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Continuous observation of solar radio bursts (SRBs) throughout the year using the CALLISTO spectrometer generates a huge volume of spectral data. This study introduces a burst-classifier algorithm, which is an automated algorithm, to classify the SRB spectrum into three solar radio bursts, namely Type II (SRBT II), Type III (SRBT III) and Type IV (SRBT IV). The proposed algorithm was designed using four characteristic parameters derived from a collection of training dataset files. The characteristic parameters were derived from the intensity bursts observed on frequency channels and timesteps of the spectrum. This dataset consisted of 50 spectra of SRBT II and SRBT III, along with 40 spectra for SRBT IV, collected during the solar maximum of 2014 (Solar Cycle 24). After observations and analysis of the training dataset, each burst type was set up with a threshold. A training dataset of 80 data spectra from 2013 to 2016 was used to test the algorithm. Accuracy of the proposed algorithm was calculated using the percentage of true positives (TP) and false positives (FP). Findings demonstrate an accuracy of ∼74 % with 57 out of 80 spectra classified as TP and 23 spectra as FP. [ABSTRACT FROM AUTHOR]

Ganymede is the only known moon with an active dynamo. No mission has discovered intrinsic magnetism at the other Galilean satellites: Io, Europa, and Callisto. A dynamo requires a large magnetic Reynolds number, which in turn demands, for these moons, a large metallic core that is cooling fast enough for convection. Here we quantify these requirements to construct a regime diagram for the Galilean satellites. We compute the internal heat fluxes that would sustain a dynamo over the wide ranges of plausible radii for their metallic cores. Below a critical radius, no plausible heat flux will sustain a dynamo. Europa likely sits on the opposite side of this limit than Ganymede and Io. We predict that future missions may confirm a small (or absent) core, meaning that Europa could not sustain a dynamo even if its interior were cooling as quickly as Ganymede's core. Plain Language Summary: In the late 1990s, the NASA Galileo spacecraft visited the four largest moons of Jupiter: Io, Europa, Ganymede, and Callisto. Many studies interpret the Galileo gravity and magnetic field data to mean that: (a) Ganymede's intrinsic magnetic field arises from convection in a liquid metal core (i.e., a "dynamo" that converts mechanical energy into electromagnetic energy), (b) Europa has a metal core that is somehow incapable of generating a detectable magnetic field, and (c) Callisto may not have a metal core at all. Indeed, Ganymede is the only moon in our solar system known to sustain an active dynamo. Confirming the presence (or absence) of core convection provides us with valuable insight into the moons' structural and thermal history. In this study, we show that Europa's and Callisto's metal core (if they exist) may be too small to produce a dynamo, even if they convect. Crucially, no celestial body is known to have a convecting metal core without sustaining a dynamo too, but Europa might be an exception. Recently launched missions such as NASA's Europa Clipper and ESA's JUICE may test whether a small core size can explain the absence of dynamos at Europa and Callisto. Key Points: Dynamos in the Galilean moons would require both a dynamo‐producing region thicker than ∼250 km and core heat fluxes above ∼3 mW m−2Ganymede and Io probably have larger metallic cores than Europa and Callisto, but all satellites likely have similar core compositionsA small core could explain the absence of a strong dynamo at Europa even if Europa and Ganymede have similar core heat fluxes [ABSTRACT FROM AUTHOR]

Ovid's depiction of rape in the Metamorphoses has been interpreted as empathetic and proto-feminist at one extreme and pornographic at the other. In assessing this question, the current paper turns to trauma theory, a psychoanalytic methodology of growing popularity in the field of Classics, to demonstrate how Ovid depicts sexual violence and its aftermath with psychological acuity by emphasizing the mental, emotional, and physical experiences of rape survivors. I focus on the myth of Io, with parallels drawn to Daphne, Syrinx, Callisto, Proserpina, and Philomela. While cautiously supporting "optimistic" interpretations of the poem, this reading proves useful, regardless of authorial intent, in developing empathy-driven research and instruction in Classics courses and beyond. [ABSTRACT FROM AUTHOR]

The JUpiter ICy moons Explorer (JUICE) of ESA was launched on 14 April 2023 and will arrive at Jupiter and its moons in July 2031. In this review article, we describe how JUICE will investigate the interior of the three icy Galilean moons, Ganymede, Callisto and Europa, during its Jupiter orbital tour and the final orbital phase around Ganymede. Detailed geophysical observations about the interior of the moons can only be performed from close distances to the moons, and best estimates of signatures of the interior, such as an induced magnetic field, tides and rotation variations, and radar reflections, will be obtained during flybys of the moons with altitudes of about 1000 km or less and during the Ganymede orbital phase at an average altitude of 490 km. The 9-month long orbital phase around Ganymede, the first of its kind around another moon than our Moon, will allow an unprecedented and detailed insight into the moon's interior, from the central regions where a magnetic field is generated to the internal ocean and outer ice shell. Multiple flybys of Callisto will clarify the differences in evolution compared to Ganymede and will provide key constraints on the origin and evolution of the Jupiter system. JUICE will visit Europa only during two close flybys and the geophysical investigations will focus on selected areas of the ice shell. A prime goal of JUICE is the characterisation of the ice shell and ocean of the Galilean moons, and we here specifically emphasise the synergistic aspects of the different geophysical investigations, showing how different instruments will work together to probe the hydrosphere. We also describe how synergies between JUICE instruments will contribute to the assessment of the deep interior of the moons, their internal differentiation, dynamics and evolution. In situ measurements and remote sensing observations will support the geophysical instruments to achieve these goals, but will also, together with subsurface radar sounding, provide information about tectonics, potential plumes, and the composition of the surface, which will help understanding the composition of the interior, the structure of the ice shell, and exchange processes between ocean, ice and surface. Accurate tracking of the JUICE spacecraft all along the mission will strongly improve our knowledge of the changing orbital motions of the moons and will provide additional insight into the dissipative processes in the Jupiter system. Finally, we present an overview of how the geophysical investigations will be performed and describe the operational synergies and challenges. [ABSTRACT FROM AUTHOR]

This paper is devoted to some aspects of the study of relativistic effects (geodetic precession and geodetic nutation, which together constitute geodetic rotation) in the rotation of celestial bodies of the Solar System using the example of Jupiter and its Galilean satellites (Io, Europa, Ganymede, and Callisto). The difference in the angular velocity vectors of geodetic rotation is shown depending on the choice of reference frame. Thus, the absolute value of the angular velocity vector of the geodetic rotation of the satellite under study relative to the barycenter of the Solar System will not coincide with the absolute value of a similar vector of the satellite under study relative to the barycenter of the planet's satellite system. As a result, the most significant secular and periodic terms of geodetic rotation were determined for the first time: a) of Jupiter and its Galilean satellites in terms of the Euler angles, in the perturbing terms of physical libration and in the absolute value of the angular rotation vector of the geodetic rotation of the body under study relative to the barycenter of the Solar System and the plane of the mean orbit of Jupiter of the epoch J2000.0; b) of Galilean satellites of Jupiter in the perturbing terms of physical libration and the absolute value of the angular rotation vector of the geodetic rotation of the studied body relative to the barycenter of the Galilean satellite system of Jupiter and the mean orbit plane of the studied Galilean satellite of the epoch J2000.0. The obtained analytical values of the geodetic rotation of the studied objects can be used for a numerical study of their rotation in the relativistic approximation, and also used to evaluate the influence of relativistic effects on the orbital–rotational dynamics of bodies of exoplanetary systems. [ABSTRACT FROM AUTHOR]

Astrometric studies and orbital modelling of planetary moons have contributed significantly to advancing our understanding of their orbital dynamics. These studies require precise positions measured over extended periods. In this paper, we present the results of the 2021 Brazilian Jovian mutual phenomena campaign. The data correspond to eight events between Galilean satellites, in addition to a rare eclipse of Thebe, an inner satellite, totalling nine events. A geometric model along with the DE440/JUP365 ephemerides was used to reproduce the events and simulate the light curves. A Monte Carlo method and chi-squared statistics were used to fit the simulated light curves to the observations. The reflectance model adopted for our simulations was the complete version of the Oren–Nayer model. The average uncertainty of the relative positions of the Galilean satellites was 5 mas (15 km) and for the inner Thebe satellite 32 mas (96 km). The seven mutual events (nine independent observations) here analysed represent an addition of 17 per cent events (10 per cent light curves) with respect to the 2021 international mutual phenomena campaign. Furthermore, our result of Thebe eclipse is only the second measurement published to date. Our results contribute to the ephemeris data base, being fundamental to improving satellite orbits and thus minimizing their uncertainties. [ABSTRACT FROM AUTHOR]

Metric type II radio bursts are usually early indicators of CME-driven shocks and other space weather phenomena in the solar corona. This paper presents a detailed investigation of the spectral properties of band splitting type II radio bursts and their association with sunspot number. Using type II radio bursts in a frequency range [20 MHz–200 MHz] observed by CALLISTO during 2010–2017, it was discovered that the analyzed type II shock height, magnetic field strength, CME/shock speed, and Alfvén speed synchronize with the trajectory of the solar cycle 24. Also, the study revealed that the onset of the declining phase of solar cycle 24 has the highest electron density, whiles the frequency of type II bursts depicts a bimodal distribution during the study period, with peaks in 2012 and 2015. Further, a good correlation (with correlation factor R = 0.87) was obtained between the estimated CME/shock speeds from the dynamic spectra and the associated CME speeds from SOHO/LASCO. Moreover, the study confirmed a significant correlation (R= ∼0.8) between the absolute drift rates and the plasma frequency. Additionally, the study explored that ∼ 60% of the type II radio bursts considered in this study emanated from the western longitudes. Hence, the findings emphasize that the temporal dynamics of the physical conditions of band splitting type II radio bursts are essential parameters for space weather monitoring and forecasting. [ABSTRACT FROM AUTHOR]

To compare the efficacy of digital-assisted reference marking for toric implantable collamer lenses (Callisto Eye System) with manual marking technique using a slit lamp markeur. This study included patients that underwent implantation of a toric implantable collamer lens (EVO Visian toric ICL, Staar Surgical). Patients were included if they had a myopia above −3 diopters (D) and regular corneal astigmatism of 0.75 diopters or higher. Between both groups a 1:2 matching regarding similar preoperative level of myopia and astigmatism was performed. Visual and refractive outcomes were evaluated. Vector analysis was performed to evaluate total astigmatic changes. This study comprised 57 eyes of 57 patients with 19 eyes in the digital group and 38 eyes in the manual marking group. Postoperatively there were no statistically significant differences between both groups in UDVA (p = 0.467), spherical equivalent (SE) (p = 0.864), sphere (p = 0.761) and cylinder (p = 0.878). Vector analysis showed a slightly more accurate postoperative refractive astigmatism in the manual group (0.26 D at 107° ± 0.50 D) compared to the digital marking group (0.31 D at 107° ± 0.45 D), nevertheless with no statistically significant differences between both groups. A digital tracking approach for toric ICL alignment was an efficient and safe method for toric marking with similar results regarding visual and refractive outcomes compared to a conventional corneal marking method. Nevertheless, image-guided surgery helped to streamline the workflow in refractive ICL surgery. [ABSTRACT FROM AUTHOR]

The icy Galilean satellites are host to a broad range of impact feature morphologies. Hypotheses seeking to explain the diversity of these impact features consider the effects of impact melt, the physical state of the subsurface at the time of impact, and the impactor characteristics. As part of a larger effort to assess the role of these factors in the formation and evolution of these impact features, we have performed topographic and geological mapping of 19 large impact features on Ganymede and Callisto. These are divided into two main morphological groups: craters (subdivided into pit, dome, and anomalous dome craters), and penepalimpsests/palimpsests. The transitions from pit, dome, to anomalous dome craters appear to be size-dependent up to diameters of ∼170 km. The morphologies of pit and dome craters appear to be independent of their age or geologic context. The impacts that formed them only affected a cold, rigid ice layer, with the development of pits and raised annuli on their floors possibly stemming from the evolution of a pocket of impact melt. The subdued rims and floors of anomalous dome craters indicate the increasing effect of a weak, warm ice layer on impact feature morphology with increasing size, but their prominent annuli and pits indicate that mobilization of impact melt is also a factor. The very low topographic relief of older penepalimpsests and palimpsests indicates that their impacts penetrated the ice shell to mobilize very large volumes of pre-existing liquid from a subsurface layer, with little contribution to the final feature morphology from impact melt. Penepalimpsests are distinguished from palimpsests by the higher frequency of concentric ridges within their interiors, indicating a generally more robust state of the subsurface that could better support the rotation and uplift of solid material during impact, even if a crater-like depression could not be supported. A few impact features seem to be transitional between anomalous dome craters and penepalimpsests, and the overlap of anomalous dome craters, penepalimpsests, and palimpsests in terms of diameter as well as age indicates that impactor size and subsurface properties over time are major factors in determining which of these morphologies emerges. • Topographic and geologic maps made for 19 impact features on Ganymede and Callisto. • Generally young pit and dome craters formed by impact into a cold, rigid ice layer. • Evolution of a pocket of impact melt may produce the pits and surrounding annuli. • Impact penetration to a deeper, warm ice layer forms older anomalous dome craters. • Penetration of a subsurface liquid layer releases fluid forming ancient palimpsests. [ABSTRACT FROM AUTHOR]

The New Astrometric Reduction of Old Observations (NAROO) program is dedicated to the measurement of astrophotographic plates and the analysis of old observations for scientific purposes. One of the main objectives of the NAROO program is to provide accurate positional measurements of planets and satellites to improve our knowledge of their orbits and dynamics, and to infer the accuracy of the planet and satellite ephemerides. We digitized 553 astronegatives of the Galilean satellites taken with the McCormick 26-inch refractor in 1967/68 and the U.S. Naval Observatory 26-inch refractor from 1973 to 1998, resulting in 2650 individual observations. We measured and reduced these observations through an optimal process that includes image, instrumental, and spherical corrections using Gaia-DR3 catalog to provide the most accurate equatorial (RA, Dec) ICRS (Gaia-CRF3) positions. 4819 positions of the Galilean satellites have been determined with an accuracy of 55 mas (160 km at Jupiter), near the limit of the photographic technique for such work. These data can help to improve the equatorial positions of Jupiter. They also can be used in the context of quantifying tidal effects and will still be useful when Europa Clipper and Juice data will become available. • Analysis of USNO Galilean astro-photographic plates 1967–1998. • Photographic plate digitization at the NAROO center. • Limit of the astro-photographic technique. • Equatorial ICRS (Gaia-CRF3) positions of Jupiter, Io, Europa, Ganymede, Callisto. [ABSTRACT FROM AUTHOR]

Solar radio bursts are sudden peaks in the low-frequency radio emissions originating from the sun. These emissions, while revealing important insights into underlying physical mechanisms in solar physics, can also help predict space weather events that could have adverse effects on satellite communications and the global energy grid. A thorough understanding of this phenomena demands the collection and analysis of solar emission data over vast geographical and time scales. In this regard, the e-CALLISTO network plays a major role through having already archived more than 20 years worth of solar radio burst data. Leveraging on the advances in data analysis techniques, this data can be used to review the statistical significance of burst properties of type II and type III solar radio bursts and hence more importantly the magnetic field measurements of the active regions. In order to process the e-CALLISTO data, a software containing several data reduction processes is introduced to optimize the data analysis via a graphical user interface (GUI). The program is capable of reading out data from any CALLISTO receiving station, while offering visualization capabilities such as the color-corrected spectrum view, the plot of frequencies of the highest intensity, the individual frequency spectrum, the solar burst isolation portal, the fitting model for the radio burst, and the drift rate curve of the burst. These are achieved through using the raw "fits" files of spectra to perform background RFI reduction, identify and isolate solar radio burst regions, model the peak frequency variation using curve fitting, and thereby determine the frequency drift rates. The method can be directly applied to Type II and III solar bursts while providing space for tailoring and modification. In this work, the slow drift type II radio bursts were fitted by exponential decay and the fast drift type III radio bursts were approximated as linear decay. Hence, the frequency drift rates were computed for type II and type III radio bursts. The application is used to analyze several Type II and Type III solar radio bursts and depending on the bust type shock speed and electron velocity were determined. The GUI interface eliminates the time-consuming subjective manual analysis of e-CALLISTO data thereby making the analysis of solar radio bursts a routine and rapid process. • In this research a new software/python code has been introduced and tested for several Solar radio bursts data available in e-Callisto network. • Instead of finding the drift rates of solar radio bursts with image processing tools, analyzing intensity matrix of the solar radio bursts is used. • A new GUI is introduced for find the drift rates of the type II and type III solar radio bursts. • Using the new GUI, not only a graphical model can be illustrated for the bursts but some model statistics also can be obtained. [ABSTRACT FROM AUTHOR]

Geodetic and geophysical investigations of the Galilean moon Callisto address fundamental questions regarding the formation and evolution of the Jovian system. Callisto's evolution and internal structure appear to significantly differ from the other Jovian satellites. Similarly-sized Ganymede is a highly evolved ice-rock moon with a differentiated interior, intrinsic magnetic field, and abundant surface evidence of internal activity. In contrast, Callisto's surface is ancient, and Galileo spacecraft data suggest its interior is only incompletely differentiated, despite the presumed presence of a sub-surface ocean. These properties make Callisto uniquely able to constrain the timing and nature of the Jovian system formation. The Magnetics, Altimetry, Gravity, and Imaging of Callisto (MAGIC) mission concept is conceived to fully characterize the properties of this enigmatic moon from its deep interior to the icy shell. Three main instruments are included as a scientific payload. Highly accurate measurements of Callisto's topography, magnetic field, and morphology are obtained by the onboard laser altimeter, magnetometer, and camera, respectively. The telecommunication system supports an additional gravity and radio science investigation. Long- and short-wavelength gravity anomalies afford powerful constraints on internal differentiation and the properties of the hydrosphere (water and ice). Comprehensive numerical simulations and covariance analyses of MAGIC mission scenarios presented in this paper show that the gravitational degree-2 normalized coefficients and the pole obliquity enable the determination of the moment of inertia with an accuracy better than 0.015%. The combination of gravity and altimetry measurements acquired by MAGIC are essential to the characterization of Callisto's interior if – as is likely – the degree-2 gravity includes non-hydrostatic terms. MAGIC's radio science data yield the estimation of Callisto's gravity field with spatial resolutions of <100 km. The combination of gravitational and deformation tides that are retrieved by the radio science and altimetry investigations, respectively, leads to the recovery of the rigid ice shell thickness to within ∼3 km. Together these datasets would resolve ambiguities inherent in Galileo flyby data, revealing Callisto's interior structure as well as the existence and properties of its postulated internal ocean. • MAGIC is a medium-class mission concept to explore the Jovian moon Callisto. • The science payload is designed for a comprehensive geophysical investigation. • Highly accurate gravity measurements will be acquired from a low-altitude orbit. • A thorough estimation of Callisto's moment of inertia will reveal its interior. • Gravitational and deformation tides will help to constrain the ice/ocean properties. [ABSTRACT FROM AUTHOR]

The JUpiter ICy moons Explorer (JUICE) of the European Space Agency will investigate Jupiter and its icy moons Europa, Ganymede, and Callisto, with the aim to better understand the origin and evolution of our Solar System and the emergence of habitable worlds around gas giants. The Particle Environment Package (PEP) on board JUICE is designed to measure neutrals and ions and electrons at thermal, suprathermal, and radiation belt energies (eV to MeV). In the vicinity of Callisto, PEP will characterize the plasma environment, the outer parts of Callisto's atmosphere and ionosphere and their interaction with Jupiter's dynamic magnetosphere. Roughly 20 Callisto flybys with closest approaches between 200 and 5,000 km altitude are planned over the course of the JUICE mission. In this article, we review the state of the art regarding Callisto's ambient environment and magnetospheric interaction with recent modeling efforts for Callisto's atmosphere and ionosphere. Based on this review, we identify science opportunities for the PEP observations to optimize scientific insight gained from the foreseen JUICE flybys. These considerations will inform both science operation planning of PEP and JUICE and they will guide future model development for Callisto's atmosphere, ionosphere, and their interaction with the plasma environment. Key Points: Particle Environment Package (PEP) on JUpiter ICy moons Explorer (JUICE) will provide in situ and remote measurements of Callisto's atmosphere and its space environment during ∼20 flybysWe investigate operation plans and instrument capabilities to optimize science return from PEP observationsThe interactions of the atmosphere with the space environment and surface are complex and must be further analyzed in preparation for JUICE [ABSTRACT FROM AUTHOR]

A growing number of satellites in the outer solar system likely have global oceans beneath their outer icy shells. While the presence of liquid water makes these ocean worlds compelling astrobiological targets, the exchange of heat and materials between the deep interior and the surface also plays a critical role in promoting habitable environments. In this article, we combine geophysical, geochemical, and geological observations of the Jovian satellites Europa, Ganymede, and Callisto as well as the Saturnian satellites Enceladus and Titan to summarize our current state of understanding of their interiors and surface exchange processes. Potential mechanisms for driving exchange processes upward from the ocean floor and downward from the satellite surface are then reviewed, which are primarily based on numerical models of ice shell and ocean dynamics and complemented by terrestrial analog studies. Future missions to explore these exo-oceans will further revolutionize our understanding of ice-ocean exchange processes and their implications for the habitability of these worlds. [ABSTRACT FROM AUTHOR]

The study of the Galilean satellites can help clarify the structure of the magnetospheric magnetic field from observations of their projections along magnetic field lines in the atmosphere/ionosphere of Jupiter, where patches of auroras appear. UV auroras in projections on the ionosphere of Io, Europe and Ganymede occur almost permanently, while the observation of the track of Callisto is difficult. One of the reasons is that the Callisto projection lies near or inside Jupiter's bright main oval. Another reason is that Callisto is not constantly in the sub-Alfvenic flow of magnetospheric plasma. The interaction of Callisto with the magnetospheric plasma of the planet is an actual problem widely discussed in the literature, which sheds light on the key processes occurring in the Jovian system. [ABSTRACT FROM AUTHOR]

Pressures in the hydrospheres of large ocean worlds extend to ranges exceeding those in Earth deepest oceans. In this regime, dense water ices and other high-pressure phases become thermodynamically stable and can influence planetary processes at a global scale. The presence of high-pressure ices sets large icy worlds apart from other smaller water-rich worlds and complicates their study. Here we provide an overview of the unique physical states, thermodynamics, dynamic regimes, and evolution scenarios specific to large ocean worlds where high-pressure ice polymorphs form. We start by (i) describing the current state of knowledge for the interior states of large icy worlds in our solar system (i.e. Ganymede, Titan and Callisto). Then we (ii) discuss the thermodynamic and physical specifics of the relevant high–pressure materials, including ices, aqueous fluids and hydrates. While doing this we (iii) describe the current state of the art in modeling and understanding the dynamic regimes of high-pressure ice mantles. Based on these considerations we (iv) explore the different evolution scenarios for large icy worlds in our solar system. We (v) conclude by discussing the implications of what we know on chemical transport from the silicate core, extrapolation to exoplanetary candidate ocean worlds, limitations to habitability, differentiation diversity, and perspectives for future space exploration missions and experimental measurements. [ABSTRACT FROM AUTHOR]

Zusammenfassung Seit 40 Jahren erforschen Sonden die Eismonde im äußeren Sonnensystem. Die Vielfalt dieser Körper, die mögliche Existenz von verborgenen Ozeanen und ihr Kryovulkanismus machen sie zu äußerst spannenden Himmelskörpern. Teil 1 dieses Zweiteilers stellt die Eismonde von Jupiter und Saturn vor. Jeder dieser Eismonde zeigt sich geologisch als eigene Welt. Bei den Jupitertrabanten ist die Oberfläche von Europa im Vergleich zu Ganymed geologisch sehr jung. Magnetfeldmessungen der Galileo‐Mission lassen unter der festen Eiskruste auf einen tiefen Ozean mit salzhaltigem Wasser schließen. Ein solcher Ozean existiert ebenfalls auf Callisto in größerer Tiefe, mutmaßlich auch auf Ganymed. Ganymed besitzt als einziger Eismond einen eisenhaltigen Kern, dessen starkes Magnetfeld das eines Ozeans überdeckt. Der Saturnmond Enceladus zeichnet sich durch aktiven Kryovulkanismus aus, der durch Gezeitenkräfte angetrieben ist. [ABSTRACT FROM AUTHOR]

Sulphur dioxide (SO 2) is known to be present on Callisto. In this paper, we studied the chemical evolution of SO 2 astrochemical ice induced by irradiation using 9 eV (137.7 nm) vacuum ultraviolet light produced from the high-flux beamline of the storage ring at the National Synchrotron Radiation Research Centre in Taiwan. Ultraviolet absorption spectra of the irradiated ice recorded in the 240–320 nm region reveal a broad absorption band indicating the formation of ozone. By comparing these laboratory spectra with Hubble Space Telescope data of the surface of Callisto in this spectral region, we find compelling evidence to consider the presence of ozone on Callisto. Furthermore, there is an additional band peaking at 309 nm whose assignment is as yet unclear but is quite similar to a band observed on Ganymede, thus leading us to suspect a common molecular source. • 9 eV photo irradiation of Sulphur dioxide (SO 2) under astrochemical icy condition. • Vacuum ultraviolet spectra of pre- and post-irradiation Sulphur dioxide (SO 2) at 9 K. • Additional absorption and shift in the peak position (281 nm to 265 nm) ascribed to Hartley absorption band of ozone (O 3). • Shift in peak position when warmed to 100 K is due to sublimation of O 3 except the trapped O 3 in SO 2 ice. • Comparison of the UV spectra from HST and present experiment provides concrete evidence for presence of Ozone on Callisto. [ABSTRACT FROM AUTHOR]

Complex craters with diameters (D) ≥ 40 km on Callisto and Ganymede are shallower than would be expected from simply extrapolating the depth-diameter trend from smaller (D ≤ 40 km) craters. This unusual depth-diameter (d-D) trend, and associated changes in crater morphology, have been hypothesized to result from rheological transitions, including the existence of an ocean, within the moons' ice shell. Simulations of impact crater formation can reproduce the observed shallow depths but require heat fluxes roughly twice the maximum radiogenic flux to do so. Here we demonstrate that the d-D trends on Callisto and Ganymede can instead be explained as a direct consequence of viscous relaxation under radiogenic heating. We use numerical simulations of viscous relaxation to show that if craters form at the depth expected from an extrapolation of the complex crater d-D trend, they will evolve to the observed depths over timescales of 200 Myrs to 1 Gyrs. Large craters (e.g., D ≥ 80 km) younger than 200 Myrs, which would retain greater depths, should be relatively rare. If we instead assume that the craters formed at their observed depths, as proposed by previous impact modeling, they quickly become much shallower than observed. We find excellent agreement between observed crater depths on Ganymede and our simulated crater depths by assuming a pure-water ice composition and a diurnally averaged surface temperature of 120 K, but require either larger-grained or "dirty" ice with a modestly higher viscosity to match observations at Callisto, where the surface temperature is warmer (130 K). We favor the latter explanation because it is consistent with the existence of a dusty lag on Callisto's surface and the absence of a similar lag on Ganymede. Our results predict that, for a given crater diameter, post-relaxation crater depth should increase with increasing latitude, a hypothesis best tested on Callisto, whose relatively quiescent geologic history best preserves the signature of viscous relaxation under radiogenic heating. • Large, fresh craters on Callisto and Ganymede are observed to be unusually shallow. • We show that radiogenic heat causes rapid viscous relaxation of large craters. • Simulated depths match observations if craters are 200 Myrs to 1 Gyrs old. • Callisto's warmer crust is likely a mix of ice and dust to retard relaxation. [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]

The Aalto University Metsähovi Radio Observatory (MRO) in Finland installed and started operating a new low‐frequency solar radio monitoring instrument in October 2017. The main component of the new system is a crossed dipole antenna, and it uses a Callisto spectrometer as the back‐end. The operational range of the new radio telescope is between 5 and 120 MHz, and its main purpose is to detect solar radio bursts. The coverage of MRO solar radio observations now extends from 5 MHz to 37 GHz, enabling studies of solar flares over a very wide frequency range. The first solar radio bursts were detected with the new system in March 2018. In this article, we describe the new system and report the first flare observations. [ABSTRACT FROM AUTHOR]

Robotic exploration of the Solar System revealed one planet, moon, or small body after another as unique geologic worlds. Simultaneously, photometric modeling arose as a complementary field that described both the macroscopic and microscopic features of the surface, including roughness (often at scales below the resolution limit of instruments), compaction states, and the sizes of particles comprising the upper regolith. This "hypervision" positioned photometric analysis with an uncanny ability to claim priority in a number of foundational discoveries, including the prediction that Uranus possessed a family of outer irregular moons, that Titan possessed two major categories of landforms defined by their roughness, that Enceladus was geologically active, that seasonal volatile transport was occurring in the outer Solar System, and that the low-albedo side of Iapetus was exogenously placed. Hints of discoveries yet to come include active cryovolcanism on Europa, a geologically active (136199) Eris, and a small or non-existent northern polar cap on Triton. • Photometric studies represent a powerful tool for deriving the physical properties of surfaces. • Photometry often presents the first indication of geologic activity or the presence of undiscovered objects. • Photometric modeling can "see" below the spatial resolution limit of spacecraft instruments. [ABSTRACT FROM AUTHOR]

While the existence of a buried ocean sandwiched between surface ice and high-pressure (HP) polymorphs of ice emerges as the most plausible structure for the hundreds-of-kilometers thick hydrospheres within large icy moons of the Solar System (Ganymede, Callisto, Titan), little is known about the thermal structure of the deep HP ice mantle and its dynamics, possibly involving melt production and extraction. This has major implications for the thermal history of these objects as well as on the habitability of their ocean as the HP ice mantle is presumed to limit chemical transport from the rock component to the ocean. Here, we describe 3D spherical simulations of subsolidus thermal convection tailored to the specific structure of the HP ice mantle of large icy moons. Melt production is monitored and melt transport is simplified by assuming instantaneous extraction to the ocean above. The two controlling parameters for these models are the rheology of ice VI and the heat flux from the rock core. Reasonable end-members are considered for both parameters as disagreement remains on the former (especially the pressure effect on viscosity) and as the latter is expected to vary significantly during the moon’s history. We show that the heat power produced by radioactive decay within the rock core is mainly transported through the HP ice mantle by melt extraction to the ocean, with most of the melt produced directly above the rock/water interface. While the average temperature in the bulk of the HP ice mantle is always relatively cool when compared to the value at the interface with the rock core (∼ 5 K above the value at the surface of the HP ice mantle), maximum temperatures at all depths are close to the melting point, often leading to the interconnection of a melt path via hot convective plume conduits throughout the HP ice mantle. Overall, we predict long periods of time during these moons’ history where water generated in contact with the rock core is transported to the above ocean. [ABSTRACT FROM AUTHOR]

Radar probing of Jovian icy satellites is fundamental for understanding the moons' origin and their thermal evolution as potential habitable environments in our Solar System. Using the current state of knowledge of the geological and geophysical properties of Ganymede, Europa and Callisto, we perform a comprehensive radar detectability study to quantify the exploration depth and the lower limit for subsurface identification of water and key tectonic structural elements. To achieve these objectives, we establish parametric dielectric models that reflect different hypotheses on the formation and thermal evolution of each moon. The models are then used for FDTD radar propagation simulations at the 9-MHz sounding frequency proposed for both ESA JUICE and NASA Europa missions. We investigate the detectability above the galactic noise level of four predominant subsurface features: brittle-ductile interfaces, shallow faults, brine aquifers, and the hypothesized global oceans. For Ganymede, our results suggest that the brittle-ductile interface could be within radar detectability range in the bright terrains, but is more challenging for the dark terrains. Moreover, understanding the slope variation of the brittle-ductile interface is possible after clutter reduction and focusing. For Europa, the detection of shallow subsurface structural elements few kilometers deep (such as fractures, faults and brine lenses) is achievable and not compromised by surface clutter. The objective of detecting the potential deep global ocean on Europa is also doable under both the convective and conductive hypotheses. Finally, for Callisto, radar waves can achieve an average penetration depth of ∼15 km, although the current understanding of Callisto's subsurface dielectric properties does not suggest sufficiently strong contrasts to produce unambiguous radar returns. [ABSTRACT FROM AUTHOR]

We develop a model of the ionospheric electron population of Jupiter’s moon Callisto using a prescribed neutral atmosphere composed of O 2 , CO 2 and H 2 O. A kinetic description of ionospheric suprathermal electrons coupled with a fluid description of ionospheric thermal electrons is well suited to jointly analyze and interpret observations of electron density and atmospheric UV emission. Accordingly, we calculate the electron energy distribution function at each point in the ionosphere by solving a coupled set of equations consisting of the Boltzmann equation for suprathermal electrons and the continuity and energy equation for thermal electrons. We assume a stationary balance between local sources and sinks of electrons and electron energy. Electron transport within the ionosphere is neglected, since collision time scales are shorter than transport time scales in the region of Callisto’s ionosphere where the major concentrations of electrons is located and the major part of the atmospheric UV emission is generated. We consider photoionization, which is the dominant ionospheric electron source, and secondary ionization from collisions of photoelectrons with neutrals. Our calculations yield electron densities and electron impact generated UV emissions from Callisto’s atmosphere. Comparing our modeled UV emission intensities with the Hubble Space Telescope observation of Cunningham et al. (2015) , we find that Callisto’s atmosphere has a mean O 2 column density of 2 . 1 − 1.1 + 1.1 × 10 19 m − 2 . A joint comparison with this HST observation and radio occultation observations of Kliore et al. (2002) shows that Callisto’s atmosphere possesses a day night asymmetry. We derive terminator O 2 column densities of ∼ 0.4 × 10 19 m − 2 , for which we find subsolar O 2 column densities in the range of 2.4 − 9.8 × 10 19 m − 2 . Our calculations also show that the electron density is very sensitive to the relative abundance of H 2 O due to the thermal electron cooling by rotational state excitation of H 2 O. For the efficiency of Callisto’s atmospheric UV emission we find that on average one photon is emitted at OI λ 135.6 nm per every 170 electron ion pairs generated and per every 60 electron ion pairs produced by secondary electron impact ionization. [ABSTRACT FROM AUTHOR]

We model Callisto’s exosphere based on its ice as well as non-ice surface via the use of a Monte-Carlo exosphere model. For the ice component we implement two putative compositions that have been computed from two possible extreme formation scenarios of the satellite. One composition represents the oxidizing state and is based on the assumption that the building blocks of Callisto were formed in the protosolar nebula and the other represents the reducing state of the gas, based on the assumption that the satellite accreted from solids condensed in the jovian sub-nebula. For the non-ice component we implemented the compositions of typical CI as well as L type chondrites. Both chondrite types have been suggested to represent Callisto’s non-ice composition best. As release processes we consider surface sublimation, ion sputtering and photon-stimulated desorption. Particles are followed on their individual trajectories until they either escape Callisto’s gravitational attraction, return to the surface, are ionized, or are fragmented. Our density profiles show that whereas the sublimated species dominate close to the surface on the sun-lit side, their density profiles (with the exception of H and H 2 ) decrease much more rapidly than the sputtered particles. The Neutral gas and Ion Mass (NIM) spectrometer, which is part of the Particle Environment Package (PEP), will investigate Callisto’s exosphere during the JUICE mission. Our simulations show that NIM will be able to detect sublimated and sputtered particles from both the ice and non-ice surface. NIM’s measured chemical composition will allow us to distinguish between different formation scenarios. [ABSTRACT FROM AUTHOR]

We report the result of a search for evidence of an O 2 -dominated atmosphere on Callisto, using the high far-ultraviolet sensitivity of the Hubble Space Telescope Cosmic Origins Spectrograph (COS). Observations of Callisto’s leading/Jupiter-facing hemisphere show, for the first time, variable-strength atomic oxygen (O I) emissions with brightness up to 4.7 ± 0.7 Rayleighs for the O I 1304 Å triplet and 1.9 ± 0.4 Rayleighs for the O I 1356 Å doublet, averaged over the 2.5 arcsec. diameter COS aperture. Because the observations were made in Earth’s shadow, and are brighter than expected emission from nighttime geocoronal airglow or other plausible sources, we are confident that they originate from Callisto or its immediate vicinity. In addition, COS’s limited (∼1 arcsec) spatial resolution implies a 2 σ detection of excess 1356 Å emission concentrated on the disk of Callisto itself, with brightness 3.2 ± 1.6 Rayleighs. The (O I 1356 Å)/(O I 1304 Å) emission ratio from Callisto’s disk favors dissociative excitation of O 2 , suggesting that O 2 is the dominant atmospheric component rather than other possible oxygen-bearing alternatives. Photoelectrons, rather than magnetospheric electrons, are the most likely source of the dissociative excitation. This detection yields an O 2 column density of ∼4 × 10 15 cm −2 on the leading/Jupiter facing hemisphere, which implies that Callisto’s atmosphere is collisional and is the fourth-densest satellite atmosphere in the Solar System, in addition to being the second-densest O 2 -rich collisional atmosphere in the Solar System, after Earth. Longitudinal variations in published densities of ionospheric electrons suggest that O 2 densities in Callisto’s trailing hemisphere, which we did not observe, may be an order of magnitude greater. The aperture-filling emissions imply that there is also an extended corona of predominantly O I 1304 Å emission around Callisto, with observed strength of 1–4 Rayleighs, likely due to solar resonance scattering from sputtered atomic O, with a density of up to 10 4 cm −3 at the exobase. [ABSTRACT FROM AUTHOR]

Highlights: [•] We study the properties of the Slichter modes of large icy satellites. [•] The periods are of the order of a few hours and depend mainly on the ocean thickness. [•] Ganymede has two Slichter modes due to the presence of two global liquid layers. [•] We study the possible observation and excitation of these modes by an impact. [Copyright &y& Elsevier]

Highlights: [•] We test the validity of the Radau–Darwin Approximation (RDA) on icy satellites. [•] The RDA is valid to within 99% for hydrostatic solid bodies in the Solar System. [•] Nonhydrostaticity leads to errors in moment of inertia and deviatoric stress. [•] Slow rotators are more affected by nonhydrostaticity for a given stress. [•] Current data does not rule out a fully differentiated Titan or Callisto. [Copyright &y& Elsevier]

Highlights: [•] We study the effects of elastic tidal deformation on the librations of icy satellites. [•] Libration amplitudes are calculated for the icy Galilean satellites and Titan. [•] Elastic effects on libration are on the order of a few percent for solid satellites. [•] Elastic deformation strongly reduces the potential amplifying effect of an ocean. [•] Length-of-day variations of Titan are substantially amplified by elastic effects. [Copyright &y& Elsevier]

Abstract: Past exploration of Jupiter''s diverse satellite system has forever changed our understanding of the unique environments to be found around gas giants, both in our solar system and beyond. The detailed investigation of three of Jupiter''s Galilean satellites (Ganymede, Europa, and Callisto), which are believed to harbour subsurface water oceans, is central to elucidating the conditions for habitability of icy worlds in planetary systems in general. The study of the Jupiter system and the possible existence of habitable environments offer the best opportunity for understanding the origins and formation of the gas giants and their satellite systems. The JUpiter ICy moons Explorer (JUICE) mission, selected by ESA in May 2012 to be the first large mission within the Cosmic Vision Program 2015–2025, will perform detailed investigations of Jupiter and its system in all their inter-relations and complexity with particular emphasis on Ganymede as a planetary body and potential habitat. The investigations of the neighbouring moons, Europa and Callisto, will complete a comparative picture of the Galilean moons and their potential habitability. Here we describe the scientific motivation for this exciting new European-led exploration of the Jupiter system in the context of our current knowledge and future aspirations for exploration, and the paradigm it will bring in the study of giant (exo) planets in general. [Copyright &y& Elsevier]

Abstract: Irregular satellites are dormant comet-like bodies that reside on distant prograde and retrograde orbits around the giant planets. They are likely to be captured objects. Dynamical modeling work indicates they may have been caught during a violent reshuffling of the giant planets ∼4Gy ago (Ga) as described by the so-called Nice model. According to this scenario, giant planet migration scattered tens of Earth masses of comet-like bodies throughout the Solar System, with some comets finding themselves near giant planets experiencing mutual encounters. In these cases, gravitational perturbations between the giant planets were often sufficient to capture the comet-like bodies onto irregular satellite-like orbits via three-body reactions. Modeling work suggests these events led to the capture of on the order of ∼0.001 lunar masses of comet-like objects on isotropic orbits around the giant planets. Roughly half of the population was readily lost by interactions with the Kozai resonance. The remaining half found themselves on orbits consistent with the known irregular satellites. From there, the bodies experienced substantial collisional evolution, enough to grind themselves down to their current low-mass states. Here we explore the fate of the putative irregular satellite debris in the Jupiter system. Pulverized by collisions, we hypothesize that the carbonaceous chondrite-like material was beaten into small enough particles that it could be driven toward Jupiter by Poynting–Robertson (P–R) drag forces. Assuming its mass distribution was dominated by D >50μm particles, we find that >40% ended up striking the Galilean satellites. The majority were swept up by Callisto, with a factor of 3–4 and 20–30 fewer particles reaching Ganymede and Europa/Io, respectively. Collision evolution models indicate most of this material arrived about 4Ga, but some is still arriving today. We predict that Callisto, Ganymede, Europa, and Io were buried about 4Ga by ∼120–140m, 25–30m, 7–15m, and 7–8m of dark debris, respectively. The first two values are consistent with observations of the deepest dark lag deposits found on the most ancient terrains of Callisto and Ganymede. The rest of the debris was likely worked into the crusts of these worlds by geologic and impact processes. This suggests the debris is a plausible source of the dark lag material found in Europa’s low-lying crevices. More speculatively, it is conceivable that the accreted dark particles were a significant source of organic material to Europa’s subsurface ocean. [Copyright &y& Elsevier]

Abstract: The discovery of volcanic activity on Enceladus stands out amongst the long list of findings by the Cassini mission to Saturn. In particular the compositional analysis of Enceladus ice particles by Cassini''s Cosmic Dust Analyser (CDA) () has proven to be a powerful technique for obtaining information about processes below the moon''s ice crust. Small amounts of sodium salts embedded in the particles'' ice matrices provide direct evidence for a subsurface liquid water reservoir, which is, or has been, in contact with the moon''s rocky core (). Jupiter''s Galilean satellites Ganymede, Europa, and Callisto are also believed to have subsurface oceans and are therefore prime targets for future NASA and ESA outer Solar System missions. The Galilean moons are engulfed in tenuous dust clouds consisting of tiny pieces of the moons'' surfaces (), released by hypervelocity impacts of micrometeoroids, which steadily bombard the surfaces of the moons. In situ chemical analysis of these grains by a high resolution dust spectrometer will provide spatially resolved mapping of the surface composition of Europa, Ganymede, and Callisto, meeting key scientific objectives of the planned missions. However, novel high-resolution reflectron-type dust mass spectrometers () developed for dust astronomy missions () are probably not robust enough to be operated in the energetic radiation environment of the inner Jovian system. In contrast, CDA''s linear spectrometer is much less affected by harsh radiation conditions because its ion detector is not directly facing out into space. The instrument has been continuously operated on Cassini for 11 years. In this paper we investigate the possibility of operating a CDA-like instrument as a high resolution impact mass spectrometer. We show that such an instrument is capable of reliably identifying traces of organic and inorganic materials in the ice matrix of ejecta expected to be generated from the surfaces of the Galilean moons. These measurements are complementary, and in some cases superior, compared to other traditional techniques such as infrared remote sensing or in situ ion or neutral mass spectrometers. [Copyright &y& Elsevier]

Abstract: Mesotrione is a benzoylcyclohexane-1,3-dione herbicide that inhibits 4-hydroxyphenyl pyruvate dioxygenase in target plants. Although it has been used since 2000, only a limited number of degrading microorganisms have been reported. Mesotrione-degrading bacteria were selected among strains isolated from Brazilian aquatic environments, located near corn fields treated with this herbicide. Pantoea ananatis was found to rapidly and completely degrade mesotrione. Mesotrione did not serve as a sole C, N, or S source for growth of P. ananatis, and mesotrione catabolism required glucose supplementation to minimal media. LC–MS/MS analyses indicated that mesotrione degradation produced intermediates other than 2-amino-4-methylsulfonyl benzoic acid or 4-methylsulfonyl-2-nitrobenzoic acid, two metabolites previously identified in a mesotrione-degrading Bacillus strain. Since P. ananatis rapidly degraded mesotrione, this strain might be useful for bioremediation purposes. [Copyright &y& Elsevier]

Abstract: Previous analyses of Galileo images showed the small (≈1km and smaller) crater population on Callisto to be lower than had been expected (Moore, J.M. et al. [1999]. Icarus 140, 294–312; Bierhaus E.B. et al. [2000]. Lunar Planet. Sci. 31. Abstract #1996). In this paper we examine the small crater population using high-resolution imagery from Callisto flybys during Galileo orbits C3, C10, C21, and C30, including several C30 regions not previously analyzed. Our findings confirm that most small craters are depleted relative to a presumed equilibrium of R =0.22, and we find that there is significant variability in the small crater counts. While some of the variability in the small crater population on Callisto can be attributed to secondary cratering, some variability also may be explained by resetting of portions of Callisto’s surface by larger impactors. This is expected where the differential size frequency distribution of the crater production population b <3 (where b represents the exponent of a differential power-law crater-size distribution), such that large impacts affect a greater planetary surface area than smaller craters. [Copyright &y& Elsevier]

Abstract: Missions to explore Europa have been imagined ever since the Voyager mission first suggested that Europa was geologically very young. Subsequently, the Galileo spacecraft supplied fascinating new insights into this satellite of Jupiter. Now, an international team is proposing a return to the Jupiter system and Europa with the Europa Jupiter System Mission (EJSM). Currently, NASA and ESA are designing two orbiters that would explore the Jovian system and then each would settle into orbit around one of Jupiter’s icy satellites, Europa and Ganymede. In addition, the Japanese Aerospace eXploration Agency (JAXA) is considering a Jupiter magnetospheric orbiter and the Russian Space Agency is investigating a Europa lander. The Jupiter Europa Orbiter (JEO) would be the NASA-led portion of the EJSM; JEO would address a very important subset of the complete EJSM science objectives and is designed to function alone or in conjunction with ESA’s Jupiter Ganymede Orbiter (JGO). The JEO mission concept uses a single orbiter flight system that would travel to Jupiter by means of a multiple-gravity-assist trajectory and then perform a multi-year study of Europa and the Jupiter system, including 30months of Jupiter system science and a comprehensive Europa orbit phase of 9months. The JEO mission would investigate various options for future surface landings. The JEO mission science objectives, as defined by the international EJSM Science Definition Team, include: [A.] Europa’s ocean: Characterize the extent of the ocean and its relation to the deeper interior. [B.] Europa’s ice shell: Characterize the ice shell and any subsurface water, including their heterogeneity, and the nature of surface–ice–ocean exchange. [C.] Europa’s chemistry: Determine global surface compositions and chemistry, especially as related to habitability. [D.] Europa’s geology: Understand the formation of surface features, including sites of recent or current activity, and identify and characterize candidate sites for future in situ exploration. [E.] Jupiter system: Understand Europa in the context of the Jupiter system. The JEO orbital mission would provide critical measurements to support the scientific and technical selection of future landed options. The primary challenge of a Europa mission is to perform in Jupiter’s radiation environment, radiation damage being the life-limiting parameter for the flight system. Instilling a system-level radiation-hardened-by-design approach very early in the mission concept would mitigate the pervasive mission and system-level impacts (including trajectory, configuration, fault protection, operational scenarios, and circuit design) that can otherwise result in runaway growth of cost and mass. This paper addresses the JEO mission concept developed by a joint team from JPL and the Applied Physics Laboratory to address the science objectives defined by an international science definition team formed in 2008, while designing for the Jupiter environment. [Copyright &y& Elsevier]

Abstract: Impact craters on icy satellites display a wide range of morphologies, some of which have no counterpart on rocky bodies. Numerical simulation studies have struggled to reproduce the diversity of features, such as central pits and transitions in crater depth with increasing diameter, observed on the icy Galilean satellites. The transitions in crater depth (at diameters of about 26 and 150km on Ganymede and Callisto) have been interpreted as reflecting subsurface structure. Using the CTH shock physics code, we model the formation of craters with diameters between 400m and about 200km on Ganymede using different subsurface temperature profiles. Our calculations include recent improvements in the model equation of state for H2O and quasi-static strength parameters for ice. We find that the shock-induced formation of dense high-pressure polymorphs (ices VI and VII) creates a gap in the crater excavation flow, which we call discontinuous excavation. For craters larger than about 20km, discontinuous excavation concentrates a hot plug of material (>270K and mostly on the melting curve) in the center of the crater floor. The size and occurrence of the hot plug are in good agreement with the observed characteristics of central pit craters, and we propose that a genetic link exists between them. We also derive depth versus diameter curves for different internal temperature profiles. In a 120K isothermal crust, calculated craters larger than about 30km diameter are deeper than observed and do not reproduce the transition at about 26km diameter. Calculated crater depths are shallower and in good agreement with observations between about 30 and 150km diameter using a warm thermal gradient representing a convective interior. Hence, the depth-to-diameter transition at about 26km reflects thermal weakening of ice. Finally, simulation results generally support the hypothesis that the anomalous interior morphologies for craters larger than 100km are related to the presence of a subsurface ocean. [Copyright &y& Elsevier]

Abstract: Astrometric satellite positions are derived from timings of their eclipses in the shadow of Jupiter. The 548 data points span 20years and are accurate to about 0.006arcsec for Io and Europa and about 0.015arcsec or better for Ganymede and Callisto. The precision of the data set and its nearly continuous distribution in time allows measurement of regular oscillations with an accuracy of 0.001arcsec. This level of sensitivity permits detailed evaluation of modern ephemerides and reveals anomalies at the 1.3year period of the resonant perturbations between Io, Europa and Ganymede. The E5 ephemeris shows large errors at that period for all three satellites as well as other significant anomalies. The L1 ephemeris fits the observations much more closely than E5 but discrepancies for the resonant satellites are still apparent and the measured positions of Io are drifting away from the predictions. The JUP230 ephemeris fits the observations more accurately than L1 although there is still a measurable discordance between the predictions and observations for Europa at the resonance period. [ABSTRACT FROM AUTHOR]

Abstract: The rotation of the main natural satellites of the Solar System is widely assumed to be synchronous, because this corresponds to an equilibrium state. In the case of the Moon, 3 laws have been formulated by Cassini, assuming a spin–orbit resonance and a 1:1 nodal resonance. The recent gravitational data collected by the spacecrafts Galileo (in the jovian system) and Cassini (in the saturnian system) allows us to study the rotation of other natural satellites, and to check the universality of Cassini''s laws. This paper deals with the rotation of the Galilean satellites of Jupiter J-4 Callisto. In this study we use both analytical (like Lie transforms) and numerical methods (numerical detection of chaos, numerical integration, frequency analysis) to first check the reliability of Cassini Laws for Callisto, and then to give a first theory of its rotation, Callisto''s being considered as a rigid body. We first show that the Third Cassini Law (i.e. the nodal resonance), is not satisfied in every reference frame, in particular in the most natural one (i.e. the J2000 jovian equator). The difference of the nodes presents a chaotic-like behavior, that we prove to be just a geometrical illusion. Moreover, we give a mathematical condition ruling the choice of an inertial reference frame in which the Third Cassini Law is fulfilled. Secondly, we give a theory of Callisto''s rotation in the International Celestial Reference Frame (ICRF). We highlight a small motion (i.e. <200 m) of its rotation axis about its body figure, a 11.86-yr periodicity in Callisto''s length-of-day, and the proximity of a resonance that forces 182-yr librations in Callisto''s obliquity. [Copyright &y& Elsevier]

Abstract: Many planetary bodies undergo forced longitudinal librations [Williams, J.G., Boggs, D.H., Yoder, C.F., Ratcliff, J.T., Dickey, J.O., 2001. Lunar rotational dissipation in solid body and molten core. Journal of Geophysical Research-Planets 106 (E11), 27933–27968; Comstock, R.L., Bills, B.G., 2003. A solar system survey of forced librations in longitude. Journal of Geophysical Research-Planets 108 (E9); Margot, J.L., Peale, S.J., Jurgens, R.F., Slade, M.A., Holin, I.V., 2007. Large longitude libration of mercury reveals a molten core. Science 316 (5825), 710–714]. Yet few studies to date have investigated how longitudinal libration, the oscillatory motion of a planet around its rotation axis, couples with its interior planetary fluid dynamics [e.g., Aldridge, K.D., Toomre, A., 1969. Axisymmetric inertial oscillations of a fluid in a rotating spherical container. Journal of Fluid Mechanics 37, 307; Tilgner, A., 1999. Driven inertial oscillations in spherical shells. Physical Review E 59 (2), 1789–1794]. In this study, we investigate, via laboratory experiments, the viscously driven flow in a spherical librating fluid cavity. We focus on libration frequencies less than or equal to the planetary rotation frequency (frequency ratios ), moderate rotation rates (Ekman numbers to ) and a relatively broad range of librational amplitudes (libration amplitudes ; Rossby numbers ). In addition we model flow in three different core geometries: full sphere, and . Direct flow visualizations in the laboratory experiment allow us to identify three distinct librationally driven flow regimes. The transitions between these regimes are governed by critical values of the outer boundary layer Reynolds number, Re. For the flow is dominated by inertial modes. For the system becomes unstable to longitudinal rolls that form beneath the outer boundary. This laminar instability initiates near the equator and is qualitatively similar to Taylor-Görtler instabilities. For the flow in the vicinity of the outer boundary becomes turbulent. For several librating planets with an internal fluid layer, estimates of Re and lie in the range of values accessible in our laboratory experiment. Our results suggest that Mercury, Io, Europa and Titan may undergo boundary layer turbulence, whereas Earth’s moon, Callisto and Ganymede may become unstable to laminar longitudinal rolls. [Copyright &y& Elsevier]

Abstract: An icy satellite whose interior is composed of a homogeneous ice/rock mixture must avoid melting during its entire history, including during its formation when it was heated by deposition of accretional energy and short-lived radioisotopes. Estimates of the temperature rise associated with radiogenic and accretional heating, coupled with limits on satellite melting can be used to constrain the timing of formation of a partially differentiated satellite relative to the origin of the calcium–aluminum-rich inclusions (CAI''s) as a function of its accretion timescale and the protosatellite disk temperature (). Geological characterization and spacecraft radio tracking data suggest that Callisto, the outermost regular satellite of Jupiter, and Saturn''s mid-sized satellite Rhea, are partially differentiated if their interiors are in hydrostatic equilibrium. Because the specific conditions during the satellites'' formation are uncertain, we determine accretional temperature profiles for a range of values for and accretion time scales with the limiting assumption that impactors deposit all their energy close to the surface, leading to maximally effective radiative cooling. We find that Callisto can remain unmelted during formation if it accreted on a time scale longer than 0.6 Myr. Considering both radiogenic and accretional heating, Callisto must have finished accreting no earlier than ∼4 Myr after formation of CAI''s for . Warmer disks or larger impactors that deposit their energy at depth in the satellite would require longer and/or later formation times. If Rhea accreted slowly (in 105 to 106 years), its growth must have finished no earlier than ∼2 Myr after CAI''s for to avoid early melting. If Rhea formed quickly (⩽103 yr), its formation must have been delayed until at least 2 to 7 Myr after CAI''s and in a disk with in the small impactor limit. If the satellites form in slow-inflow-supplied disks as proposed by Canup and Ward [Canup, R.M., Ward, W.R., 2002. Astron. J. 124, 3404–3423], the implied satellite ages suggest that gas inflow to the giant planets ceased no earlier than ∼4 Myr after CAI''s, comparable to average nebular lifetimes inferred from observations of circumstellar disks. [Copyright &y& Elsevier]

Abstract: This paper aims at studying the long-term orbital consequences of the perturbations related to De Haerdtl inequality, a current quasi-commensurability between the Galilean satellites of Jupiter Ganymede and Callisto. We used the method of Frequency Map Analysis to detect a chaotic behavior in a 5-bodies system where every inequality has been dropped, except of De Haerdtl one. We also used Frequency Analysis to draw the behavior of the arguments likely to become resonant, in several numerical integrations. We show that De Haerdtl inequality might have induced chaos in the past if Ganymede''s and Callisto''s eccentricities have been higher than . Moreover, we enlight the influence of Jupiter''s obliquity on this chaos. We also enlight some aspects of this chaotic behavior, showing for instance stable chaos and single resonances. The main result of this study is that De Haerdtl inequality should be taken into account in every study of the long term orbital evolution of the Galilean satellites. [Copyright &y& Elsevier]

Abstract: It has been argued that the dominant non-Newtonian creep mechanisms of water ice make the ice shell above Callisto''s ocean, and by inference all radiogenically heated ice I shells in the outer Solar System, stable against solid-state convective overturn. Conductive heat transport and internal melting (oceans) are therefore predicted to be, or have been, widespread among midsize and larger icy satellites and Kuiper Belt objects. Alternatively, at low stresses (where non-Newtonian viscosities can be arbitrarily large), convective instabilities may arise in the diffusional creep regime for arbitrarily small temperature perturbations. For Callisto, ice viscosities are low enough that convection is expected over most of geologic time above the internal liquid layer for plausible ice grain sizes (⩽a few mm); the alternative for early Callisto, a conducting shell over a very deep ocean (>450 km), is not compatible with Callisto''s present partially differentiated state. Moreover, if convection is occurring today, the stagnant lid would be quite thick (∼100 km) and compatible with the lack of active geology. Nevertheless, Callisto''s steady-state heat flow may have fallen below the convective minimum for its ice I shell late in Solar System history. In this case convection ends, the ice shell melts back at its base, and the internal ocean widens considerably. The presence of such an ocean, of order 200 km thick, is compatible with Callisto''s moment-of-inertia, but its formation would have caused an ∼0.25% radial expansion. The tectonic effects of such a late, slow expansion are not observed, so convection likely persists in Callisto, possibly subcritically. Ganymede, due to its greater size, rock fraction and full differentiation, has a substantially higher heat flow than Callisto and has not reached this tectonic end state. Titan, if differentiated, and Triton should be more similar to Ganymede in this regard. Pluto, like Callisto, may be near the tipping point for convective shutdown, but uncertainties in its size and rock fraction prevent a more definitive assessment. [Copyright &y& Elsevier]

Abstract: Several approaches have been used to estimate the ice shell thickness on Callisto, Ganymede, and Europa. Here we develop a method for placing a strict lower bound on the thickness of the strong part of the shell (lithosphere) using measurements of topography. The minimal assumptions are that the strength of faults in the brittle lithosphere is controlled by lithostatic pressure according to Byerlee''s law and the shell has relatively uniform density and thickness. Under these conditions, the topography of the ice provides a direct measure of the bending moment in the lithosphere. This topographic bending moment must be less than the saturation bending moment of the yield strength envelope derived from Byerlee''s law. The model predicts that the topographic amplitude spectrum decreases as the square of the topographic wavelength. This explains why Europa is rugged at shorter wavelengths (∼10 km) but extremely smooth, and perhaps conforming to an equipotential surface, at longer wavelengths (>100 km). Previously compiled data on impact crater depth and diameter [Schenk, P.M., 2002. Nature 417, 419–421] on Europa show good agreement with the spectral decrease predicted by the model and require a lithosphere thicker than 2.5 km. A more realistic model, including a ductile lower lithosphere, requires a thickness greater than 3.5 km. Future measurements of topography in the 10–100 km wavelength band will provide tight constraints on lithospheric strength. [Copyright &y& Elsevier]

Abstract: We present results of polarimetric observations of the Galilean satellites Io, Europa, Ganymede, and Callisto at phase angles ranging from 0.19° to 2.22°. The observations in the UBVR filters were performed using a one-channel photoelectric polarimeter attached to 70-cm telescope of the Chuguev Observation Station (Ukraine) on November 19–December 7, 2000. We have observed the polarization opposition effect for Io, Europa, and Ganymede to be a sharp secondary spike of negative polarization with an amplitude of about −0.4% centered at phase angles of 0.2°–0.7° and superimposed on the regular negative polarization branch. Although these minima for Io, Europa, and Ganymede show many similarities, they also exhibit a number of distinctions. The polarization opposition effect appears to be wavelength-dependent, at least for Europa and Ganymede. No polarization opposition effect was found for Callisto. The results obtained are discussed within the framework of different mechanisms of light scattering. [Copyright &y& Elsevier]

Abstract: The three icy Galilean moons of Jupiter: Callisto, Ganymede, and Europa, offer a range of exciting science opportunities for space physics and aeronomy. They all have thin atmospheres with residence times of a few days at most. The surface interactions with the space environment determine the atmospheric and ionospheric properties. The Jupiter Icy Moons Orbiter (JIMO) gives possibilities to investigate the weathering properties of their surfaces and volatile material expelled from their interiors. The atmospheres and the ionized ionospheric components of the Galilean moons (including the volcanic moon Io) interact strongly with the co-rotating magnetosphere of Jupiter. This interaction is dynamic and for example triggers energy transfer processes that give rise to auroral signatures at Jupiter. The icy moon’s ionospheres are likewise highly variable in time and estimated peak electron densities vary between 1000 and 20,000cm−3 near their surfaces. A particularly interesting interaction occurs between the magnetosphere of Jupiter and the mini-magnetosphere of Ganymede and its ionosphere. A double-Langmuir probe (LP) experiment orbiting the moons at a short distance for several months will give valuable insight into these processes. Foremost the LP measures in situ plasma density and temperatures of the ionospheric components of the moons with high time resolution and thereby provides estimates of key parameters for the dynamical behaviour of surface weathering and magnetospheric influences. In addition many other physical parameters important to the dynamics of these systems can be estimated with such an instrument, like the plasma flow and the DC electric field. Recent results from the LP part of the Radio and Plasma Wave Science (RPWS) on board the Cassini/Huygens spacecraft orbiting Saturn show that an LP works in extended plasma parameter domains with very good science return. [Copyright &y& Elsevier]

Abstract: Remote observations with the Chandra X-ray Observatory and the XMM-Newton Observatory have shown that the jovian system is a source of X-rays with a rich and complicated structure. The planet''s polar auroral zones and its disk are both powerful sources of X-ray emission. Chandra observations revealed X-ray emission from the Io plasma torus and from the Galilean moons Io, Europa, and possibly Ganymede. The emission from the moons is due to bombardment of their surfaces by highly energetic magnetospheric protons, and oxygen and sulfur ions. These ions excite atoms in their surfaces leading to fluorescent X-ray emission lines. These lines are produced against an intense background continuum, including bremsstrahlung radiation from surface interactions of primary magnetospheric and secondary electrons. Although the X-ray emission from the Galilean moons is faint when observed from Earth orbit, an imaging X-ray spectrometer in orbit around one or more of these moons, operating from 200 eV to 8 keV with 150 eV energy resolution, would provide a detailed mapping of the elemental composition in their surfaces. Surface resolution of 40 m for small features could be achieved in a 100-km orbit around one moon while also remotely imaging surfaces of other moons and Jupiter''s upper atmosphere at maximum regional resolutions of hundreds of kilometers. Due to its relatively more benign magnetospheric radiation environment, its intrinsic interest as the largest moon in the Solar System, and its mini-magnetosphere, Ganymede would be the ideal orbital location for long-term observational studies of the jovian system. Here we describe the physical processes leading to X-ray emission from the surfaces of Jupiter''s moons and the properties required for the technique of imaging X-ray spectroscopy to map the elemental composition of their surfaces, as well as studies of the X-ray emission from the planet''s aurora and disk and from the Io plasma torus. [Copyright &y& Elsevier]

Abstract: We investigate the proposition that Europa and Callisto emit plasma plumes, i.e., a contiguous body of ionospheric plasma, extended in the direction of the corotation flow, analogous to the plume of smoke emitted in the downwind direction from a smokestack. Such plumes were seen by Voyager 1 to be emitted by Titan. We find support for this proposition in published data from Galileo Plasma Science and Plasma Wave observations taken in the corotation wakes of both moons and from magnetometer measurements reported from near the orbit of, but away from, Europa itself. This lends credence to the hypothesis that the plumes escaping from the ionospheres of Europa and Callisto are wrapped around Jupiter by corotation, survive against dispersion for a fairly long time and are convected radially by magnetospheric motions. We present simple models of plume acceleration and compare the plumes of the Europa and Callisto to the known plumes of Titan. [Copyright &y& Elsevier]

Abstract: Recent measurements of the high-energy, omni-directional electron environment by the Galileo spacecraft Energetic Particle Detector (EPD) have been analyzed in the range from 7 to 28 Jupiter radii. 10-min averages of these data between Jupiter orbit insertion in 1995 to the end of the mission have been analyzed to provide estimates of the electron differential fluxes at 1.5, 2, and 11 MeV in the jovian equatorial plane as a function of radial distance. These data provide a long term picture of the variations in the high-energy electron environment over the ∼8 years of the Galileo mission. This paper reviews those measurements and the statistics associated with them for the 8 year period. In general, the data variations are well behaved with variations being within a factor of ∼2 of a median value at a given distance from Jupiter. These results are analyzed in detail and the orbit variations discussed in the context of the overall data set. The results of this analysis of the long-term statistical variations in high-energy electron fluxes are directly applicable to models that estimate the effects of the radiation environment on Jupiter''s moons and their atmospheres as they permit estimates of the possible range of radiation effects that might be expected. [Copyright &y& Elsevier]

Abstract: Models of the internal structure of completely differentiated Europa and partially differentiated Callisto have been constructed on the basis of Galileo gravity measurements, geochemical constraints on composition of ordinary and carbonaceous chondrites, and thermodynamic data on the equations of state of water, high-pressure ices, and meteoritic material. We assume thermal and mechanical equilibrium for the interiors of the satellites. A geophysically and geochemically permissible thickness of Europa''s outer water–ice shell lies between 105 and 160 km (6.2–9.2% of total mass). Our results show that the bulk composition of the rock–iron core of Europa may be described by material approaching the L/LL-type chondrites in composition, but cannot be correlated either with the material of CI chondrites or H chondrites. For Europa''s L/LL-chondritic models, core radii are estimated to be 470–640 km (5.3–12.5% of total mass). The allowed thickness of Europa''s H2O layer ranges from for a differentiated L/LL-type chondritic mantle with a crust to for an undifferentiated mantle. We show that Callisto must only be partially differentiated into an outer ice-I layer, a water ocean, a rock–ice mantle, and a rock–iron core (mixture of anhydrous silicates and/or hydrous silicates + Fe). We accept that the composition of the rock–iron material of Callisto is similar to the bulk composition of L/LL-type chondritic material containing up to 10–15% of iron and iron sulfide. Assuming conductive heat transfer through the ice-I crust [Ruiz, 2001. The stability against freezing of an internal liquid-water ocean on Gallisto. Nature, 412, 409–411], heat flows were estimated and the possibility of the existence of a water ocean in Callisto was evaluated. The liquid phase is stable (not freezing) beneath the ice crust, if the heat flow is between 3.3 and 3.7 mW m−2, which corresponds to the heat flow from radiogenic sources. The thickness of the ice-I crust is 135–150 km, and that of the underlying water layer, 120–180 km. The results of modeling support the hypothesis that Callisto may have an internal liquid-water ocean. The allowed total (maximum) thickness of the outer water–ice shell is up to 270–315 km. Rock–iron core radii, depending on the presence or absence of hydrous silicates, do not exceed 500–700 km, the thickness of an intermediate ice–rock mantle is not less than 1400 km, and its density is in the range of 1960–2500 kg m−3. The surface temperature of Callisto is expected to be 100–112 K. The total amount of H2O in Callisto is found to be 49–55 wt%. The correspondence between the density and moment of inertia values for bulk ice-free Io, rock–iron core of ice-poor Europa, and rock–iron cores of Ganymede and Callisto shows that their bulk compositions may be, in general, similar and may be described by the composition close to a material of the L/LL-type chondrites with the (Fetot/Si) weight ratios ranging from 0.9 to 1.3. Planetesimals composed of these types of ordinary chondrites could be considered as analogues of building material for the rock–iron cores of the Galilean satellites. Similarity of bulk composition of the rock–iron cores of the inner and outer satellites implies the absence of iron–silicon fractionation in the protojovian nebula. [Copyright &y& Elsevier]