JUpiter ICy Moons Explorer Research Articles

Role of Electron-Induced Coulomb Interactions to the Total SEU Rate During Earth and JUICE Missions

The contribution of Coulomb processes induced by incident electrons in single event upset (SEU) sensitivity is investigated. The case of 65-nm silicon on insulator (SOI) memory is studied. Several orbits (GPS, Jupiter Icy Moons Explorer's (JUICE's) orbits) are analyzed. The relative importance to the total SEU rate of electron, proton, and gamma environments is compared. SEU induced by electrons is obtained during Earth missions. In the environment of Jupiter, equivalent SEU sensitivities have been obtained between the studied device and the European Space Agency (ESA) SEU monitor. However, the relative importance of the physical processes involved is very different. Proton-induced SEU rates are estimated about one decade greater than electron-induced SEU rates. The Bremsstrahlung contribution has been found negligible in such an environment.

Titan's Interior Structure and Dynamics After the Cassini-Huygens Mission

The Cassini-Huygens mission that explored the Saturn system during the period 2004–2017 revolutionized our understanding of Titan, the only known moon with a dense atmosphere and the only body, besides Earth, with stable surface liquids. Its predominantly nitrogen atmosphere also contains a few percent of methane that is photolyzed on short geological timescales to form ethane and more complex organic molecules. The presence of a significant amount of methane and40Ar, the decay product of40K, argues for exchange processes from the interior to the surface. Here we review the information that constrains Titan's interior structure. Gravity and orbital data suggest that Titan is an ocean world, which implies differentiation into a hydrosphere and a rocky core. The mass and gravity data complemented by equations of state constrain the ocean density and composition as well as the hydrosphere thickness. We present end-member models, review the dynamics of each layer, and discuss the global evolution consistent with the Cassini-Huygens data. ▪ Titan is the only moon with a dense atmosphere where organic molecules are synthesized and have sedimented at the surface. ▪ The Cassini-Huygens mission demonstrated that Titan is an ocean world with an internal water shell and liquid hydrocarbon seas at the poles. ▪ Interactions between water, rock, and organics may have occurred during most of Titan's evolution, which has strong astrobiological implications. ▪ Data collected by the Dragonfly mission and comparison with the JUpiter ICy moons Explorer (JUICE) data for Ganymede will further reveal Titan's astrobiology potential.

Improvement of orbit determination using laser altimeter crossovers: JUICE mission case study

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.

Vacuum ultraviolet photoabsorption spectroscopy of space-related ices: formation and destruction of solid carbonic acid upon 1 keV electron irradiation

Context. Carbonic acid (H2CO3) is a weak acid relevant to astrobiology which, to date, remains undetected in space. Experimental work has shown that the β-polymorph of H2CO3 forms under space relevant conditions through energetic (UV photon, electron, and cosmic ray) processing of CO2- and H2O-rich ices. Although its α-polymorph ice has been recently reassigned to the monomethyl ester of carbonic acid, a different form of H2CO3 ice may exist and is synthesized without irradiation through surface reactions involving CO molecules and OH radicals, that is to say γ-H2CO3. Aims. We aim to provide a systematic set of vacuum ultraviolet (VUV) photoabsorption spectroscopic data of pure carbonic acid that formed and was destroyed under conditions relevant to space in support of its future identification on the surface of icy objects in the Solar System by the upcoming Jupiter ICy moons Explorer mission and on interstellar dust by the James Webb Space Telescope spacecraft. Methods. We present VUV photoabsorption spectra of pure and mixed CO2 and H2O ices exposed to 1 keV electrons at 20 and 80 K to simulate different interstellar and Solar System environments. Ices were then annealed to obtain a layer of pure H2CO3 which was further exposed to 1 keV electrons at 20 and 80 K to monitor its destruction pathway. Fourier-transform infrared (FT-IR) spectroscopy was used as a secondary probe providing complementary information on the physicochemical changes within an ice. Results. Our laboratory work shows that the formation of solid H2CO3, CO, and O3 upon the energetic processing of CO2:H2O ice mixtures is temperature-dependent in the range between 20 and 80 K. The amorphous to crystalline phase transition of H2CO3 ice is investigated for the first time in the VUV spectral range by annealing the ice at 200 and 225 K. We have detected two photoabsorption bands at 139 and 200 nm, and we assigned them to β-H2CO3 and γ-H2CO3, respectively. We present VUV spectra of the electron irradiation of annealed H2CO3 ice at different temperatures leading to its decomposition into CO2, H2O, and CO ice. Laboratory results are compared to Cassini UltraViolet Imaging Spectrograph observations of the 70−90 K ice surface of Saturn’s satellites Enceladus, Dione, and Rhea.

Energetic Neutral Atoms From Jupiter's Polar Regions

AbstractEnergetic Neutral Atom (ENA) cameras on orbiting spacecraft at Earth and Saturn helped greatly to diagnose these complex magnetospheres. Within this decade, the European Space Agency's Jupiter Icy Moons Explorer will make ENA imaging a major thrust in understanding Jupiter's complex magnetosphere. The present polar‐orbiting Juno mission at Jupiter carries no ENA camera. But, the Jupiter Energetic‐particle Detector Instrument is sensitive to >50 keV ENAs, provided there are no local charged particles to mask their presence. Juno offers great service to interpreting past serendipitous and future dedicated ENA imaging with its orbit providing unique viewing perspectives. Here we report Juno observations of ENAs from Jupiter's polar regions. These ENAs likely arise from energetic ions that nearly precipitate in the main auroral regions and mirror magnetically within, and charge exchange with, Jupiter's upper atmosphere. Jupiter proves itself different from Saturn, as ENAs generated from precipitating ions were not identified there.

Electron-Induced Upsets and Stuck Bits in SDRAMs in the Jovian Environment

This study investigates the response of synchronous dynamic random access memories to energetic electrons and especially the possibility of electrons to cause stuck bits in these memories. Three different memories with different node sizes (63, 72, and 110 nm) were tested. Electrons with energies between 6 and 200 MeV were used at RADiation Effects Facility (RADEF) in Jyväskylä, Finland, and at Very energetic Electron facility for Space Planetary Exploration missions in harsh Radiative environments (VESPER) in The European Organization for Nuclear Research (CERN), Switzerland. Photon irradiation was also performed in Jyväskylä. In these irradiation tests, stuck bits originating from electron-induced single-event effects (SEEs) were found, as well as single bit-flips from single electrons. To the best knowledge of the authors, this is the first time that stuck bits from single-electron events have been reported in the literature. It is argued in the article that the single-event bit-flips and stuck bits are caused by the same damage mechanism, which would be large displacement damage clusters, and that the two different fault modes represent different amounts of damage to the memory cell. After a large particle fluence, a rapid increase in the error rate was observed, originating from the accumulation of smaller displacement damage clusters in the memory cells. The 110-nm memory was a candidate component to fly on the European Space Agency (ESA) JUpiter ICy moons Explorer (JUICE) mission, so the SEE cross section as a function of electron energy was compared to the expected electron environment encountered by JUICE to estimate the error rates during the mission.

Observability of Ganymede's gravity anomalies related to surface features by the 3GM experiment onboard ESA's JUpiter ICy moons Explorer (JUICE) mission

The Geodesy and Geophysics of Jupiter and the Galilean Moons (3GM) experiment aboard the JUpiter ICy moons Explorer (JUICE) will measure the gravity fields of Europa, Callisto and Ganymede. For the first two moons the data will be acquired during flybys, while for Ganymede a 9-months orbital phase is planned. This latter phase is divided in a 5-month elliptical orbit phase (GEO) and a 4-month circular phase (GCO-500). The GCO-500 will provide the first gravity data from an orbiter for Ganymede, enabling the measurement of the Ganymede's gravity field up to the degree 35–45 of spherical harmonics expansion. The large amount of data collected by 3GM will provide enough details to potentially identify regional (hundreds of km) surface structures. Remarkably, Ganymede's outer ice shell is characterized by the presence of dark and bright terrains: evidence of older, dirty ice and younger, cleaner ice, respectively.In this work we investigate the possibility to detect gravity anomalies related to the surface distribution of bright and dark terrains using the 3GM data. By assuming a range of i) surface density contrasts for the dark and bright terrains based on an estimation of the impactors flux, ii) average surface topographies, iii) internal structure configurations, and comparing several models for the external gravity field of Ganymede, we simulate the expected gravity field as it would be reconstructed by JUICE. Our results show that 3GM data might allow to discriminate and separate the gravitational contributions from the deep interior and the surface distribution of dark and bright terrains.

A global system of furrows on Ganymede indicative of their creation in a single impact event

Furrows are a concentric system of tectonic troughs, and are the oldest recognizable surface feature on Ganymede. We analyzed the distribution of furrows utilizing Voyager and Galileo images and found that furrows over Ganymede's surface are part of a global concentric circular structure. If this multi-ring structure is impact origin, this is the largest impact structure identified so far in the solar system. Deviations of the shapes of the furrows from the concentricity are small everywhere, which implies that the relative location of the blocks of the dark terrains over the entire surface of Ganymede has not changed appreciably even during formation of the bright terrains. The estimate of the impactor size is difficult, but an 150 km-radius impactor is consistent with the observed properties of furrows. The furrow-forming impact should have significant effects on the satellite's geological and internal evolution, which are expected to be confirmed by future explorations of Jupiter's icy moons, such as the JUICE (Jupiter Icy moon Explorer) or Europa Clipper mission.

Preliminary estimation of the detection possibilities of Ganymede’s water vapor environment with MAJIS

The exosphere of Ganymede is the interface region linking the moon’s icy surface to Jupiter’s magnetospheric environment. Its characterization is of key importance to achieve a full understanding of the ice alteration processes induced by the radiation environment. Several scientific instruments that will operate on board the upcoming Jupiter Icy Moons Explorer (JUICE) mission, selected by ESA in the context of its Cosmic Vision programme, have the potential to study Ganymede’s exosphere. Among them, the Moons And Jupiter Imaging Spectrometer (MAJIS) will have the chance to investigate the composition of the moon’s exospheric components and the emission of water molecules. The exospheric water density profile, as obtained from current models, is a crucial parameter for the estimation of the expected signal to noise ratio related to the actual measurement. In lack of an adequate number of Ganymede’s observations from past missions, there is a general difficulty in constraining current exosphere models which are based, in general, on different scenarios and considerations and often show large discrepancies in the estimated spatial distribution of the neutral environment. In this work, we make a preliminary estimation of the expected IR emission from exospheric water molecules, using different modelled density profiles, and we speculate on the possibility of JUICE/MAJIS to detect it. An exercise on the potential plume detection capabilities of MAJIS is also performed. The first necessary step for performing these calculations is a rough comparison of the existing models of Ganymede’s water vapor exosphere. We discuss the characteristics of the neutral environment as derived from different exospheric models available in literature, the role of the ion-surface interactions in the H2O exosphere generation, and the related implications also in view of future observations. We then use the model outputs to estimate different scenarios for the expected non-Local Thermal Equilibrium (non-LTE) emission from these molecules. The results of this study can be of help during the JUICE observation planning phase.

Beam tests of a prototype of the Radiation Hard Electron Monitor to be flown in the JUICE mission

Radiation Hard Electron Monitor (RADEM) is a radiation monitor dedicated to the ESA, Jupiter Icy Moons Explorer (JUICE) space mission. Its purpose, as a part of the JUICE environmental monitor system, is to provide precise information of Jupiter radiation belts such as particle fluxes, energy range, species and directionality. RADEM consists of three independent detector systems: the Proton and Heavy Ion Detector Head (P&HIDH), the Electron Detector Head (EDH), and the Directionality Detector Head (DDH). Each of them has a dedicated, radiation-hard IDE3466 ASIC responsible for the readout. In this paper, we compare the first beam tests results with Geant4 simulations to understand the instrument response and to validate the simulation mass model.

Effect of the 3D distribution on water observations made with the SWI

Context. Characterising and understanding the atmospheres of Jovian icy moons is one of the key exploration goals of the Submillimetre Wave Instrument (SWI), which is to be flown on ESA’s Jupiter Icy Moons Explorer (JUICE) mission. Aims. The aim of this paper is to investigate how and under which conditions a 3D asymmetric distribution of the atmosphere may affect the SWI observations. In this work we target the role of phase angle for both nadir and limb geometries for unresolved and partially resolved disc observations from large distances. Methods. We adapted the LIME software package, a 3D non-local thermodynamical equilibrium radiative transfer model, to evaluate ortho-H2O populations and synthesise the simulated SWI beam spectra for different study cases of Ganymede’s atmosphere. The temperature and density vertical distributions were adopted from a previous work. The study cases presented here were selected according to the distance and operational scenarios of moon monitoring anticipated for SWI during the Jupiter phase of the JUICE mission. Results. We demonstrate that nadir and limb observations at different phase angles will modify the line amplitude and width. Unresolved observations where both absorption against surface continuum and limb emission contributes within the beam will lead to characteristic line wing emission, which may also appear in pure nadir geometry for specific phase angles. We also find that for Ganymede, the 3D non-local thermodynamical equilibrium populations are more highly excited in the upper atmosphere near the sub-solar region than they are in 1D spherically symmetric models. Finally, the 3D radiative transfer is better suited to properly simulate spectral lines for cases where density or population gradients exist along the line of sight.

Ganymede's gravity, tides and rotational state from JUICE's 3GM experiment simulation

The JUpiter Icy Moons Explorer (JUICE) is a European Space Agency (ESA) mission that will launch in 2022 and arrive in the Jovian system in 2029 to investigate Jupiter's icy satellites. The mission will perform flybys of the icy moons Europa, Callisto and Ganymede before being inserted into a 280-day orbit around Ganymede: 150 days in Elliptical Orbit (GEO) followed by 130 days Circular Orbit at 500 km (GCO-500). During the orbital phase, JUICE will investigate the moon's surface, interior and exosphere, carrying out for the first time a complete characterization of an icy satellite. A suite of field and particle instruments will characterize the plasma and magnetic environment around the body. The 3GM experiment on board the spacecraft will exploit the GCO-500 phase to collect accurate Doppler and range measurements to determine the moon's orbit, gravity field and tide, therefore providing crucial information to accurately model its internal structure. The simulations carried out reveal that the moon's gravity field can be determined up to degree and order 40, depending on the magnitude of the gravity spectrum. The Love number k2, modelling the gravitational response to eccentricity-driven, time-variable gravity gradient from Jupiter, is determined with an accuracy of σk2∼10−4. The obliquity, φ, and the libration at orbital period, ϕ, can be retrieved with a level of uncertainty of 1 and 2 μrad, respectively. Because of the 97 m2 solar panels and the ensuing large area-to-mass ratio, JUICE will be affected by neutral particle drag. Here, we also assess the potential effect of spacecraft drag due to Ganymede's tenuous exosphere, which ranges between 10−17−10−16kg/m3 and generates an average drag of ∼4⋅10−12m/s2, in the GCO-500 phase.

Favorable Conditions for Magnetic Reconnection at Ganymede's Upstream Magnetopause

AbstractGanymede is the only Solar System moon known to generate a permanent magnetic field. Jovian plasma motions around Ganymede create an upstream magnetopause, where energy flows are thought to be driven by magnetic reconnection. Simulations indicate Ganymedean reconnection events may be transient, but the nature of magnetopause reconnection at Ganymede remains poorly understood, requiring an assessment of reconnection onset theory. We present an analytical model of steady‐state conditions at Ganymede's magnetopause, from which the first Ganymedean reconnection onset assessment is conducted. We find that reconnection may occur wherever Ganymede's closed magnetic field encounters Jupiter's ambient magnetic field, regardless of variations in magnetopause conditions. Unrestricted reconnection onset highlights possibilities for multiple X lines or widespread transient reconnection at Ganymede. The reconnection rate is controlled by the ambient Jovian field orientation and hence driven by Jupiter's rotation. Future progress on this topic is highly relevant for the JUpiter ICy moon Explorer mission.

An Approach Based on Multiobjective Genetic Algorithms to Schedule Observations in Planetary Remote Sensing Missions

Data acquisition in planetary remote sensing missions is influenced by complex environmental resource- and instrument-specific constraints. This impedes to perform observations at any given time during the mission and with any of the instruments composing the scientific payload. This article presents an approach to automatic scheduling of acquisition operations of a remote sensing instrument composing the scientific payload of a mission. The methodology first subdivides the long available observation time intervals into shorter segments and then performs a selection of them, producing an acquisition schedule, optimized with respect to scientific requirements, instrument characteristics, and mission constraints. The scheduling problem is modeled as a multiobjective optimization problem and solved by using Genetic Algorithms (GAs). GAs are able to efficiently explore the solution space by considering different competing objective functions, reaching high-quality solutions. These solutions represent different optimized tradeoffs among the considered instrument-specific quality metrics. The approach is demonstrated on the operations of Radar for Icy Moons Exploration (RIME), a radar sounder onboard Jupiter Icy Moons Explorer. The obtained results show a high potential of the proposed methodology.

Assessing the detectability of Europa’s eutectic zone using radar sounding

Radar sounding is a geophysical method capable of directly imaging subsurface interfaces within the ice shell of the icy moons, including Jupiter’s moon, Europa. For this reason, both the European Space Agency’s JUpiter ICy moons Explorer and the National Aeronautics and Space Administration’s Europa Clipper missions have ice penetrating radar sounders in their payloads. In addition to the ice–ocean interface and shallow water lenses, liquid water in the eutectic zone of Europa’s ice shell could also be a target for radar sounding investigations. However, the wide range of possible configurations for eutectic-zone water bodies and the overlying ice make their absolute echo strength difficult to predict. To address this challenge, we employ a suite of simple water configurations and scattering models to bound the eutectic detectability in terms of its effective reflectivity. We find that, for each configuration, a range of physically plausible eutectic parameters exist that could produce detectable echoes, with effective reflectivity values greater than -50 dB at HF or VHF frequencies.

Predicting the effect of radiation damage on dark current in a space-qualified high performance CMOS image sensor

The CIS115 is a Teledyne-e2v CMOS image sensor with 1504 × 2000 pixels of 7 μm pitch. It has a high optical quantum efficiency owing to a multi-layer anti-reflective coating and its backside illuminated construction, and low dark current due to its pinned photodiode 4T pixel architecture. The sensor operates in rolling shutter mode with a frame rate of up to 7.5 fps (if using the whole array), and has a low readout noise of ∼5 electrons rms. The CIS115 has been selected for use within the JANUS instrument, which is a high resolution camera due to launch on board ESA's JUpiter ICy moons Explorer (JUICE) spacecraft in 2022. After an interplanetary transit time of over 7 years, JUICE will spend 3.5 years touring the Jovian system, studying three of the Galilean moons in particular: Ganymede, Callisto and Europa. During this latter part of the mission, the spacecraft and hence the CIS115 sensor will be subjected to the significant levels of trapped radiation surrounding Jupiter. Gamma and proton irradiation campaigns have therefore been undertaken in order to evaluate both ionising and non-ionising dose effects on the CIS115's dark current performance. Characterisations were carried out at expected mission operating temperatures (−35 ± 10̂C) both prior to and post-irradiation. Models of the resulting degradation in dark current behaviour will be combined with expected doses during the JUICE mission in order to predict the performance of the CIS115 at the mission end-of-life.

Detection efficiency of microchannel plates to penetrating radiation in space

Space-based instruments for detection of photons, plasma, and energetic neutral atom imaging include electron multiplier detectors that are subject to increased transient noise, long-term degradation, and even potential failure due to the substantial fluxes of high-energy particles that penetrate the instrument in the space environment. The most commonly used electron multiplier detectors are multi-channel plates (MCP). These detectors are sensitive not only to the incident energetic charged particles themselves but also to the final end-product energy deposited by energetic electrons, ions, and X-rays/gammas. The resulting radiation-induced background noise can potentially contaminate the science signal. This issue constitutes undoubtedly one of the main challenges together with the radiation hardness of the electronics for particle instruments onboard future missions to Jupiter like the European Space Agency (ESA) Jupiter ICy moon Explorer (JUICE), and requires dedicated and innovative radiation mitigation techniques (e.g., multiple coincidence, anti-coincidence) far beyond the simple passive shielding techniques commonly used to protect electronics and other subsystems against total ionizing dose (TID). The accurate response (i.e., efficiency) of MCP detectors against high-energy particles is, however, not well known, with limited estimates available in the literature. This makes it complicated in particular to reliably predict the signal–noise ratio (SNR) of the instrument, and, hence, ensure that the instrument will return useful scientific data when operated in the Jovian magnetosphere. We describe and report in the present paper the results of an experiment in which we measured the response of Photonis MCP detectors to 300–1500 keV electrons and 500 keV photons (gamma rays) using a Van de Graff electron gun available at ONERA, Toulouse, France. The efficiency of the tested MCP for high-energy electrons is about 20–30% below 100 keV and is reduced to 10% for electron energies greater than 100 keV. The efficiency of the tested MCP for the gamma radiation of 500 keV energy is approximately 0.1%.

The Ganymede laser altimeter (GALA): key objectives, instrument design, and performance

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 $$5.5\pm 2.5$$ 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.

Beam test results of the RADEM Engineering Model

ESAs next class-L mission to the Jovian system, the Jupiter Icy Moons Explorer (JUICE), will collect valuable data while orbiting Jupiter and three its moons for a period of three and a half years. RADEM, the Radiation Hard Electron Monitor is being developed to provide housekeeping information for the mission. It will also gather valuable scientific data on the energetic radiation environment of the Jovian system for its full duration. The Jovian radiation environment, dominated by electrons, results from Jupiter strong magnetic field and its interaction with the Galilean moons. So far, only the Galileo spacecraft performed long-term measurements of the radiation environment showing that it is extremely hazardous and complex.RADEM features four detector heads: the Proton Detector Head to measure protons energies, the Ion Detector Head to measure ion content up to oxygen; the Electron Detector head to perform electron spectral measurements; and the Directionality Detector Head to correct for electron flux angular dependences. The detectors readout are three newly custom designed ASIC IDE3466. In this work, RADEM overall properties and Engineering Model radiation tests results are presented.

Three‐Dimensional Modeling of Callisto's Surface Sputtered Exosphere Environment

AbstractWe study the release of various elements from Callisto's surface into its exosphere by plasma sputtering. The cold Jovian plasma is simulated with a 3‐D plasma‐planetary interaction hybrid model, which produces 2‐D surface precipitation maps for magnetospheric H+, O+, O++, and S++. For the hot Jovian plasma, we assume isotropic precipitation onto the complete spherical surface. Two scenarios are investigated: one where no ionospheric shielding takes place and accordingly full plasma penetration is implemented (no‐ionosphere scenario) and one where an ionosphere lets virtually none of the cold plasma but all of the hot plasma reach Callisto's surface (ionosphere scenario). In the 3‐D exosphere model, neutral particles are sputtered from the surface and followed on their individual trajectories. The 3‐D density profiles show that whereas in the no‐ionosphere scenario the ram direction is favored, the ionosphere scenario produces almost uniform density profiles. In addition, the density profiles in the ionosphere scenario are reduced by a factor of ∼2.5 with respect to the no‐ionosphere scenario. We find that the Neutral Gas and Ion Mass Spectrometer, which is part of the Particle Environment Package on board the JUpiter ICy moons Explorer mission, will be able to detect the different sputter populations from Callisto's icy surface and the major sputter populations from Callisto's nonicy surface. The chemical composition of Callisto's exosphere can be directly linked to the chemical composition of its surface and will offer us information not only on Callisto's formation scenario but also on the building blocks of the Jupiter system.