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Jupiter and its moons are a complex dynamical system that include several phenomena like tides interactions, moon’s librations and resonances. One of the most interesting characteristics of the Jovian system is the presence of the Laplace resonance, where the orbital periods of Ganymede, Europa and Io maintain a 4:2:1 ratio, respectively. It is interesting to study the role of the Laplace resonance in the dynamic of the system, especially regarding the dissipative nature of the tidal interaction between Jupiter and its closest moon, Io. The secular orbital evolution of the Galilean satellites, and so the Laplace resonance, is strongly influenced by the tidal interaction between Jupiter and its moons, especially with Io. Numerous theories have been proposed regarding this topic, but they disagree about the amount of dissipation of the system, therefore about the magnitude and the direction of the evolution of the system, mainly because of the lack of experimental data. The future ESA JUICE space mission is a great opportunity to solve this dispute. The data that will be collect during the mission will have an exceptional accuracy, allowing to investigate several aspects of the dynamics the system and possibly the evolution of Laplace Resonance of the Galilean moons. This work will focus on the gravity estimation and orbit reconstruction of the Galilean satellites by precise orbit determination of the JUICE mission during the Jovian orbital phase using radiometric data.

Europa, one of Jupiter's Galilean moons, has twice as much liquid water as Earth's oceans, if not more. An ocean estimated to be anywhere from 40 to 100 miles (60 to 150 kilometers) deep spans the entire moon, locked beneath an icy surface over a dozen kilometers thick. The only direct evidence for this ocean is the plumes of water that occasionally erupt through cracks in the ice, jetting as high as 200 km above the surface.

É crescente o número de interessados em coletar imagens do céu, seja para uso amador oucientífico. Com isto, várias tecnologias têm sido utilizadas para capturar e processar imagens de astros, desde câmeras de alto custo, em grandes observatórios com telescópios enormes, até câmeras digitais pequenas e sensores CCDs. É evidente que o acesso ao campo da astrofotografia possui ainda uma barreira financeira, tanto para astrônomos amadores quanto para pesquisas em instituições de ensino. Sendo assim, este trabalho busca elaborar uma metodologia simples que exemplifica técnicas de captura e processamento de astrofotografias utilizando equipamentos de baixo custo. Para isto, são realizadas astrofotografias utilizando duas câmeras digitais pequenas acopladas a um telescópio, que posteriormente foram processadas e analisadas. Foram obtidas astrofotografias da Lua, Saturno, Júpiter e suas luas Galileanas. Além disso, calculou-se os diâmetros de várias crateras lunares, a fim de exemplificar a aplicação do método na extração de dados físicos das imagens, assim como evidenciou-se o movimento orbital das luas de Júpiter (Europa, Ganimedes, Io e Calisto). A metodologia apresentada se mostrou eficiente ao capturar, processar e extrair dados físicos de astrofotografias, podendo ser aplicadas tantopara fins artísticos quanto para o ensino de Astronomia.

Jupiter's Galilean satellite Io is one of the most remarkable objects in our Solar System. The tidal heating Io undergoes through its orbital resonance with Europa and Ganymede has resulted in a body rich in active silicate volcanism. Over the past decades, Io has been observed from ground-based and Earth-orbiting telescopes and by several spacecraft. In this review we summarize the progress made toward our understanding of the physical and chemical processes related to Io and its environment since the Galileo era. Io science has been revolutionized by the use of adaptive optics techniques on large, 8- to 10-m telescopes. The resultant ever-increasing database, mapping the size, style, and spatial distribution of Io's diverse volcanoes, has improved our understanding of Io's interior structure, its likely composition, and the tidal heating process. Additionally, new observations of Io's atmosphere obtained with these large optical/infrared telescopes and the Atacama Large Millimeter/submillimeter Array reveal the presence of volcanic plumes, the (at times) near-collapse of Io's atmosphere during eclipse, and the interactions of plumes with the sublimation atmosphere. ▪ Extensive new data sets of Io at ultraviolet, mid- to near-infrared, and radio wavelengths have been gathered since the Galileo era. ▪ New data and models inform us about tidal heating, surface properties, and magma composition across Io—although key questions remain. ▪ Atmospheric observations indicate a dominant sublimation-supported component and reinforce the presence of stealth volcanism. ▪ Observations of volcanic plumes show high gas velocities (up to ∼1 km/s) and their effect on Io's atmosphere.

When our school implemented AP Physics 1, I wanted to include a project that would extend over time, use more advanced data analysis, and teach students about handling experimental error. Using a donated 5-inch Newtonian telescope and an entry-level digital camera, the students gathered data from digital images of the four Galilean moons, Io, Europa, Ganymede, and Callisto (see Fig. 1), to verify Kepler’s third law of planetary motion (T2=Kr3). Simulation software could have been used. Among others, Project CLEA (Contemporary Laboratory Experiences in Astronomy) seems to be a favorite that includes verifying Kepler’s third law using the orbits of the Galilean moons. Galileo measured the moons’ periods with his telescope. My students could do the same with modern equipment. The investigation started with a purely Keplerian analysis of the data, then to a Newtonian analysis leading to accurate orbital properties of the Galilean moons and Jupiter’s mass. Once the images have been obtained, they can be used each year.

This paper presents the method created by the National University of Defense Technology (NUDT) team in the 10th China Trajectory Optimization Competition, which entails a 3-year observation mission of 180 regions on Jupiter. The proposed method can be divided into three steps. First, a preliminary analysis and evaluation via an analytical method is undertaken to decide whether the third subtask of the mission, i.e., exploring the Galilean moons, should be ignored. Second, a near-optimal orbit for magnetic field observation is designed by solving an analytical equation. Third, a set of observation windows and their sequence are optimized using a customized genetic algorithm. The final index obtained is 354.505, ranking second out of all teams partaking in the competition.

We investigate whether the regular Galilean satellites could have formed in the dead zone of a circumplanetary disc. A dead zone is a region of weak turbulence in which the magnetorotational instability (MRI) is suppressed, potentially an ideal environment for satellite formation. With the grid-based hydrodynamic code, FARGO3D, we examine the evolution of a circumplanetary disc model with a dead zone. Material accumulates in the dead zone of the disc leading to a higher total mass and but a similar temperature profile compared to a fully turbulent disc model. The tidal torque increases the rate of mass transport through the dead zone leading to a steady state disc with a dead zone that does not undergo accretion outbursts. We explore a range of disc, dead zone and mass inflow parameters and find that the maximum mass of the disc is around 0.001 MJ . Since the total solid mass of such a disc is much lower, we find that there is not sufficient material in the disc for in situ formation of the Galilean satellites and that external supplement is required., Comment: 10 pages, 6 figures

This paper presents the methods and results submitted by the winning team from Harbin Institute of Technology of the 10th China Trajectory Optimization Competition (CTOC10). The problem posed by CTOC10 requires exploring the Jupiter system using a combined spacecraft. The exploration mission consists of the detection of Jupiter’s magnetic field and an exploration of the Galilean moons. The mission is completed through three steps: problem analysis, orbital design process, and data processing. The orbital design process is mainly divided into four parts, namely, repeating ground-track orbit design, gravity-assisted orbit design, initial orbit parameter selection, and local optimization adjustment. The designed orbit is then evaluated using a heuristic optimization algorithm applied during the data processing. Finally, six full-coverage observations of Jupiter’s magnetic field are realized under the constraints of fuel and time. The final index of the submitted result is 357.8067.

We consider space expeditions with a long-term spacecraft stay near the studied celestial body (artificial satellites of small bodies of the Solar System), or expeditions with a possible spacecraft landing on the surface of the celestial body (for example, the ESA Jovian Icy Moon Explorer JUICE mission, and the Russian prospective project Laplace‑P). An effective formalism is proposed for creating adaptive search scenarios for low-cost combined spacecraft trajectories, focused on the possibility of using high-performance computing resources of the computer experimentation. Examples are given of the implementation of this formalism for searching for combinations of interlunar gravitational maneuvers in the Jovian system with the aim of entering the orbit of the Jovian moon’s artificial satellite.

The four Galilean moons of Jupiter were discovered by Galileo in the early 17th century, and their motion was first seen as a miniature solar system. Around 1800 Laplace discovered that the Galilean motion is subjected to an orbital \begin{document}$ 1{:}2{:}4 $\end{document} -resonance of the inner three moons Io, Europa and Ganymedes. In the early 20th century De Sitter gave a mathematical explanation for this in a Newtonian framework. In fact, he found a family of stable periodic solutions by using the seminal work of Poincare, which at the time was quite new. In this paper we review and summarize recent results of Broer, Hansmann and Zhao on the motion of the entire Galilean system, so including the fourth moon Callisto. To this purpose we use a version of parametrised Kolmogorov-Arnol'd-Moser theory where a family of multi-periodic isotropic invariant three-dimensional tori is found that combines the periodic motions of De Sitter and Callisto. The \begin{document}$ 3 $\end{document} -tori are normally elliptic and excite a family of invariant Lagrangean \begin{document}$ 8 $\end{document} -tori that project down to librational motions. Both the \begin{document}$ 3 $\end{document} - and the \begin{document}$ 8 $\end{document} -tori occur for an almost full Hausdorff measure set in the product of corresponding dimension in phase space and a parameter space, where the external parameters are given by the masses of the moons.

Planetary space, a critical region of mass and energy exchange between the planet and the interplanetary space, is an integral part of the planetary multi-layer coupling system. Atmospheres of different compositions and plasmas of different densities and energies exist in planetary space, where mass transportation at different temporal and spatial scales and various energy deposition and dissipation processes occur. These processes are driven by the changes in the solar wind and the internal driving forces of the planet. Knowledge pertaining to the global mass and energy transportation in planetary space is essential to investigate the mass escape from the planets. Understanding the forces and physical processes that drive changes in the planetary space environment is not only beneficial to protecting the life, technical systems, and infrastructures on the Earth, but is also helpful in understanding the past and future. In this regards, the systematic and overall view of planetary space environments is necessary for planetary science. Optical remote sensing implies a measurement made by indirect or “remote” means, which relies upon either emitted, reflected, or scattered optical radiation. There are three main types of optical remote sensing technologies, namely imaging (photography), spectrograph, and spectrographic imaging. Scientific application of optical remote sensing dates back to 1906 when G. Galilei constructed the first astronomical telescope, using which he discovered the four Galilean satellites of Jupiter and the phase variation of Venus. Since then, several discoveries in planetary science have been made by means of optical remote sensing, such as the discovery of new planets and their moons, the discovery of the primary compositions of planetary atmospheres, global convection of cold plasma in Earth’s space, the discovery of planetary aurora (Earth, Mars, Jupiter, Saturn) and volcanic activity on Io, and water eruption on Enceladus. The optical remote sensing method overcomes the difficulties of capturing global views and distinguishing spatial and temporal variations in in-situ particle and field detections. Furthermore, through an overview of the history of planetary optical remote sensing, we propose a development strategy for planetary optical remote sensing, in China, based on the national deep-space exploration plan. A “Quaternity” planetary optical detection system that integrates ground-based, balloon-borne, space-based, and moon-based optical remote sensing is proposed. For example, the Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS) is planning to construct a ground-based optical telescope with an aperture of ~1.5 m in Northwest China to monitor the volcanic activity on Io and to conduct other planetary observations. As the first planetary optical remote sensing project in China, the balloon-borne planetary optical remote sensing for the Scientific Experiment System in Near Space (SENSE) Program is introduced in detail. The SENSE Program is a five-year Strategic Priority Research Program of the Chinese Academy of Sciences, which began in 2018. A balloon-borne Planetary Atmospheric Spectroscopic Telescope (PAST) with an aperture of 0.8 m will be launched into the stratosphere at the height of 35–40 km to image the planetary atmosphere and plasma in the ultraviolet and visible range. The main scientific target of PAST is to comparatively study the diversity of the planetary space environment and their different drivers. Test and scientific flights are scheduled in 2021 and 2022 in Northwest China and potentially in polar regions. By using the data from PAST and in combination with other data (such as Jupiter’s auroral images from the Hubble Space Telescope, Mars’ space environment data from Mars Atmosphere and Volatile Evolution mission, and Jupiter’s space environment data from Juno mission), the couplings between planetary atmosphere and plasma will be investigated to characterize the diversity of the evolution of the planetary space environment.

In the search for moons around extrasolar planets, astronomers are confronted with a stunning observation. Although 3400 of the 4500 exoplanets were discovered with the transit method and although there are well over 25 times as many moons than planets known in the Solar System (two of which are larger than Mercury), no exomoon has been discovered. In the search for exoplanet transits, stellar light curves are usually phase-folded over a range of trial epochs and periods. This approach, however, is not applicable in a straightforward manner to exomoons. Planet-moon transits either have to be modeled in great detail (including their orbital dynamics, mutual eclipses etc.), which is computationally expensive, or key simplifications have to be assumed. One such simplification is to search for moon transits outside of the planetary transits. The question we address in this report is how much in-transit data of an exomoon remains uncontaminated by the near-simultaneous transits of its host planet. We develop an analytical framework and test our results with a numerical planet-moon transit simulator. For exomoons similar to the Galilean moons, only a small fraction of their in-transit data is uncontaminated by planetary transits: 14% for Io, 20% for Europa, 42% for Ganymede, and 73% for Callisto. The S/N of an out-of-planetary-transit folding technique is reduced compared to a full transit model to about 38% (Io), 45% (Europa), 65% (Ganymede), and 85% (Callisto), respectively. For the Earth's Moon, we find an uncontaminated data fraction of typically just 18% and a resulting S/N reduction to 42%. These values are astonishingly small. The gain in speed for any exomoon transit search algorithm that ignores the planetary in-transit data comes at the heavy price of losing a substantial fraction of what is supposedly a tiny signal in the first place., Comment: accepted in A&A, 5 pages, 4 Figures (2 col, 2 b/w)

When reconstructing natural satellites' ephemerides from space missions' tracking data, the dynamics of the spacecraft and natural bodies are often solved for separately, in a decoupled manner. Alternatively, the ephemeris generation and spacecraft orbit determination can be performed concurrently. This method directly maps the available data set to the estimated parameters' covariances while fully accounting for all dynamical couplings. It thus provides a statistically consistent solution to the estimation problem, whereas this is not directly ensured with the decoupled strategy. For the Galilean moons in particular, the JUICE mission provides a unique, although challenging, opportunity for ephemerides improvement. For such a dynamically coupled problem, choosing between the two state estimation strategies will be influential. This paper quantifies the Galilean moons' state uncertainties attainable when applying a coupled estimation strategy to simulated JUICE data, and discusses the challenges that remain to be addressed to achieve such a coupled solution from real observations. We first provide a detailed, explicit formulation for the coupled approach, which was still missing in the literature although already used in past studies. We then assessed the relative performances of the two ephemerides generation techniques for the JUICE test case. To this end, we used both decoupled and coupled models on simulated JUICE radiometric data. We compared the resulting covariances for the Galilean moons' states, and showed that the decoupled approach yields slightly lower formal errors for the moons' tangential positions. However, the coupled model can reduce the state uncertainties by more than one order of magnitude in the radial direction (i.e. towards the central body). It also proved more sensitive to the dynamical coupling between Io, Europa and Ganymede, allowing the state solutions for the first two moons to fully benefit from JUICE orbital phase around Ganymede. On the other hand, we showed that the choice of state estimation methods does not strongly affect the moons' gravity field determination. Many issues still remain to be solved before a concurrent estimation strategy can be successfully applied, especially to reconstruct the moons’ dynamics over long timescales. Nonetheless, our analysis highlights promising ephemerides improvements and thus motivates future efforts to reach a coupled state solution for the Galilean moons.

Geophysics-focused missions and improved geophysical data sets are critical for the future exploration of icy ocean worlds. Of particular interest is the exploration of the Galilean moon, Europa, and the Saturnian moons, Titan and Enceladus. These bodies likely have geologically active surfaces and may harbor habitable subsurface environments. Placing any candidate signatures for life in context requires further knowledge of the interior of these worlds. While the surfaces of these bodies have been mapped, their interiors remain poorly understood. Geophysical approaches such as geodesy, seismology, ice-penetrating radar and altimetry measurements, and electromagnetometry would provide critical information regarding the interior of these icy ocean worlds. The approaches described below would answer key science questions regarding ice shell and ocean dynamics, internal structure and interior layer thicknesses, near-surface structure, and how material from the deep interior might be exchanged with the surface. Here we outline the geophysical environments of Enceladus, Europa, and Titan; some outstanding science questions that remain to be addressed; and examples of the geophysical approaches that can provide the context to better understand icy ocean worlds.

This review of miniaturised instrumentation is motivated by the ongoing and forthcoming exploration of the confirmed, or candidate ocean worlds of the Solar System. It begins with a section on the evolution of instrumentation itself, ranging from the early efforts up to the current rich-heritage miniaturised mass spectrometers approved for missions to the Jovian system. The geochemistry of sulphur stable isotopes was introduced for life detection at the beginning of the present century. Miniaturised instruments allow the measurement of geochemical biosignatures with their underlying biogenic coding, which are more robust after death than cellular organic molecules. The role of known stable sulphur isotope fractionation by sulphate-reducing bacteria is discussed. Habitable ocean worlds are discussed, beginning with analogies from the first ocean world known in the Solar System that has always being available for scientific exploration, our own. Instrumentation can allow the search for biosignatures, not only on the icy Galilean moons, but also beyond. Observed sulphur fractionation on Earth suggests a testable “Sulphur Hypothesis”, namely throughout the Solar System chemoautotrophy, past or present, has left, or are leaving biosignatures codified in sulphur fractionations. A preliminary feasible test is provided with a discussion of a previously formulated “Sulphur Dilemma”: It was the Galileo mission that forced it upon us, when the Europan sulphur patches of non-ice surficial elements were discovered. Biogenic fractionations up to and beyond δ34S = −70‰ denote biogenic, rather than inorganic processes, which are measurable with the available high sensitivity miniaturised mass spectrometers. Finally, we comment on the long-term exploration of ocean worlds in the neighbourhood of the gas and ice giants.

New versions of the ephemerides for the Galilean satellites of Jupiter (Io, Europa, Ganymede, and Callisto) constructed by numerically integrating the equations of motion of the satellites are presented. The satellite motionmodel takes into account the non-sphericity of Jupiter, the mutual perturbations of the satellites, and the perturbations from the Sun and major planets. The initial satellite motion parameters have been improved based on all the available series of ground-based optical observations spanning the interval 1891-2017, spacecraft observations, and radar observations. As a result, the coefficients of the expansion of the satellite coordinates and velocities in terms of Chebyshev polynomials in the interval 1891- 2025 have been obtained. The root-mean-square errors of the observations and the graphs of comparison of the constructed ephemerides both with the observations and with Lainey's numerical ephemerides are presented. The constructed ephemerides are publicly accessible.

We present the results of observations of the Galilean moons of Jupiter carried out at the Normal Astrograph of the Pulkovo Observatory in 2018. We obtained 452 positions of the Galilean moons of Jupiter in the Gaia DR1 catalog system (ICRF, J2000.0) and 671 differential coordinates of the satellites relative to each other. The obtained mean errors in the satellites’ normal positions on the right ascension and declination, which demonstrate the intrinsic convergence of the observational results, are eα = 0.003′′ and eδ = 0.003′′, respectively, for the entire observational period. The errors of one difference are σα = 0.070′′, and σδ = 0.067′′, respectively. The equatorial coordinates of the moons were compared to eight motion theories of planets and satellites. On average, the (O–C) residuals in the both coordinates relative to the motion theories are 0.014′′. The best agreement with observations is achieved by combination of all four motion theories of satellites with the planetary theory EPM2017, which yields average (O–C) residuals of approximately 0.01′′ for each of them. The new results were compared to those of the 2016−2017 observational season. As in the past, peculiarities in the behavior of the (O–C) residuals for Io and Ganymede have been noticed.

The Solar System gas giants are each surrounded by many moons, with at least 50 prograde satellites thought to have formed from circumplanetary material. Just like the Sun is not the only star surrounded by planets, extrasolar gas giants are likely surrounded by satellite systems. Here, we report on ALMA observations of four, 6 pages, 3 figures, accepted for publication in MNRAS

The Jovian Infrared Auroral Mapper (JIRAM) on board Juno is a spectro-imager which is observing theatmosphere of Jupiter and its auroral emission using its two imagers in the L (3.3-3.6μm) and M bands (4.5-5.0μm) and a spectrometer (2-5 μm spectral range).The highly elliptic orbit of Juno and the unprecedented resolution of the JIRAM imager allowed to retrievewealth of details about the morphology of moon-related aurorae. This phenomenon is due to the jovian magneticfield sweeping past the Galiean moons, which generate Alfven waves travelling towards the ionosphere and setup field aligned currents. When the associated electrons reach the ionosphere, they interact with the hydrogenand make it to glow. In particular, the tails of the footprints showed a spot-like substructure consistently, whichwere investigated using the L-band of the imager from perijove 4 to perijove 30. This feature was observed closeto the footprints, where the the typical distance between spots lies between 250km and 500km. This distancedecreases to 150km in a group of three observations in the northern emisphere when each moon is close to 250 ◦west longitude. No correlation with orbital parameters such as the longitude of the moons was found so far,which suggests that such morphology is almost purely due to ionospheric processes.Moreover, during PJ 13 a long sequence of images of the Io footprint was shot and it revealed that thesecondary spots appears to corotate with Jupiter. This behaviour is observed also during orbits 14 and 26.During these sequences JIRAM clearly observed the Io footprint leaving behind a trail of ”footsteps” as brightspots.The characteristics of these spots are incompatible with multiple reflection of Alfven waves between the twoemispheres. Instead, we are currently investigating ionospheric processes like the feedback instability (FI) as apotential candidate to explain the generation of the observed small scale structure. This process relies on localenhacement of conductivity in the ionosphere, which is affected by electron precipitation. Order of magnitudeestimates from the FI are compatible with the inter-spot distance and the stillness of the spots.

Occultations of the Jovian low frequency radio emissions by the Galilean moons have been observed by the PWS instrument of the Galileo spacecraft. We show that the ExPRES (Exoplanetary and Planetary Radio Emission Simulator) code accurately models the temporal occurrence of the occultations in the whole spectral range observed by Galileo/PWS. This validates of the ExPRES code. The method can be applied for preparing the JUICE moon flyby science operation planning. Occultations of the Jovian low frequency radio emissions by the Galilean moons have been observed by the PWS (Plasma Wave Science) instrument of the Galileo spacecraft. We show that the ExPRES (Exoplanetary and Planetary Radio Emission Simulator) code accurately models the temporal occurrence of the occultations in the whole spectral range observed by Galileo/PWS. This validates of the ExPRES code. In addition to supporting the analysis of the science observations, the method can be applied for preparing the JUICE moon flyby science operation planning., Accepted for publication in Planet. Space Sci. Supplementary material available at: https://doi.org/10.25935/8ZFF-NX36

We present thermal observations of Ganymede from the Atacama Large Millimeter Array (ALMA) in 2016-2019 at a spatial resolution of 300-900 km (0.1-0.2'' angular resolution) and frequencies of 97.5, 233, and 343.5 GHz (wavelengths of 3, 1.3, and 0.87 mm); the observations collectively covered all Ganymede longitudes. We determine the global thermophysical properties using a thermal model that considers subsurface emission and depth- and temperature-dependent thermophysical and dielectric properties, in combination with a retrieval algorithm. The data are sensitive to emission from the upper $\sim$0.5 meter of the surface, and we find a millimeter emissivity of 0.75-0.78 and (sub)surface porosities of 10-40%, corresponding to effective thermal inertias of 400-800 J m^{-2} K^{-1} s^{-1/2}. Combined with past infrared results, as well as modeling presented here of a previously-unpublished Galileo PPR nighttime infrared observation, the multi-wavelength constraints are consistent with a compaction profile whereby the porosity drops from ~85% at the surface to 10{+30/-10}% at depth over a compaction length scale of tens of cm. We present maps of temperature residuals from the best-fit global models which indicate localized variations in thermal surface properties at some (but not all) dark terrains and at impact craters, which appear 5-8 K colder than the model. Equatorial regions are warmer than predicted by the model, in particular near the centers of the leading and trailing hemispheres, while the mid-latitudes (~30-60 degrees) are generally colder than predicted; these trends are suggestive of an exogenic origin., Comment: Fixed typo in Eqn 1; article published in Planetary Science Journal, Vol 2, Issue 1, id.5 (Feb 2021)

Io is the most volcanically-active object in the solar system. The moon ejects a tonne per second of sulphur-rich gases that fill the vast magnetosphere of Jupiter and drives million-amp electrical currents that excite strong auroral emissions. We present the case for including a detailed study of Io within Voyage 2050 either as a standalone mission or as a contribution to a NASA New Frontiers mission, possibly within a Solar System theme centred around current evolutionary or dynamical processes. A comprehensive investigation will provide answers to many outstanding questions and will simultaneously provide information on processes that have formed the landscapes of several other objects in the past. A mission investigating Io will also study processes that have shaped the Earth, Moon, terrestrial planets, outer planet moons, and potentially extrasolar planets. The aim would be simple – tracing the mass and energy flows in the Io-Jupiter system.

Plumes spewing water high above Europa's surface have been inferred from several observation campaigns in the past decade. Whereas the occasional existence of plumes on Europa has thus been confirmed, the origin of the plumes remains uncertain. Most notably, it is still unclear whether the inferred plumes are of oceanic origin, possibly containing information about the ocean's habitability, or if they are of surficial nature, offering information on the highly processed surface instead. In this study, we use a Monte-Carlo model to analyze three different plume models, two of which are surficial (near-surface liquid inclusion and diapir), and one of which originates in the sub-surface ocean (oceanic plume). We analyze all relevant Lyman- (Formula presented.) and OI 1304 (Formula presented.) emission mechanisms to determine the three models' emission profiles. These profiles are then compared to the Hubble Space Telescope/Space Telescope Imaging Spectograph measurements presented by Roth, Retherford, et al. (2014, https://doi.org/10.1073/pnas.1416671111) and Roth, Saur, et al. (2014, https://doi.org/10.1126/science.1247051) with the goal of determining which ab initio model fits these measurements best. Our analyses show that all three models investigated produce similar Lyman- (Formula presented.) and OI 130.4 nm emission profiles, with differences being perceivable only on scales well below the HST resolution and sensitivity. Since none of the models contradict the Roth, Retherford, et al. (2014, https://doi.org/10.1073/pnas.1416671111) and Roth, Saur, et al. (2014, https://doi.org/10.1126/science.1247051) observations, none of them can be ruled out as being the acting force behind the observed plumes. The currently available optical measurements are thus not sufficient to determine the physical nature of Europa's plumes, identification of which can only be achieved through higher resolution images or in situ measurements.

We have developed a new coronagraph using digital micromirror device (DMD) to observe faint emissions close to a bright objects in our solar system such as water plumes on Europa and Enceladus, plasma emissions in giant planet’s magnetospheres, escaping plasma and neutrals from Venus and Mars, and so on. The focal plane DMD mask enables us to occult planet’s disks and their moons even when their angular dimeter and geometry vary with time. The coronagraph composed of a DMD as an occulting mask on a telescope focal plane, a pupil stop, a narrow-band filter, and others. The DMD located at the focal plane produces color dispersion of entrance aperture on a pupil plane for an extended lightsource. Thus, we designed a proper shape of pupil mask to reduce remaining from the occulted light-source considering wavelength and bandwidth of observations. The coronagraph was installed on a Cassegrain focus of the Tohoku 60-cm telescope at Haleakala observatory in Hawaii. We have been using the coronagraph for observing sulfur ion emissions [SII] 671.6 and 673.1 nm from Io plasma torus since 2018. The DMD occultation reduces light from Jupiter disk and Galilean moons by 2.6×10-3. The system throughput is 56 % of a previous conventional coronagraph. In observation of Io plasma torus, north-south position of [SII] brightness peak shifted by 0.07 jovian radii toward the magnetic equator during three days. Increase of flesh pickup ion possibly makes higher anisotropy or higher ion perpendicular temperature causing the observed magnetic-equatorward shift of the plasma torus.

We describe the radiometric performance and ground calibration results of the JUpiter ICy moons Explorer Ultraviolet Spectrograph (JUICE-UVS) instrument. JUICE-UVS is a modest power (8 W) ultraviolet spectrograph that is the fifth in a series of Alice/UVS instruments built by Southwest Research Institute. JUICE-UVS covers a 50-204 nm bandpass with 0.4 nm spectral resolution over a 7.5° field of view with better than 0.3° spatial resolution. JUICE-UVS also features three different observing modes to allow higher-than-nominal spatial resolution observing as well as solar occultations in the Jupiter system. JUICE-UVS meets all performance requirements with margin, and is the first planetary UV spectrograph to feature a microchannel plate detector with an atomic layer deposition (ALD) coating to minimize in-flight gain loss due to accumulated fluence. JUICE-UVS also features both a time-tagged pixel list observing mode and a programmable histogram mode to maximize observational flexibility and data management. During the main JUICE mission, JUICE-UVS will explore the atmospheres and surfaces of the Galilean satellites, examine the dynamics of Jupiter’s upper atmosphere from pole to equator, and investigate the Jupiter-Io connection through observations of the Io torus.

Although mass and energy in Jupiter’s magnetosphere mostly come from the innermost Galilean moon Io’s volcanic activity, solar wind perturbations can play crucial roles in releasing the magnetosphe...

Europa is a Jupiter’s moon covered with a water-ice layer, hiding a global liquid water ocean approximately 100 km thick. Europa’s interior is heated by the tidal forces induced by Jupiter, that provide enough energy to maintain a vigorous geological activity on this moon. Europa’s surface is very young, with an age estimated around 70-90 Ma, which demonstrates a recent resurfacing of the moon. Various geological features have been identified at Europa’s surface, and some of them, like the smooth plains, domes and chaos might indicate the presence of sub-surface reservoirs of liquid water or brines (cryomagma). In this thesis, we propose a cryovolcanic eruption model from a cryomagma reservoir stored in the ice crust. The overpressure generated during the cryomagma freezing could be high enough to fracture the ice crust and let the cryolava rise toward the surface and spread on it. This predictive model allows us to know the duration of an eruption, and the total cryolava volume erupted as a function of the reservoir depth in the ice crust. It also allows us to calculate the pressure in the reservoir and the fluid velocity in the fracture during the eruption. We investigated the influence of the cryomagma composition and the ice crust rheology on the possibility of an eruption. We finally modeled the deformation of a reservoir stored in a viscoelastic ice crust. A few images taken by the Galileo spacecraft during the 1990’s show quasi-circular smooth features, that may be interpreted as cryolava flows. We wanted to use these images to constrain our eruption model by measuring the volume of these objects. To do this, we generated digital elevation models (DEMs) of these images thank to the photoclinometry technique. We used the AMES StereoPipeline (ASP) tool, provided by the NASA. We estimated the uncertainties on the DEMs produced by the ASP by doing a sensitivity study of this tool. We also measured the volume of four smooth plains and deduced the size of reservoir needed to generate these thanks to our eruption model. Two missions, JUICE (ESA) and Europa Clipper (NASA) will be launch in the next years and should provide new insights on Europa’s sub-surface. In this context, this thesis could help to select the zones the more likely to show biosignatures. The smooth plains studied in this thesis might be linking the interior and the surface of the Europa, which could present a great interest for the future exploration of this moon., Europe est une lune de Jupiter couverte de glace d’eau, et abritant un océan interne global d’eau liquide d’une centaine de kilomètres d’épaisseur. L’intérieur d’Europe est réchauffé par les forces de marées induites par la présence de Jupiter, qui fournissent une quantité d’énergie suffisante à maintenir une activité géologique vigoureuse sur ce satellite. La surface d’Europe est très jeune avec un âge estimé à 70-90 Ma, ce qui démontre son ressurfaçage récent. De nombreuses structures géologiques ont été identifiées à la surface d’Europe, et certaines comme les plaines lisses, les dômes ou les dépôts sombres pourraient indiquer la présence de réservoirs d’eau liquide ou de saumures (cryomagma) stockés dans la couche de glace. Nous proposons dans cette thèse un modèle d’éruption cryovolcanique depuis un réservoir de cryomagma contenu dans la couche de glaces. Le moteur de l’éruption est la surpression générée dans le réservoir par le gel du cryomagma, qui peut être suffisante pour entrainer la fracturation de la couche de glaces sus-jacente et laisser les cryolaves se répandre en surface. Ce modèle prédictif permet de connaître les caractéristiques d’une éruption telles que sa durée et le volume de cryolave émis en surface en fonction de la profondeur du réservoir. Il permet aussi d’évaluer la pression dans le réservoir et la vitesse du fluide s’en échappant au court de l’éruption. Nous avons testé l’influence de la composition du cryomagma et de la rhéologie de la couche de glace sur la faisabilité d’une éruption. Nous avons notamment modélisé la déformation d’un réservoir contenu dans une couche de glace viscoélastique. Quelques images d’Europe prises par la sonde Galileo dans les années 1990 montrent des structures lisses quasi-circulaires que nous interprétons comme de possibles écoulements de cryolaves à la surface. Nous avons souhaité utiliser le volume de ces objets afin de contraindre notre modèle d’éruption. Pour ce faire, nous avons généré des modèles numériques de terrain (MNT) de ces images grâce à la photoclinométrie, et plus particulièrement avec l’AMES StereoPipeline (ASP) fourni par la NASA. Nous avons porté une attention particulière à l’estimation des incertitudes sur les MNT en menant une étude de sensibilité de l’ASP. Nous avons pu mesurer le volume de quatre plaines lisses, et en déduire la taille des réservoirs de cryomagma requis pour les créer lors d’éruptions. Les missions JUICE (ESA) et Europa Clipper (NASA) devraient partir dans les prochaines années et permettront une étude plus poussée de la surface d’Europe. Cette thèse a pour vocation d’aider à la sélection des zones les plus susceptibles de présenter des bio-signatures en vue de ces missions. Les plaines lisses étudiées dans cette thèse peuvent possiblement représenter des zones d’échange d’eau liquide entre la surface et la sub-surface d’Europe, et sont donc d’un grand intérêt pour l’exploration future de cette lune.

The four larger satellites of Jupiter, with roughly comparable mass, are termed Galilean moons. They display (i) a water fraction that increases with dis- tance to Jupiter (ranging from no-water for volcanic innermost Io, to approximately half-half ratio of water and rocks for outermost Callisto) as well as (ii) various degrees of differentiation (two end-members corresponding to the two outer moons of similar radius: highly differentiated Ganymede, including a metallic core, locus of the dynamo observed at present, and much-less differentiated Callisto possibly harboring large volumes of ice-rock mixtures). A plausible cause for these variations can be related to the formation of the moons, although their later evolution could also affect both properties. Owing to the orbits of the four moons (compact, prograde, coplanar and nearly circular), a contemporaneous formation in a circum-jovian disk orbiting in the equatorial plane of the proto-planet is put forward, similar to the formation of planets albeit with significantly different time- and length-scales. The latter is not a minor difference: in practice, classical scenarios [1, 2] cope with the problem of too-much heating associated to large impacts as well as the migration of satellitesimals onto the proto-planet. A new paradigm for the formation of giant planets has emerged re- cently. It has been termed ’pebble accretion’ and highlights the efficiency of accretion of small particles in a context where gas drag dissipates energy as the pebble passes the protoplanet [3]. In this framework, formation of the Galilean moons is envisioned to occur naturally and contemporaneously to the growth of the giant planet. Details are nevertheless controversial: two re- cent scenarios propose either a fast [4] or a slow [5] accretion. Here, we reproduce these two end-member scenar- ios and specifically focus on the thermal evolution of the growing moons. A simple description of the heat equation is adopted assuming a spherical sym- metry. Heat deposition by pebbles as well as radiogenic heat sources are accounted for during a 30 Myr period that encompasses the formation of all moons. We systematically investigate the influence of timing (start/duration) and consider a range for the concentra- tion in of short-lived radio-isotopes (26Al,60Fe,53Mn) that reproduces the composition of LL (high enery content) and CI (low enery content) chondrites. Our results demonstrate that, whatever the scenario, the formation process involves little collisional energy, as can be expected owing to the small size of impactors. As a consequence, after 30 Myr of evolution, moons formed via pebble accretion show a small degree of differenciation or none at all. Either subsequent heat- ing via radioactive decay of long-lived isotopes or tidal heating possibly associated to the moons entrance in the Laplace resonance must be considered to explain the highly differentiated state observed at present for Ganymede. This includes the formation of the hydrosphere, the dehydration of rocks and the melting of the metallic component in order to form the moon’s core. Interestingly, the main heat sources differ depend- ing on the scenario: in the case of slow accretion, the decay of short-lived radio-isotopes is predominant when accretion of the moons starts sufficiently early; in the case of a fast accretion, the main heat source is associated to viscous dissipation in the disk that heats up the surface of the protosatellites. In the former case, the interior might reach the melting point of water in a limited fraction of the parameter space but only in the innermost region of the moons. Conversely, in the latter case, the melting point can be reached in the outer envelope, as predicted for large moons in the classical formation scenarios [6], but to a much lesser extent. The subsequent evolutionary path leading to the differentiation observed at present for Ganymede thus necessarily involve distinct dynami- cal phenomena: Rayleigh-Taylor type instabilities of the thick rock-ice mixture into the hydrosphere [7] if accretion is slow; if accretion is rapid, a possible delay in solid-state segregation of the rock component if double-diffusive convection occurs owing to a stabilizing density gradient [8]. [1] Estrada, P. R., Mosqueira, I., Lissauer, J. J., D’Angelo, G., and Cruikshank, D. P. (2009). Formation of Jupiter and conditions for accretion of the Galilean satellites. Eu- ropa, edited by RT Pappalardo, WB McKinnon, and K. Khurana, University of Arizona Press, Tucson, 27-58. [2] Canup, R. M., and Ward, W. R. (2009). Origin of Europa and the Galilean satellites. Europa, edited by RT Pappalardo, WB McKinnon, and K. Khurana, University of Arizona Press, Tucson, 59-83. [3] Johansen, A., and Lambrechts, M. (2017). Forming planets via pebble accretion. Annual Review of Earth and Planetary Sciences, 45, 359-387. [4] Ronnet,T., and Johansen,A.(2020). Formation of moon systems around giant planets-Capture and ablation of planetesimals as foundation for a pebble accretion scenario. Astronomy & Astrophysics, 633, A93. [5] Shibaike, Y., Ormel, C. W., Ida, S., Okuzumi, S., and Sasaki, T. (2019). The Galilean Satellites Formed Slowly from Pebbles. The Astrophysical Journal, 885(1), 79. [6] Monteux, J., Tobie, G., Choblet, G., and Le Feuvre, M. (2014). Can large icy moons accrete undifferentiated?. Icarus, 237, 377-387. [7] Rubin, M. E., Desch, S. J., and Neveu, M. (2014). The effect of Rayleigh-Taylor instabilities on the thickness of undifferentiated crust on Kuiper Belt Objects. Icarus, 236, 122-135. [8] O’Rourke, J. G., and Stevenson, D. J. (2014). Stability of ice/rock mixtures with application to a partially differentiated Titan. Icarus, 227, 67-77.

There is compelling evidence for subsurface water oceans among the three outer Galilean satellites, and evidence for an internal magma ocean in the innermost moon, Io. Tidal forces from Jupiter periodically deform these bodies, causing heating and deformation that, if measured, can probe their interior structures. In addition to Jupiter-raised tides, each moon also raises tides on the others. We investigate moon-moon tides for the first time in the Galilean moons, and show that they can cause significant heating through the excitation of high-frequency resonant tidal waves in their subsurface oceans. The heating occurs both in the crust and ocean, and can exceed that of other tidal sources and radiogenic decay if the ocean is inviscid enough. The resulting tidal deformation can be used to constrain subsurface ocean thickness. Our understanding of the thermal-orbital evolution and habitability of the Jovian system may be fundamentally altered as a result.