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We develop an analytical model of the Alfvén wings generated by the interaction between a moon's ionosphere and its sub‐Alfvénic magnetospheric environment. Our approach takes into account a realistic representation of the ionospheric Pedersen conductance profile that typically reaches a local minimum above the moon's poles and maximizes along the bundle of magnetospheric field lines tangential to the surface. By solving the equation for the electrostatic potential, we obtain expressions for various quantities characterizing the interaction, such as the number flux and energy deposition of magnetospheric plasma onto the surface, the spatial distribution of currents within the Alfvén wings and associated magnetic field perturbations, as well as the Poynting flux transmitted along the wings. Our major findings are: (a) Deflection of the magnetospheric plasma around the Alfvén wings can reduce the number flux onto the surface by several orders of magnitude. However, the Alfvénic interaction alone does not alter the qualitative shape of the "bullseye"‐like precipitation pattern formed without the plasma interaction. (b) Due to the deflection of the upstream plasma, the energy deposition onto the moon's exosphere achieves its minimum near the ramside apex and maximizes along the flanks of the interaction region. (c) Even when the ionospheric conductance profile is continuous, the currents along the Alfvén wings exhibit several sharp jumps. These discontinuities generate spikes in the magnetic field that are still observable at large distances to the moon. (d) The magnitude and direction of the wing‐aligned currents are determined by the slope of the ionospheric conductance profile. Key Points: We calculate the flow deflection, electric currents, and plasma and energy flux patterns for sub‐Alfvénic moon‐magnetosphere interactionsThe number flux of the magnetospheric flow peaks above the obstacle's ramside apex, but the energy flux achieves its minimum in that regionThe currents along the Alfven wing characteristics exhibit several sharp jumps, generating observable spikes in the magnetic field [ABSTRACT FROM AUTHOR]

This work evaluates the added benefit of using laser altimeter measurements for orbit reconstruction. As a spacecraft orbits a celestial body, its altimetry swaths progressively cross previous swaths. These locations, known as crossover points, yield valuable information about the orbited body and the spacecraft trajectory. The mathematical expressions for the inclusion of crossover measurements into orbit determination algorithms are presented and evaluated. It is shown that a first-order approximation of these expressions is insufficient and a more detailed expression is developed. To evaluate the impact of altimetry crossover measurements on orbit determination, the planetary mission Jupiter Icy moons Explorer (JUICE) by the European Space Agency (ESA) is used as a case study by means of a covariance analysis. In this initial analysis, the assumption is made that all altimetry measurements are obtained with nadir pointing which limits the direct applicability of our method until pointing is accounted for. • Altitude difference crossover measurements improve orbit determination. • Crossovers reduce position uncertainty marginally due to Doppler precision advancements. • Laser altimetry crossovers with JUICE mission as case study. • Covariance analysis of estimation uncertainty when altimetry crossovers are included. [ABSTRACT FROM AUTHOR]

The Ganymede Laser Altimeter (GALA) is one of the ten scientific instruments selected for the Jupiter Icy Moons Explorer (JUICE) mission currently implemented under responsibility of the European Space Agency (ESA). JUICE is scheduled for launch in mid 2022; arrival at Jupiter will be by end of 2029 with the nominal science mission—including close flybys at Ganymede, Europa, and Callisto and a Ganymede orbit phase—ending by mid 2033. GALA's main objective is to obtain topographic data of the icy satellites of Jupiter: Europa, Ganymede, and Callisto. By measuring the diurnal tidal deformation of Ganymede, which crucially depends on the decoupling of the surface ice layer from the deep interior by a liquid water ocean, GALA will obtain evidence for (or against) a subsurface ocean in a 500 km orbit around the satellite and will provide constraints on Ganymede's ice shell thickness. In combination with other instruments, it will characterize the morphology of surface units on Ganymede, Europa, and Callisto providing not only topography but also surface roughness and albedo (at 1064 nm) measurements. GALA is a single-beam laser altimeter operating with up to 50 Hz (nominal 30 Hz) shot frequency at a wavelength of 1064 nm and pulse lengths of 5.5 ± 2.5 ns using a Nd:YAG laser. The return pulse is detected by an Avalanche Photo Diode (APD) with 100 MHz bandwidth and is digitized at a sampling rate of 200 MHz providing range measurements with a subsample resolution of 0.1 m and surface roughness measurements from pulse-shape analysis on the scale of the footprint size of about 50 m at 500 km altitude. The instrument is developed in collaboration of institutes and industry from Germany, Japan, Switzerland, and Spain. [ABSTRACT FROM AUTHOR]

Abstract We examine the dynamics of energetic magnetospheric ions in the highly perturbed and asymmetric electromagnetic environment of the Jovian moon Callisto. The Alfvénic interaction of the (nearly) corotating magnetospheric plasma with Callisto's ionosphere and induced dipole generates electromagnetic field perturbations near the moon, the structure of which vary as a function of Callisto's orbital position. For this study, these perturbations are obtained from the AIKEF hybrid model (kinetic ions, fluid electrons) which has already been successfully applied to Callisto's local plasma environment (Liuzzo et al., 2015, 2016, 2017). To isolate the influence of Callisto's ionosphere and induced dipole field on energetic ion dynamics, we analyze the trajectories of energetic hydrogen, oxygen, and sulfur ions exposed to various configurations of the locally perturbed electromagnetic fields. We present spatially resolved surface maps that display accessibility of Callisto to these ion populations for select energies from 1 keV to 5000 keV. The Alfvénic plasma interaction with (i) Callisto's induced magnetic field, (ii) Callisto's ionosphere, and (iii) the combination of both, all leave distinct imprints in these accessibility patterns. Draping of the magnetospheric field around Callisto's ionosphere partially shields the moon's trailing (ramside) hemisphere from energetic ion impacts, and the induced field tends to focus energetic ion impacts near Callisto's Jupiter-facing and Jupiter-averted apices. Depending on the nature of Callisto's Alfvénic plasma interaction, the accessibility of its surface to energetic protons may evolve non-monotonically with increasing energy. We also present maps of energetic ion accessibility and the resulting energy deposition onto Callisto at the time of the Galileo C3, C9, and C10 flybys. Our findings show that the shielding of Callisto's surface from energetic ion impacts is most effective during flybys that took place while the moon was located at an intermediate distance to the center of Jupiter's magnetospheric current sheet. In this case, the ionosphere and induced dipole field both make substantial contributions to the electromagnetic field perturbations near Callisto. [ABSTRACT FROM AUTHOR]

Using hybrid simulations and analytical calculations, we investigate the observable magnetic perturbations during the 12 planned Callisto flybys of the JUpiter ICy moons Explorer mission. During four of these encounters, Callisto will be embedded within Jupiter's magnetospheric current sheet. In these cases, Callisto's Alfvén wings and ramside magnetic field pileup will partially obscure any magnetic signatures associated with induction in a conducting layer at the moon, thereby severely complicating attempts to further constrain properties of a possible subsurface ocean. During one of these flybys, the plasma interaction will even generate magnetic signatures that are qualitatively similar to an induced field from the moon's interior. In this case, highly accurate measurements of the upstream flow parameters and Callisto's ionosphere are required to disentangle the induction signal from plasma effects. For the remaining eight encounters, Callisto's plasma interaction is expected to be sufficiently weak for an unobstructed observation of the moon's inductive signature. Plain Language Summary: Jupiter's moon Callisto may possess a salty water ocean beneath its icy surface. Due to time variations of Jupiter's magnetic field near Callisto's orbit, electric currents would be induced in such an ocean, generating magnetic field perturbations detectable outside of the moon. Therefore, magnetometer observations near Callisto can be used to prove the existence and constrain the properties of such a subsurface ocean. However, Callisto is also embedded within Jupiter's magnetosphere and is continuously exposed to a flow of plasma particles that rotate synchronously with the planet. The deflection of this plasma around Callisto generates additional electric currents and associated magnetic perturbations that may obscure the induced field from Callisto's interior. Based on modeling of these plasma currents, we demonstrate that during several flybys of the upcoming JUpiter ICy moons Explorer mission, Callisto's induction signal will be buried by plasma effects beyond recognition. These plasma signatures may even look similar to induced fields and may therefore lead to a false positive identification of the ocean. Our work constrains flyby geometries that are suitable to detect water reservoirs beneath the surfaces of Jupiter's icy moons and is highly relevant for the successful planning of synergistic measurements during the JUpiter ICy moons Explorer mission. Key Points: We present a model of Callisto's magnetic environment during the 12 upcoming flybys of the JUICE spacecraftInduction signatures from Callisto's interior will likely be obscured by Alfven wings during several flybysPlasma interaction will generate ambiguities in interpretation of JUICE magnetometer observations [ABSTRACT FROM AUTHOR]

We apply a combination of analytical modeling, hybrid simulations, and data analysis techniques to provide a comprehensive study of magnetometer data from four Galileo flybys of Callisto (C21, C22, C23, and C30) that have never been discussed in the literature before. Callisto's distance to the center of Jupiter's magnetospheric current sheet varied considerably from flyby to flyby. Therefore, the relative strength of the magnetic field perturbations due to Callisto's plasma interaction with Jupiter's magnetosphere and induction within Callisto's subsurface ocean drastically changed as well. During C21, a strong magnetic field perturbation along the corotation direction was detected in Callisto's geometric plasma shadow. This enhancement can be explained with Callisto's steady state plasma interaction only, if the upstream flow possessed a nonnegligible component away from Jupiter. During C22, Galileo only grazed Callisto's Alfvén wings which were elevated out of the flyby plane due to the ambient magnetospheric field orientation. During C23, the combination of an inclined flyby trajectory and finite gyroradius effects caused Callisto's observed Alfvén wings to be slightly asymmetric between both hemispheres. During C30, a discontinuity with a surface normal pointed toward Jupiter was detected within Callisto's geometric plasma shadow, similar to the earlier C10 flyby. Due to strong plasma interaction and an unfavorable flyby geometry (C21), a large closest approach altitude (C22), or weak inducing field (C23 and C30), no discernible induction signatures were observed during these four flybys. Based on data from all available Galileo flybys, we determine requirements on future flyby geometries that must be satisfied for an identification of Callisto's subsurface ocean in magnetometer data. [ABSTRACT FROM AUTHOR]

The JUpiter ICy moons Explorer mission of the European Space Agency, that will be launched in the year 2022, will study the geodesy and physical characteristics of Jupiter and its icy moons Europa, Callisto and Ganymede. The final phase of this mission, planned for the year 2032, is still under investigation and foresees phases in circular orbit around Ganymede. In this paper two types of science orbits around Ganymede, that optimize the observational performances and the probe life-time, are proposed. While the first type allows, at “zero cost”, the obtaining of repeated observations of a given point of the surface, the second type, with a limited cost, adds to the periodicity of observation, the condition of synchronism with the Sun. This synchronism permits both the achievement of a condition of permanent sunlight for the probe, thus leading to an extension of the mission duration, and a minimization of the variations of spectral signature due to the Sun's position. [ABSTRACT FROM AUTHOR]

We designed a tool allowing irradiation of large samples over a surface of A5 size dimension by means of a 2.5 MeV Pelletron electron accelerator. in situ electrical measurements (I-V, conductivity, etc.) can also be performed, in the dark or under illumination, to study radiation effects in materials. Irradiations and electrical measurements are achievable over a temperature range from 100 K to 300 K. The setup was initially developed to test real-size triple junction solar cells at low temperature within the framework of the ESA’s JUICE mission. It will be made available to users at the beginning of 2017. After a brief description of the SIRIUS irradiation facility hosted at Laboratoire des Solides Irradiés (LSI), this paper gives detailed information about the Large Surface Irradiated-Cell (LSIC) device. Preliminary results obtained during the ongoing qualification phase of the setup are also discussed.

Abstract: The JUpiter ICy moons Explorer (JUICE) is an ESA L-class mission concept designed to explore the Galilean satellites of the Jovian system. Although the current mission science goals do not include any astrophysical observations, we find that the planned period of the JUICE mission is optimal for in situ measurements of Interstellar Dust (ISD), due to highly increased flux levels at that time. In case that JUICE carries a dust detector, this could lead to in situ high-resolution mass spectra of ISD grains. Such compositional information on the ISD grains is important for understanding the origins of solar/planetary systems, and therefore could represent a valuable addition to the core JUICE mission science. [Copyright &y& Elsevier]

We examine the dynamics of energetic magnetospheric electrons exposed to the highly perturbed and asymmetric plasma environment of Jupiter's moon Callisto. The interaction of the (nearly) corotating magnetospheric plasma with Callisto's ionosphere and induced dipole locally generates intense electromagnetic pileup and draping signatures which vary as a function of the moon's distance to the center of Jupiter's magnetospheric current sheet. In our study, these field perturbations are represented using output from the AIKEF hybrid (kinetic ions, fluid electrons) model of Callisto's interaction with the corotating plasma. In order to constrain the influence of Callisto's variable electromagnetic environment on the dynamics of energetic electrons, we trace the trajectories of more than 6.7 million test particles as they travel through a distinct configuration of the locally perturbed fields. We present spatially resolved maps that display the accessibility of Callisto to electrons at energies E between 10 1 keV ≤ E ≤ 10 5 keV for multiple sets of these perturbed fields, corresponding to select distances of the moon to the center of the Jovian current sheet. The electromagnetic field perturbations near Callisto play a crucial role in generating inhomogeneous precipitation of energetic electrons onto the top of the moon's atmosphere. In particular, Callisto's Jupiter-facing and Jupiter-averted hemispheres are partially protected from energetic electron precipitation: when located far above or below the center of Jupiter's current sheet, Callisto's induced dipole shields the apices of these hemispheres, whereas near the center of the sheet, strong field line draping protects these regions. In contrast to this, the apex of Callisto's trailing hemisphere is exposed to intense energetic electron precipitation at any distance to the center of the Jovian current sheet. We also present maps of energetic electron accessibility during the Galileo C3, C9, and C10 flybys, and calculate the intensity of energetic electron flux onto multiple locations at the top of Callisto's atmosphere. These non-uniform electron fluxes likely cause inhomogeneous ionization of Callisto's atmosphere and may even contribute to irregular erosion of the surface. This paper is a companion to Liuzzo et al. (2019), who studied the dynamics of energetic ions near Callisto. • Callisto's perturbed electromagnetic environment strongly affects energetic electron dynamics. • Induced fields and Alfvén wings partially shield Callisto from impinging magnetospheric electrons. • Energetic electron precipitation onto Callisto's atmosphere is highly inhomogeneous. • Electrons may leave Callisto's local environment, bounce, and then return, causing asymmetric precipitation patterns. [ABSTRACT FROM AUTHOR]