through simulations using the SPIS software. The average surface charging of the conductive surface was found to charge negatively in the plasmasphere to -2 V and positively in the magnetosheath to 2.5 V. Differential charging was observed in both environments due to different materials covering the spacecraft, with the dielectric materials charging from -0.8 to -6 V in the plasmasphere and 7 to -70 V in the magnetosheath. The effect of the spacecraft on the particle environment was also studied, looking at the formation of ion wakes and the photoelectron cloud. In the plasmasphere, the impact of exposed potentials on the solar array was also studied and found not to have any significant effect on the overall charging of the spacecraft. The results obtained here during the Earth swing-by can also be applied when JUICE performs later gravity-assists again at the Earth and the results will be relevant when encountering similar environments at Jupiter and its moons.

The Cassini Radio & Plasma Wave Science (RPWS) and Ion and Neutral Mass Spectrometer (INMS) observations of Saturn’s ionosphere during the proximal orbits (Rev) 288 – 293 in the altitude range 1450 – 2500 km (above the 1-bar pressure level) are modelled with the inclusion of a dust component. Previous reports have revealed that large amounts of nm- to mm-sized dust grains precipitate from the D-ring into the atmosphere of Saturn’s equatorial region. We find that the processed charged dust (< 2 nm radius) has a profound effect on the ionospheric structure, enhancing the ion number density well above photochemical equilibrium levels, while the free electrons tend to become attached to the dust population as a result of a low photo-electron detachment rate by EUV light from the Sun at the distance of Saturn. The charged dust layers are influenced by the strong near horizontal magnetic field inhibiting vertical ambipolar diffusion as most charged components are magnetized above about 1800 km. Our dust-ionosphere model calculations reveal that layers of mostly singly negatively charged dust can explain much of the observed ionospheric densities. Modelling uncertainties include sticking coefficients, recombination rates, dust distributions and the presence of negative ions as well as variations thereof along the spacecraft trajectory. Our models generate overall acceptable fits to the observed RPWS electron and ion densities. The observations are therefore compatible with charged grains (and/or cluster ions) being present and playing a dominant role in the Kronian ionosphere structure and chemistry. Similar processes may be active at gas giants with associated ring systems.

The JUICE spacecraft performed an Earth gravity assist during the 20-21st August 2024 encountering a range of different plasma environments. An understanding of the surface charging of the spacecraft is important in increasing the scientific output of the instruments, allowing for the development of correction techniques. The surface charging in two of these environments, in the plasmasphere at closest approach (2.07 RE) and in the magnetosheath, was explored through simulations using the SPIS software. The average surface charging of the conductive surface was found to charge negatively in the plasmasphere to -2 V and positively in the magnetosheath to 2.5 V. Differential charging was observed in both environments due to different materials covering the spacecraft, with the dielectric materials charging from -0.8 to -6 V in the plasmasphere and 7 to -70 V in the magnetosheath. The effect of the spacecraft on the particle environment was also studied, looking at the formation of ion wakes and the photoelectron cloud. In the plasmasphere, the impact of exposed potentials on the solar array was also studied and found not to have any significant effect on the overall charging of the spacecraft. The results obtained here during the Earth swing-by can also be applied when JUICE performs later gravity-assists again at the Earth and the results will be relevant when encountering similar environments at Jupiter and its moons.

The JUICE spacecraft performed an Earth gravity assist during the 20-21st August 2024 encountering a range of different plasma environments. An understanding of the surface charging of the spacecraft is important in increasing the scientific output of the instruments, allowing for the development of correction techniques. The surface charging in two of these environments, in the plasmasphere at closest approach (2.07 RE) and in the magnetosheath, was explored through simulations using the SPIS software. The average surface charging of the conductive surface was found to charge negatively in the plasmasphere to -2 V and positively in the magnetosheath to 2.5 V. Differential charging was observed in both environments due to different materials covering the spacecraft, with the dielectric materials charging from -0.8 to -6 V in the plasmasphere and 7 to -70 V in the magnetosheath. The effect of the spacecraft on the particle environment was also studied, looking at the formation of ion wakes and the photoelectron cloud. In the plasmasphere, the impact of exposed potentials on the solar array was also studied and found not to have any significant effect on the overall charging of the spacecraft. The results obtained here during the Earth swing-by can also be applied when JUICE performs later gravity-assists again at the Earth and the results will be relevant when encountering similar environments at Jupiter and its moons.

In this study, we combine Cassini fields and particle observations to investigate Titan's induced magnetosphere from the TA to T82 flybys, including flybys from the Cassini prime, equinox, and part of the solstice mission, to investigate the average location and the shape of Titan's induced magnetosphere. Although earlier studies have provided valuable information on Titan's induced magnetosphere, they were largely based on separate analyses of fields and particle data. We provide an integrated map of electron density and temperature in Titan's near plasma environment to outline the external boundary of the induced magnetosphere. We identify a dense ionospheric region and an extended plasma wake with electron densities ranging between and c. In addition, we systematize the spatial distribution of pick‐up ions at Titan with respect to the background convective electric field. We indicate that pickup ions are found in the positive hemisphere of the Kronian plasma convective electric field. The mass of the observed pickup corresponds to methane group ions, ions as well as protons and molecular hydrogen ions. The Kronian background electric field progressively accelerates these ions, and we estimate its intensity by reconstructing the radial energy gain of this population in response to the convective electric field. We find the estimated from the pickup ions electric field values within 0.05 mV and 1.92 mV range, which is consistent with an estimate of 0.61 mV deduced from computation.

The JUICE spacecraft performed an Earth gravity assist during the 20-21st August 2024 encountering a range of different plasma environments. An understanding of the surface charging of the spacecraft is important in increasing the scientific output of the instruments, allowing for the development of correction techniques. The surface charging in two of these environments, in the plasmasphere at closest approach (2.07 RE) and in the magnetosheath, was explored through simulations using the SPIS software. The average surface charging of the conductive surface was found to charge negatively in the plasmasphere to -2 V and positively in the magnetosheath to 2.5 V. Differential charging was observed in both environments due to different materials covering the spacecraft, with the dielectric materials charging from -0.8 to -6 V in the plasmasphere and 7 to -70 V in the magnetosheath. The effect of the spacecraft on the particle environment was also studied, looking at the formation of ion wakes and the photoelectron cloud. In the plasmasphere, the impact of exposed potentials on the solar array was also studied and found not to have any significant effect on the overall charging of the spacecraft. The results obtained here during the Earth swing-by can also be applied when JUICE performs later gravity-assists again at the Earth and the results will be relevant when encountering similar environments at Jupiter and its moons.

We use Spacecraft Plasma Interaction Software (SPIS) simulations to study surface charging of and outgassing from the Jupiter Icy Moons Explorer (JUICE) spacecraft during the JUICE lunar gravity assist (LGA). The results of this study will be of great importance for future observations of the plasma environments of Jupiter and its icy moons.On August 19, 2024, JUICE performed its first gravity assist maneuver at the Moon, which was located in Earth’s south magnetotail lobe region. During LGA, the two ARTEMIS spacecraft, P1 and P2, were orbiting the Moon. Despite being separated by approximately 14,000 km, the ARTEMIS P1 and P2 observations of the magnetic field and plasma parameters (density, velocity, and temperature) are in excellent agreement. As JUICE was only 4,000 to 7,000 km from ARTEMIS P2, these observations are considered representative of the space environment encountered by JUICE during the LGA. The ARTEMIS P1 and P2 observations are therefore used as input for the surface charging and outgassing simulations.SPIS is used to simulate the interaction between the JUICE spacecraft and its environment during the LGA (excluding the lunar wake crossing). Our simulation results show that the spacecraft bus reaches a potential of approximately 11 V, while non-conductive surfaces, such as the radiators and the high-gain antenna, reach potentials ranging from - 2 to 14 V. These surface potentials affect both cold plasma and electric field measurements. Due to the tenuous plasma environment in the magnetotail lobe and the spacecraft being located at 1 AU, hence relatively close to the Sun, the surface charging is predominantly driven by the emission of photoelectrons from the spacecraft. During LGA, shortly after JUICE crossed the lunar terminator, a suspected outgassing event occurred. Several independent JUICE observations are consistent with an outgassing event, including the detection of water molecules moving away from the spacecraft, a sudden increase in the local plasma density accompanied by a decrease in the spacecraft potential, and an unforeseen excess torque acting on the spacecraft. SPIS is also used to simulate the suspected outgassing event and to assess its impact on the spacecraft charging and the JUICE particle and field measurements.