Abstract. During the first Earth gravity assist maneuver of JUICE on 20th August 2024 the spacecraft passed through the Earth plasmasphere for about 2 hours. Before closest approach at a distance of 2.1 RE the Jovian Electron and Ion spectrometer JEI of the PEP instrument suite was switched on for 40 min in an ion mode test configuration. The high plasma density of about 3000/cm3 (observed by the RPWI plasma wave instrument) led to a negative charging of the spacecraft which allowed a rare observation of the cold and dense plasmaspheric ion populations. Since the ions are only corotating with the Earth at a velocity of about 1 km/s at this distance the observed ion speed is dominated by the spacecraft velocity of about 8 km/s. For this reason ions with different mass appear at different energies in the energy spectrum observed by the JEI sensor. In addition the spacecraft potential leads to specific filtering of ion masses in the observed angular distribution. By calculating the sensor response function for these specific observing conditions it is possible to quantify densities of the different ion species. But this response calculation depends critically on the response of the JEI channel electron multipliers to the ion velocity and mass. Since the sensor was operated with a low post-acceleration further laboratory calibrations may be needed for this specific setup. Still we can already conclude from the observations that ions with mass >4 amu/q contribute at least 30 % to the observed total ion density. A flux peak observed in the energy spectrum at 15 eV can only be explained by the presence of heavy molecular ions with mass ~30 amu/q. Molecular ions have only been rarely detected in the outer Earth plasmasphere. The observations indicate that the JEI sensor can also be used to achieve ion composition measurements in the exospheres of the Jovian moons.

We investigate Mercury's response to rare, low Alfvénic Mach number solar wind conditions using observations from the Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) mission. This study provides compelling evidence of Mercury's altered magnetospheric state under these extreme conditions, including the first observational confirmation of Alfvén wing formation at the planet. Our analysis estimates that the upstream conditions during the interplanetary coronal mass ejection (ICME) were sub‐to trans‐Alfvénic ( 1.5). These unusually low solar wind conditions were driven by large interplanetary magnetic fields (IMF) associated with an ICME impact observed by MESSENGER on 30 December 2011. During this 17 hr event, MESSENGER completed one orbital pass through Mercury's magnetosphere, capturing magnetic field and plasma observations of its altered state. We compare these observations to a three‐dimensional magnetohydrodynamic simulation of the event and to MESSENGER observations under typical conditions ( 5.0). Compared with its nominal state, the dayside magnetosphere during the ICME exhibited a weaker, more expanded bow shock and significantly lower plasma density within the magnetosheath. On the nightside, MESSENGER observed a highly inclined magnetic field relative to the typical magnetospheric magnetic field, populated with high‐density plasma consistent with the formation of an Alfvén wing– a characteristic feature of sub‐Alfvénic magnetospheric interactions. This investigation of Mercury under extreme conditions provides insights into the nominal, sub‐Alfvénic interactions between many outer planet moons and their host planet's magnetosphere and also informs our understanding of the many exoplanetary‐stellar wind interactions occurring in low‐ environments.

We investigate energetic proton depletions during Europa flybys E17 and E25A* by the Galileo mission. Energetic ion observations along trajectories like those of E17 & E25A are suitable for isolating the characteristics of the global configuration of the interaction region of Europa (or any Galilean moon) with the Jovian magnetosphere. Both of these flybys passed through Europa’s Alfvén wings further away from the moon, where ionospheric effects are small.We simulate the measured flux with a Monte Carlo particle tracing code and investigate the effect of the following factors: inhomogeneous electromagnetic fields, Europa's induced dipole, atmospheric charge exchange and plumes.We find that the homogeneous fields do not explain the Galileo data. We propose that the perturbed fields associated with the Alfvén wings affect the proton depletions. The inhomogeneous fields and induced dipole alter the pitch angle distribution of the depletion along the trajectory. The plumes that are investigated in this study have a minor effect on the proton depletions compared to the inhomogeneous fields and Alfvén wings. The contribution of atmospheric charge exchange to the depletion is negligible for these flybys. Finally, we compare the simulations to the measured proton flux and discuss the contribution of the effects we have considered.* E25A is a segment of the Io flyby I25

We use Spacecraft Plasma Interaction Software (SPIS) simulations of the surface charging of the Jupiter Icy Moons Explorer (JUICE) spacecraft to study how the variable magnetospheric environment of Jupiter will impact the future JUICE particle and electric field measurements. The study has been limited to the magnetospheric region relevant for JUICE, that is, the environments of the inner and middle magnetosphere of Jupiter. The closest approach of Jupiter will be at 9.3 RJ. In the inner magnetosphere the spacecraft will charge a few volts negative for the typical plasma sheet environment, where ne,cold ≈ 50 cm-3 and Te,cold ≈ 20 eV. However, Galileo detected plasma densities of up to 600 cm-3 in the region around 9.4 RJ (Kurth et al., 2001). These densities could be due to activity on Europa, such as plumes, or a local disturbance of cold and dense iogenic plasma (Bagenal et al., 2015). Such high densities could result in surface potentials of tens of volts, when assuming Te,cold ≈ 5 eV, which would inhibit cold electron measurements performed by the electron spectrometer of JUICE, since the electrons would be repelled before reaching the detector. In addition, the large differential charging of tens of volts, due to the dielectric surfaces, would disturb electric field measurements. However, the cold electron temperature is not well constrained for this particular disturbance and a lower plasma temperatures would decrease the magnitude of the surface potential. Our SPIS simulations show surface potentials of a few volts positive for typical magnetospheric environments in the plasma sheet between 15 and 26 RJ, where ne,cold > 20 ne,hot and the hot electron component range from 1-5 keV. However, Galileo measurements occasionally show hot electron densities equal to or slightly larger than the typical cold electron densities (Futaana et al., 2018). Simulated surface potentials, using ne,cold ≈ ne,hot, show no significant difference compared to the typical environment since the increase in hot electrons is counterbalanced by the increase in the production of secondary electrons. In this particular environment, higher electron densities will charge the spacecraft more negative while higher secondary electron production will charge the spacecraft more positive. Assuming Maxwellian distributions, we obtain that an unusually dense hot, 1-5 keV, electron component, like the one measured by Galileo, would not disturb the particle measurements of JUICE. Our study shows that the absolute charging of the spacecraft strongly depends on the cold electron density and temperature, and, for certain environments, on the spacecraft orientation relative to the plasma flow and the solar radiation. An unusually dense and hot, 1-5 keV, electron plasma component will not have a substantial impact on the charging, in the studied region. We are investigating whether different energy distributons will change this conclusion. The SPIS JUICE surface charging simulation results show that only minor perturbations will be obtained in typical Jovian magnetospheric environments, while substantial perturbations will occasionally occur in the disturbed magnetosphere.

The magnetotail lobe region at Mercury is characterized by low plasma density and low magnetic field variability compared to the nightside magnetosheath and central plasma sheet. At Mercury, as well as other planets, lobe magnetic fields play a crucial role in storing and releasing magnetic flux in response to changing upstream solar wind conditions such as interplanetary magnetic field (IMF) orientation and solar wind dynamic pressure (P-dyn). This makes the region significant for studying the magnetospheric interaction with the intense solar wind conditions at Mercury's orbit. Here, we identify and analyze magnetotail lobe observations made by the Mercury Surface, Space Environment, Geochemistry and Ranging (MESSENGER) spacecraft during its 4 years orbital phase. We empirically determined a set of criteria using magnetometer (MAG) and the Fast Imaging Plasma Spectrometer instruments onboard MESSENGER to identify lobe magnetic field intervals. From 3,332 MESSENGER orbits, we identify 1,242 lobe field intervals. We derive an expression for the average lobe magnetic field strength in nanotesla with respect to radial distance downtail: B-lobe(r) = (135 +/- 8) * r((-2.1 +/- 0.3)) + (31 +/- 8). The lobe magnetic field exhibits both small-scale (similar to 3 min) and orbit-to-orbit (similar to 8-12 hr) variability in magnetic field strength compared to this averaged field strength expression. The orbit-to-orbit variability in lobe field strength is not significantly correlated with estimated IMF orientation, but is directly correlated with P-dyn. Thus, our findings provide evidence for the pressure balance between the inward facing P-dyn on the nightside magnetopause and the outward facing magnetic pressure supplied by the lobes.

With the begining of Juice’s cruise phase, the first datasets of the nominal mission are expected in 2031. A need for an integrated and user-friendly data environment to support the research community and their analysis efforts was identified a few years ago. In response to this demand, we have purposefully crafted an expansive data environment tailored explicitly for the Juice mission. This environment is designed to streamline and enhance the research process by offering researchers a centralized platform containing a wealth of information. Our platform complements the PSA by enabling access to project auxiliary data, as inferred from the document management system, a living archive of project documentation, and access to mission tools. In more detail, it encompasses information regarding details about the spacecraft itself, such as trajectory, instrumentation, and 3D models. Moreover, it provides technical data and specifications necessary for researchers to effectively interpret the mission’s observations. It also houses valuable information on the scientific aspects of the Juice mission, such as workshop presentations, the latest published papers, or relevant databases. By providing comprehensive, easily accessible information, we aim to empower researchers within the scientific community to conduct in-depth analysis and gain valuable insights from the wealth of data generated by the Juice mission.

This article presents the first study of the interaction between the Jupiter Icy Moons Explorer (JUICE) spacecraft and the solar wind environment at 1 AU. The state-of-the-art software Spacecraft Plasma Interaction Software was used to simulate the surface charging of the spacecraft and the altered particle environment around the spacecraft. The simulations show that for a typical solar wind environment the spacecraft will charge to around 6 V, with the different dielectric parts of the spacecraft charging to potentials from around -36 to 8 V. For the studied extreme solar wind environment, similar to the environment found in the sheath region inside the shock front of an Interplanetary Coronal Mass Ejection, the surface potential of the spacecraft is lower due to the increased accumulation of electrons. The spacecraft will charge to around 3 V, with the different dielectric surfaces charging from around -45 to 9 V. We also show how the interaction between the spacecraft and its environment alters the ion and electron particle environment around the spacecraft. This study is the first step toward developing correction techniques for the impact that the interaction between the JUICE spacecraft and its environment has on the JUICE charged particle and field measurements. All spacecraft interact with their space environment. This interaction can create a variety of different problems, with a severity that depends on the environment and the design of the spacecraft. Here, we present a study of the interaction between the Jupiter Icy Moons Explorer (JUICE) spacecraft and the solar wind environment at 1 AU. We study both a typical solar wind environment and an extreme environment, for example, the environment encountered during an Interplanetary Coronal Mass Ejection. Our simulations show that we can expect the different parts of the spacecraft to charge from around -45 to 9 V. The interaction between JUICE and the solar wind will also alter the particle environment around the spacecraft. We present the altered charged particle environment around the spacecraft, both for the ion and the various electron populations. This study is the first step toward developing correction techniques for the impact that the interaction between the JUICE spacecraft and its environment has on the JUICE measurements. The interaction between the Jupiter Icy Moons Explorer spacecraft and the solar wind environment at 1 AU, is simulated We present the spacecraft surface potentials, typically ranging from -45 to 9 V, for different solar wind conditions We also present the near spacecraft particle environment, which is altered due to the interaction between the spacecraft and its environment

The flux of energetic protons (80 keV-1.04 MeV) near the Galilean moons was measured by the Energetic Particle Detector (EPD) on the Galileo mission (1995 - 2003). Near Galilean moons (such as Io and Europa) depletions of the energetic ion flux, of several orders of magnitude, were observed (see Figure 1).Such energetic ion depletions can be caused by the precipitation of these particles onto the moon’s surface or charge exchange with the neutral atmosphere. In addition, a magnetic field gradient can restrict access of the ions to certain regions, creating a “forbidden region.” To interpret the depletion features in the EPD data, a Monte Carlo particle tracing code has been developed. The expected flux of the energetic ions is simulated under different scenarios including those with and without an atmosphere, plume or inhomogeneous electromagnetic field. By comparing the simulated distribution to the EPD data, the cause of the depletion features can be investigated. We identify the following causes of energetic proton depletions near Europa:Depletions are consistent with plumes during the flybys E12 and E26. These plumes coincide with the source location of Jia et al., 2018 and Arnold et al., 2019. Depletions are consistent with atmospheric charge exchange during the flyby E26 Depletions coincide with Europa’s Alfvén wing during the flybys E17 and E25A. The Alfvén wings are two cylindrical regions extending to the north and south of Europa in which the low-energy plasma and the magnetic field are modified compared to the upstream conditions. Furthermore, we investigate the effect of varying the atmospheric properties (scale height, density, presence of a sputtered component) and plume properties (density, location) on the depletions. Figure 1: Normalized flux of H+ (220 to 550 keV) during the Galileo flybys of Europa. Depletions shown as darker colors.

Ganymede is the only moon in our Solar System known to have its own global magnetic field, which generates a miniature moon magnetosphere inside the Jovian magnetosphere. Due to this unique characteristic of Ganymede, its auroral zone is also of particular scientific interest, as it is the only known example of this specific kind of interaction. The JUICE spacecraft will orbit Ganymede for almost a year, with a high inclination orbit with multiple auroral zone crossings. JUICE will study the auroral zone of Ganymede in more detail than ever before, providing both in-situ and remote sensing observations.In this work, we use Spacecraft Plasma Interaction Software (SPIS) simulations to study the spacecraft charging of JUICE in the auroral zone. Hubble Space Telescope observations of the aurora of Ganymede show localized regions of bright spots superimposed on a continuous background emission (e.g. Feldman et al. 2000, Eviatar et al. 2001). In order to produce bright auroras, the electron population needs to be accelerated up to hundreds of eV (Eviatar et al. 2001). Preliminary simulation results, using an auroral electron population with temperature Te = 200 eV and density ne = 300 cm-3, shows frame charging (i.e. spacecraft ground) of around 10 V and differential charging of around 30 V. High frame and differential potentials can cause disturbances in both particle and electric field measurements and prevent accurate characterization of the environment. Since the auroral zone of Ganymede is of particular scientific interest, it is important to study and prepare for this kind of disturbances. ReferencesD. Feldman et al., HST/STIS ultraviolet imaging of polar aurora on Ganymede, The Astrophysical Journal, 535(2), 2000A. Eviatar et al., Excitation of the Ganymede ultraviolet aurora, The Astrophysical Journal, 555(2), 2

We investigate the causes of energetic proton (80–540 keV) depletions measured during the two most distant flybys of Europa by Galileo, E17 and E25A, which encountered the Alfvén wings. First, by simulating the proton flux with a Monte Carlo particle tracing code we investigate the effect of: electromagnetic field perturbations, the induced dipole, atmospheric charge exchange and plumes. Inhomogeneous fields associated with the Alfvén wings and the ionosphere strongly affect the depletions. For homogeneous fields the depletion along the trajectory is focused on a narrow pitch angle range and has no structure, whereas the depletion for perturbed (inhomogeneous) fields represents a wider and complex structure. Furthermore, also the induced dipole alters the depletion structure. The effect of plumes (density 2.5 × 10 15 m −3 ) and charge exchange on the proton depletion is minor. Second, we compare the simulations to the proton measurements. The simulations with inhomogeneous fields describe the data qualitatively better than the homogeneous case, suggesting that indeed field perturbations are responsible for the measured losses. We attribute discrepancies between the simulations and the proton measurements to discrepancies between the simulated and real fields. We argue that simulating the fields along the trajectory is a good first step, but that ideally the energetic ion flux is reconstructed well to gain confidence in the interpretation of the simulated magnetic field. In conclusion, energetic ion observations along distant flybys through the Alfvén wings are suitable for isolating the characteristics of the global configuration of the magnetospheric interaction region of Europa (or other moons).

Spacecraft charging is a well‐known effect that occurs when a spacecraft is located in a charged environment such as plasma. In this process, the surface of the spacecraft acquires an electrostatic potential through the accumulation and emission of positive and negative charges. In addition to causing severe electrostatic discharges, it also significantly affects low‐energy particle measurements performed by instruments onboard the spacecraft as it causes a change in energy and a distortion of the Field Of View (FOV) of the instrument by modifying the trajectory of measured particles. Spacecraft charging is therefore an important aspect to consider for Jovian plasma Dynamics and Composition analyzer (JDC), an instrument which aims to perform cold plasma measurements around the Galilean moons onboard JUpiter ICy moons Explorer (JUICE). In this study we use SPIS to perform simulations to study the FOV distortion of JDC for positive ions caused by spacecraft charging in two environments of the JUICE mission: the ionosphere of Ganymede and the Jovian magnetosphere. We show that the resulting distortion of the instrument FOV is highly space dependent and varies in shape and intensity from a pixel to another. However, we show that in both environments the complexity of the interactions between measured positive ions and the spacecraft can be decomposed and described as a superposition of a finite number of elementary interactions (i.e., modes). We show that each mode is caused by a specific element of the spacecraft and leads to a characteristic distortion of the instrument FOV. This study constitutes a first step toward necessary spacecraft potential corrections of the measurements performed by JDC.

We study the effect of negatively charged dust on the magnetic-field-aligned polarisation electrostatic field ($\boldsymbol {E}_{\parallel }$) using Cassini's RPWS/LP in situ measurements during the ‘ring-grazing’ orbits. We derive a general expression for $\boldsymbol {E}_{\parallel }$ and estimate for the first time in situ $\lVert \boldsymbol {E}_{\parallel } \rVert$ (approximately $10^{-5} \, \text {V}\, \text {m}^{-1}$) near the Janus and Epimetheus rings. We further demonstrate that the presence of the negatively charged dust close to the ring plane ($\vert \text {Z} \vert \lesssim 0.11 \, \text {R}_{s}$) amplifies $\lVert \boldsymbol {E}_{\parallel } \rVert$ by at least one order of magnitude and reverses its direction due to the effect of the charged dust gravitational and inertial forces. Such reversal confines the electrons at the magnetic equator within the dusty region, around $0.047 \, \text {R}_{s}$ above the ring plane. Furthermore, we discuss the role of the collision terms, in particular the ion–dust drag force, in amplifying $\boldsymbol {E}_{\parallel }$. These results imply that the charged dust, as small as nanometres in size, can have a significant influence on the plasma transport, in particular ambipolar diffusion along the magnetic field lines, and so their presence must be taken into account when studying such dynamical processes.

Jupiter Icy Moons Explorer (JUICE) is the first European space mission for the exploration of the Jupiter system including the Galilean moons Callisto, Europa, and Ganymede. In order to enable maximum science return of the in-situ electric field and particle measurement instruments, the control of surface charging of the spacecraft in the Jovian plasma environment plays an essential role. In this paper, the various challenges and design choices that have been made for the sake of surface charging control of the JUICE satellite are described. The results of detailed 3D charging simulations performed for the final verification of the impact on the concerned experiments are presented and discussed.

JUICE is ESA’s first large class mission to the outer Solar System. The main objectives of JUICE are to study Jupiter and its space environment with a special focus on Jupiter’s moons Europa, Ganymede, and Callisto, and their potential habitability. In order to fulfil these objectives, the JUICE measurements need to be accurately corrected for any possible perturbations. Here, we present Spacecraft Plasma Interaction Software (SPIS) simulations of the surface charging of JUICE in the solar wind. The results will be used to correct the future JUICE measurements for the impact of the charging. We have used a solar wind environment model (i.e. a description of the environment covering typical values for parameters such as electron and ion densities, temperatures, and velocities, magnetic field strengths, and EUV flux) for the location where JUICE will perform its first measurements, between 1500 and 3000 RE from Earth. The typical values for the solar wind parameters and the minimum and maximum values from the expected parameter ranges have been used to simulate the interaction in both average and “extreme” solar wind conditions. Here we present the main results from the SPIS simulations: the surface potential of the spacecraft; the potentials at the locations of the particle and field instrumentation such as the RPWI Langmuir probes and the PEP plasma analysers; the electron and ion density at the locations of the RPWI instruments and the PEP plasma analysers; the characteristics of perturbing particle populations such as photoelectron and secondary electron populations produced by the spacecraft itself; and the properties of the ion wake of the spacecraft. The detailed knowledge of the listed parameters will be used to provide accurate analyses of the first in-situ particle and field measurements performed by JUICE.

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We have characterized spacecraft charging events in low Earth orbit (LEO) polar regions with the Active Monitor Box of Electrostatic Risk (AMBER) instrument onboard the Joint Altimetry Satellite Oceanography Network—3 (Jason-3) ocean topography mission for the first time for this spacecraft. AMBER data, taken at an altitude of 1336 km, over the period January 2017–March 2020, with measurements recorded close to the current solar minimum have been analyzed, using systematic filtering of ions spectrograms with selected threshold energies and time windows to detect negative spacecraft charging events; 109 spacecraft charging events were found. The events are examined visually and characterized by their spatial and temporal location, duration, and intensity (e.g., spacecraft potential). At the Jason-3 altitude (1336 km), the ion signature predominately lasts under 30 s in conjunction with auroral inverted V crossings, while intense fluxes of electrons corresponding to the encounter of the discrete auroral region last between 30 s and 1 min. Most of the detected spacecraft charging events show charging levels between −30 and −1000 V. The spacecraft charging events are located in the magnetic local time (MLT) sector 17h–05h, predominately before midnight. The distribution is equal between the northern and southern hemispheres. We found a high correlation between the charging time profile and that of the auroral electron average energy and energy flux along the satellite path. Overall statistics over three years as well as different event morphologies, electron spectra, and comparisons to worst case electron flux spectral distributions are presented and discussed.

The possible presence of life in the atmosphere of Venus has been debated frequently over the last 60 years. The discussion was recently reignited by the possible detection of phosphine (PH3), but several other chemicals potentially relevant for life processes are also found in the middle atmosphere. Moreover, the reasons for the heterogeneous ultraviolet (UV) absorption between 320 and 400 nm in the altitude range ∼40–70 km are still not well understood. These aspects could be further studied in-situ by UV Raman and fluorescence instruments. Here, the conceptual design of a small balloon probe (<20 kg) is presented, including a science payload comprising a UV laser, spectrometer, and a telescope. The goal of the proposed mission is to analyse the absorption of UV light in Venus’ atmosphere, to study the atmospheric composition, and to verify the possible presence of biomarkers. Current state-of-the-art technologies would allow a more cost-efficient and easy to develop mission, as compared to previous Venus probes. This article is focused on the scientific instrumentation, as well as on the mass and power budgets required to realise the proposed mission.

The objective of this White Paper, submitted to ESA's Voyage 2050 call, is to get a more holistic knowledge of the dynamics of the Martian plasma system, from its surface up to the undisturbed solar wind outside of the induced magnetosphere. This can only be achieved with coordinated multi-point observations with high temporal resolution as they have the scientific potential to track the whole dynamics of the system (from small to large scales), and they constitute the next generation of the exploration of Mars analogous to what happened at Earth a few decades ago. This White Paper discusses the key science questions that are still open at Mars and how they could be addressed with coordinated multipoint missions. The main science questions are: (i) How does solar wind driving impact the dynamics of the magnetosphere and ionosphere? (ii) What is the structure and nature of the tail of Mars' magnetosphere at all scales? (iii) How does the lower atmosphere couple to the upper atmosphere? (iv) Why should we have a permanent in-situ Space Weather monitor at Mars? Each science question is devoted to a specific plasma region, and includes several specific scientific objectives to study in the coming decades. In addition, two mission concepts are also proposed based on coordinated multi-point science from a constellation of orbiting and ground-based platforms, which focus on understanding and solving the current science gaps.

Some of the major discoveries of the recent Cassini-Huygens mission have put Titan and Enceladus firmly on the Solar System map. The mission has revolutionised our view of Solar System satellites, arguably matching their scientific importance with that of their host planet. While Cassini-Huygens has made big surprises in revealing Titan's organically rich environment and Enceladus' cryovolcanism, the mission's success naturally leads us to further probe these findings. We advocate the acknowledgement of Titan and Enceladus science as highly relevant to ESA's long-term roadmap, as logical follow-on to Cassini-Huygens. In this White Paper, we will outline important science questions regarding these satellites and identify the science themes we recommend ESA cover during the Voyage 2050 planning cycle. Addressing these science themes would make major advancements to the present knowledge we have about the Solar System, its formation, evolution, and likelihood that other habitable environments exist outside the Earth's biosphere.