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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]

The icy Galilean satellites display impact crater morphologies that are rare in the Solar System. They deviate from the archetypal sequence of crater morphologies as a function of size found on rocky bodies and other icy satellites: they exhibit central pits in place of peaks, followed by central dome craters, anomalous dome craters, penepalimpsests, palimpsests, and multi‐ring structures. Understanding the origin of these features will provide insight into the geophysical factors that operate within the icy Galilean satellites. Pit craters above a size threshold feature domes. This trend, and the similarity in morphology between the two classes, suggest a genetic link between pit and dome craters. We propose that dome craters evolve from pit craters through topographic relaxation, facilitated by remnant heat from the impact. Our finite element simulations show that, for the specific crater sizes where we see domes on Ganymede and Callisto, domes form from pit craters within 10 Myr. Topographic relaxation eliminates the stresses induced by crater topography and restores a flat surface: ice flows downwards from the rim and upwards from the crater depression driven by gravity. When the starting topography is a pit crater, the heat left over from the impact is concentrated below the pit. Since warm ice flows more rapidly, the upward flow is enhanced beneath the pit, leading to the emergence of a dome. Given the timescales and the dependence on heat flux, this model could be used to constrain the thermal history and evolution of these moons. Plain Language Summary: Ganymede and Callisto are large icy moons orbiting Jupiter, believed to be ocean worlds. These moons' surfaces display impact craters with shapes not seen elsewhere in the Solar System. This may be due to factors such as their high gravity, temperature, presence of subsurface oceans, and/or impactor characteristics. By exploring these atypical craters, we aim to shed light on the inner workings and evolution of these moons and, by extension, contribute to a clearer picture of the evolution of the outer Solar System. This study focuses on unveiling the origins of dome craters on Ganymede and Callisto, which have rounded bright domes in the center and are virtually unique to these moons. We believe these domes are connected to a relatively more common crater, the pit crater. Our simulations show that a pit crater can evolve into a dome crater within 10 million years as the ice flows slowly under its own weight. This flow is channeled back into the center creating a dome, aided by warm temperatures left over from the impact that soften the ice below the pit. This occurs only for the specific sizes where we see dome craters on these moons. Key Points: Dome craters form via topographic relaxation of pit craters for sizes larger than ∼60 kmRemnant heat from the impact enhances relaxation at the center of the pit crater, causing domes to emergeEven young dome craters can form from the relaxation of pit craters due to the relatively short timescales required (∼10 million years) [ABSTRACT FROM AUTHOR]

The ionospheres of Jupiter's icy moons have been observed by in situ plasma measurements and radio science. However, their spatial structures have not yet been fully characterized. To address this, we developed a new ray tracing method for modeling the radio occultation of the ionospheres using Jovian auroral radio sources. Applying our method to Jovian auroral radio observations with the Galileo spacecraft, we derived the electron density of the ionosphere of Ganymede and Callisto. For Ganymede's ionosphere, we found that the maximum electron density on the surface was 76.5–288.5 cm−3 in the open magnetic field line regions and 5.0–20.5 cm−3 in the closed magnetic field line region during the Galileo Ganymede 01 flyby. The difference in the electron density distribution was correlated with the accessibility of Jovian magnetospheric plasma to the atmosphere and surface of the moons. These results indicated that electron‐impact ionization of the Ganymede exosphere and sputtering of the surface water ice were effective for the producing Ganymede's ionosphere. For Callisto's ionosphere, we found that the densities were approximately 350 and 12.5 cm−3 on the night side hemisphere during Callisto 09 and 30 flybys, respectively. These results combined with previous observations indicated that atmospheric production through sublimation controlled the ionospheric density of Callisto. This method is also applicable to upcoming Jovian radio observation data from the Jupiter Icy Moon Explorer, JUICE. Key Points: We developed a ray tracing method for Jupiter's icy moon ionospheric occultation of Jovian auroral radio sourcesThe ionospheric density of Ganymede is associated with electron‐impact ionization and atmospheric production via ion sputteringThe Ionospheric density of Callisto is associated with atmospheric production by solar illumination on its surface [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]

This study focuses on constraining the role that Callisto's perturbed electromagnetic environment had on energetic charged particle signatures observed during the Galileo mission. To do so, we compare data from the Energetic Particle Detector (EPD) obtained during four close encounters of the moon with a model framework that combines hybrid simulations for low‐energy plasma and test‐particle tracing simulations for high‐energy particles. By comparing model results for energetic particle dynamics in both uniform and perturbed electromagnetic fields, we systematically disentangle the role that geometric effects (i.e., absorption of particles by Callisto's solid surface) have on observed energetic particle signatures compared to those associated with Callisto's perturbed electromagnetic environment (generated by the moon's induced magnetic field and plasma interaction currents). We show that observed flux drop‐outs in the energetic ion pitch angle distributions (PADs) are largely driven by their absorption by Callisto's surface: their large gyroradii exceed the size of the moon, facilitating their impact onto the icy surface and preventing their detection by EPD. However, features observed in the energetic electron PADs can only be explained with an accurate representation of the moon's perturbed environment, since electrons closely follow the orientation of the electromagnetic fields. Our findings therefore illustrate the key role that the moon's induced field and magnetospheric plasma interaction have on the dynamics of energetic electrons, emphasizing the importance of accurately modeling Callisto's locally perturbed electromagnetic environment when attempting to interpret data from past and future encounters, including those anticipated from the upcoming JUICE mission. Plain Language Summary: Jupiter's moon Callisto is continuously exposed to a combination of low‐energy plasma and high‐energy charged particles. As the moon interacts with these populations, its local electromagnetic field environment becomes highly perturbed. During four Callisto encounters during the Galileo mission to Jupiter, a sensor onboard the spacecraft detected clear signatures of the high‐energy ions and electrons. To understand the degree to which Callisto's low‐energy plasma interaction affects these signatures, we systematically model the dynamics of energetic particles as they travel through various electromagnetic field configurations. We find that the energetic ion observations are not strongly affected by the perturbed fields, but instead can be understood in terms of the particles being absorbed by Callisto's solid surface. However, electrons are highly sensitive to the draped fields, and the Galileo observations can only be understood when considering the perturbed electromagnetic environment near the moon. Our results underscore the importance of accurately modeling Callisto's perturbed environment when hoping to understand energetic particle signatures observed during the upcoming JUICE mission. Key Points: We compare energetic charged particle data with a model to explain pitch angle distributions observed during four Galileo flybys of CallistoElectron flux drop‐outs are shaped by the perturbed fields associated with Callisto's induced field and magnetospheric plasma interactionObserved ion fluxes can be mainly explained through geometric considerations, with Callisto's surface shadowing particles from detection [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]

Small planetary bodies in the solar system, including Io, Ganymede, and Callisto, may have a crust denser than their underlying mantle. Despite the inherent gravitational instability of such structures, we show that the growth timescale of the Rayleigh–Taylor (RT) instability can be as long as the age of the solar system, owing to the strong temperature dependence of viscosity. Even in cases where the instability timescale is shorter, the instability is confined to a thin layer at the base of the crust, making the foundering of the entire crust improbable in many scenarios. This study delineates the onset and aftermath of the RT instability, applying a quantitative framework to assess the stability of (i) rock-contaminated crust on icy satellites, and (ii) silicate crust floating on top of a subsurface magma ocean on Io. Notably, for Io the RT instability peels off only 10–100 m from the crust’s base, and thermal diffusion rapidly recovers the crustal thickness through solidification of a magma ocean. Despite recurrent delamination of the crustal base, the initial crustal thickness is maintained by thermal diffusion, virtually stabilizing a floating dense crust. Cracking of the crust also is unlikely to result in the foundering of the crust. A dense crust on a small body is therefore difficult to be overturned, suggesting the potential ubiquity of dense surface layers throughout the solar system.

To better assess the role that electrons play in exosphere production on icy bodies, we measured the total and O _2 sputtering yields from H _2 O ice for electrons with energies between 0.75 and 10 keV and temperatures between 15 and 124.5 K. We find that both total and O _2 yields increase with decreasing energy over our studied range, that they increase rapidly at temperatures above 60 K, and that the relative amount of H _2 O in the sputtered flux decreases quickly with increasing energy. Combining our data with other electron data in the literature, we show that the accuracy of a widely used sputtering model can be improved significantly for electrons by adjusting some of the intrinsic parameter values. Applying our results to Europa, we estimate that the contribution of electrons to the production of the O _2 exosphere is equal to the combined contribution of all ions. In contrast, sputtering of O _2 from Ganymede and Callisto appears to be dominated by irradiating ions, though electrons still likely contribute a nonnegligible amount. While our estimates could be further refined by examining the importance of spatial variations in electron flux, we conclude that, at the very least, electrons seem to be important for exosphere production on icy surfaces and should be included in future modeling efforts.

China will launch the “Tianwen-IV” mission around 2030, focusing on the orbiting exploration of Jupiter and Callisto, a moon of Jupiter. As part of this ambitious mission, a main satellite will carry another satellite that will be released in the Jupiter system to continue its journey toward Uranus. Considering the current mission planning, we propose an inter-satellite radio-observation mode that differs from the conventional observation mode of tracking from Earth to precisely determine the orbit of the satellites. Given the significance of the Callisto gravity field model in both science objectives and satellite navigation, we have conducted a series of simulation experiments to evaluate the potential of this inter-satellite range-rate data for accurately estimating the Callisto gravity field. The results obtained from the analysis demonstrate that by utilizing 40 days of ground station observations, it is possible to estimate the gravity field model of Callisto up to a degree of 70. Remarkably, when combining these ground station observations with inter-satellite observations, a comparable level of accuracy can be achieved with just 10 days of observations. Furthermore, with reduced inter-satellite observation noise, accuracy improves, enabling estimation up to 80 degrees or higher. Initial inter-satellite distance selection impacts estimation accuracy. These findings serve as a valuable test bed for the future “Tianwen-IV” mission to perform precise orbit determination and gravity field model estimation to reduce reliance on deep space stations.

We analyzed spectral cubes of Callisto’s leading and trailing hemispheres, collected with the NIRSpec Integrated Field Unit (G395H) on the James Webb Space Telescope. These spatially resolved data show strong 4.25 μ m absorption bands resulting from solid-state ^12 CO _2 , with the strongest spectral features at low latitudes near the center of its trailing hemisphere, consistent with radiolytic production spurred by magnetospheric plasma interacting with native H _2 O mixed with carbonaceous compounds. We detected CO _2 rovibrational emission lines between 4.2 and 4.3 μ m over both hemispheres, confirming the global presence of CO _2 gas in Callisto’s tenuous atmosphere. These results represent the first detection of CO _2 gas over Callisto’s trailing side. The distribution of CO _2 gas is offset from the subsolar region on either hemisphere, suggesting that sputtering, radiolysis, and geologic processes help sustain Callisto’s atmosphere. We detected a 4.38 μ m absorption band that likely results from solid-state ^13 CO _2 . A prominent 4.57 μ m absorption band that might result from CN-bearing organics is present and significantly stronger on Callisto’s leading hemisphere, unlike ^12 CO _2 , suggesting these two spectral features are spatially antiassociated. The distribution of the 4.57 μ m band is more consistent with a native origin and/or accumulation of dust from Jupiter’s irregular satellites. Other, more subtle absorption features could result from CH-bearing organics, CO, carbonyl sulfide, and Na-bearing minerals. These results highlight the need for preparatory laboratory work and improved surface–atmosphere interaction models to better understand carbon chemistry on the icy Galilean moons before the arrival of NASA’s Europa Clipper and ESA’s JUICE spacecraft.

Prior to landing of reusable space transportation systems, the vehicle's landing legs needs to be fully deployed to enable a safe landing and further re-use of the space vehicle. During that phase the deployment system has to overcome harsh and challenging environmental conditions. In this study, a numerical simulator is developed in order to investigate these influences on the landing leg deployment dynamics. By means of an extensive aerodynamic database and a broad approach flight domain, the influence of aerodynamics, exhaust plume, and vehicle's attitude on the deployment dynamics is analyzed. This study shows on the example of the first stage demonstrator CALLISTO (Cooperative Action Leading to Launcher Innovation in Stage Toss back Operations), that thrust level, vehicle attitude, and the deployment system parameters affect the deployment performance. [ABSTRACT FROM AUTHOR]

This study investigates how Callisto's perturbed electromagnetic environment—generated by the moon's interaction with the low‐energy Jovian magnetospheric plasma—affects the dynamics of high‐energy ions and electrons. We constrain how these perturbed fields influence the energetic particle fluxes deposited onto the top of Callisto's atmosphere between energies of 4.5 keV ≤ E ≤ 11.8 MeV. We use a hybrid simulation to model the variability in Callisto's perturbed electromagnetic environment over a synodic period by considering three representative scenarios of the moon's plasma interaction, corresponding to various distances of the moon to the Jovian magnetospheric current sheet. The local field perturbations are maximized near the center of the sheet (forming, e.g., signatures of field‐line pileup, draping, and Alfvén wings) whereas far from the sheet, a mere superposition of the moon's induced dipole with the background field largely explains the perturbations. We then apply a test‐particle approach to investigate the dynamics of energetic electrons and ions (protons, oxygen, and sulfur) while exposed to these fields. Since electron gyroradii are smaller than Callisto, the field perturbations generate small‐scale non‐uniformities in their flux patterns onto the moon, while the ion flux patterns are more homogeneous. Energetic electrons dominate the number flux onto the atmosphere, whereas ions dominate the energy flux. Over a synodic period, the flux patterns onto Callisto's exobase closely resemble those when the moon is near the current sheet center, since the differential energetic particle fluxes in the ambient plasma decrease by an order of magnitude when the moon travels far outside of the sheet. Plain Language Summary: Callisto's ambient plasma environment is comprised of low‐ and high‐energy particles from Jupiter's magnetosphere that continually bombard the moon. Callisto's interaction with the low‐energy population generates currents that locally perturb the electric and magnetic fields, the structures of which vary periodically over a full rotation of Jupiter. These perturbed electromagnetic fields, in turn, strongly affect the dynamics of the high‐energy population—particles that are responsible for partially ionizing Callisto's atmosphere and sputtering the icy surface. This study constrains the degree to which these energetic ions and electrons are affected by Callisto's perturbed electromagnetic environment. We investigate how the high‐energy irradiation of Callisto's atmosphere varies not only with latitude and longitude, but also throughout the moon's orbit around its parent planet. We show that the electron influx patterns strongly depend on Callisto's location within the Jovian magnetosphere, while the ion patterns are more robust against changes to the moon's local environment. Key Points: We calculate the effect of Callisto's perturbed electromagnetic environment on energetic particle fluxes onto the top of the atmosphereElectron flux patterns are strongly affected by Callisto's plasma interaction, while ion fluxes are nearly uniform in the perturbed fieldsFluxes onto the exobase are largest within the Jovian current sheet, despite strong field perturbations generated by the plasma interaction [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]

We present a thermal observation of Callisto's leading hemisphere obtained using the Atacama Large Millimeter/submillimeter Array at 0.87 mm (343 GHz). The angular resolution achieved for this observation was ∼0.″16, which for Callisto at the time of this observation ( D ∼ 1.″05) was equivalent to ∼six elements across the surface. Our disk-integrated brightness temperature of 116 ± 5 K (8.03 ± 0.40 Jy) is consistent with prior disk-integrated observations. Global surface properties were derived from the observation using a thermophysical model constrained by spacecraft data. We find that models parameterized by two thermal inertia components more accurately fit the data than single thermal inertia models. Our best-fit global parameters adopt a lower thermal inertia of 15–50 J m ^−2 K ^−1 s ^−1/2 and a higher thermal inertia component of 1200–2000 J m ^−2 K ^−1 s ^−1/2 , with retrieved millimeter emissivities of 0.89–0.91. We identify several thermally anomalous regions, including spots ∼3 K colder than model predictions colocated with the Valhalla impact basin and a complex of craters in the southern hemisphere; this indicates the presence of materials possessing either a higher thermal inertia or a lower emissivity. A warm region confined to the midlatitudes in these leading hemisphere data may be indicative of regolith property changes due to exogenic sculpting.

The tenuous atmospheres of the Galilean satellites are sourced from their surfaces and produced by a combination of plasma-surface interactions and thermal processes. Even though they are thin, these atmospheres can be studied via their auroral emissions, and most work to date has focused on their aurorae at UV wavelengths. Here we present the first detections of the optical aurorae of Ganymede and Callisto, as well as detections of new optical auroral lines at Europa, based on observations of the targets over 10 Jupiter eclipses from 1998 to 2021 with Keck/HIRES. We present measurements of O i emission at 6300/6364, 5577, 7774, and 8446 Å and place upper limits on hydrogen at 6563 Å. These constitute the first detections of emissions at 7774 and 8446 Å at a planetary body other than Earth. The simultaneous measurement of multiple emission lines provides robust constraints on atmospheric composition. We find that the eclipse atmospheres of Europa and Ganymede are composed predominantly of O _2 , with average column densities of (4.1 ± 0.1) × 10 ^14 cm ^−2 and (4.7 ± 0.1) × 10 ^14 cm ^−2 , respectively. We find weak evidence for H _2 O in Europa's bulk atmosphere at an H _2 O/O _2 ratio of ∼0.25, and place only an upper limit on H _2 O in Ganymede's bulk atmosphere, corresponding to H _2 O/O _2 < 0.6. The column density of O _2 derived for Callisto is (4.0 ± 0.9) × 10 ^15 cm ^−2 for an assumed electron density of 0.15 cm ^−3 , but electron properties at Callisto's orbit are very poorly constrained.

The Earth is influenced by the effects of the continuously varying solar wind, the flow of plasma and the embedded magnetic field from the Sun. Life on the earth is driven by the sunlight incident from the Sun. Therefore, the climate is critically sensitive to solar activities. The variation in the Sun's atmosphere has an important role in changing life on the earth and therefore it becomes necessary to monitor, observe and study solar activities. Many instruments and observatories have been keeping watch on Sun's activities. The Compound Astronomical Low-cost Low-frequency Instrument for Spectroscopy and Transportable Observatory (CALLISTO) is one of them. It is popular, portable and low-cost instrument. All CALLISTO station spectrometers together form an e-CALLISTO network. The e-CALLISTO network is spread worldwide and has been providing observations from different countries. This paper reports the antenna and receiver of e-CALLISTO network. It represents the information about antenna especially Log-periodic Dipole Antenna (LPDA) which is low cost and easy to design which can help antenna designer to identify the benefits of LPDA. The e-CALLISTO network is still growing, therefore this may help the people who are going to work on solar activity or working on the e-CALLISTO network. [ABSTRACT FROM AUTHOR]

JAXA, CNES and DLR have decided to join their force to develop and fly a scaled reusable VTVL rocket stage called CALLISTO (Cooperative Action Leading to Launcher Innovation in Stage Toss - back Operations). This vehicle will pave the way for future reusable launch vehicles. One of its main goals is to demonstrate the mastering of key techniques and technologies that will be needed later by operational reusable launch vehicles. Indeed in the frame of CALLISTO numerous challenging technologies are being matured for the specific case of reusable launch vehicles. The challenges of a selection of key technologies developed for CALLISTO are discussed and the solutions retained for CALLISTO are presented. [ABSTRACT FROM AUTHOR]

Upstream the invention of female homosexuality, research focuses on the visibility of a lesbian éros in modern art, around the figure of the couple, in the representations of Ovid's Metamorphoses linked to the stories of Diana and Actaeon and of Diana and Callisto. The critical gaze is less on the metamorphosis itself as mutation of genders, than on edge figures, which bring into play in the visual device couples of nymphs around Diana at the bath. Lesbian erotica associated with gesture of intimacy questions the affects at the origin of the works, a certain desire to see conveyed by the patriarchal imagination, as it questions the place of the contemporary viewer: how to gaze according to its gender and sexuality?

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]

Investigations related to the impact caused by solar radio burst emissions on space weather forecasting and human activities have been ongoing for a long time. Solar activities based on radio spectra are recorded by using a radio spectrometer from ground Earth. Currently, manual observations are conducted for burst detection using the Compound Astronomical Low-Cost Low-Frequency Instrument for Spectroscopy and Transportable Observatory (CALLISTO) spectrometer that is able to generate more than one thousand spectra a day at each station. This Burst-Finder was developed to automatically detect the presence of solar radio bursts from the spectra using MATLAB. This study processed 1491 CALLISTO spectra images from 31 stations on 11 February 2014, in which Type II and Type III burst occurrences were detected. The success rate for burst detection was about 89%. This automated system offers CALLISTO uses an effortless and hassle-free tool for burst detection in order to monitor solar bursts during a complete cycle of 11 years. [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]

Purpose: To compare a new no-touch alignment technique for toric intraocular lenses (IOL) with the conventional technique that uses a manual pendulum. Methods: In this retrospective case–control study, patients who underwent toric IOL implantation using two different alignment techniques (digital Callisto® system vs. manual-pendulum-based marking) were compared in a vector analysis using the Alpins method and an analysis of variance regarding corrected and uncorrected visual acuity and the deviation of the achieved IOL axis from the targeted axis. Results: Sixty-one eyes were included into analysis. Thirty-six of these surgeries were performed via the Callisto® system and 25 eyes via pendulum-based corneal markings. Median IOL axis misalignment was 3° in both groups. Median uncorrected distance visual acuity was 0.097 logMAR versus 0.200. Median best-corrected visual acuity was 0.000 logMAR versus 0.097. All these data were below the range of statistical significance (p > 0.05). Vector analysis showed no significant difference for TIA [median of 3.14 diopters (D) vs. 2.73 D], SIA (median of 3.82 D vs. 3.79 D), DV (1.18 D vs. 1.08 D), and CI (1.23 vs. 1.29). Median angle of error was 1.96° versus − 0.44° (p > 0.05). Conclusions: We found no significant difference in the refractive results, the IOL positioning, and the best-corrected and uncorrected distance visual acuity between the two compared methods. Nevertheless, the Callisto® IOL alignment system delivers a standardized and easy-to-use technology. In particular, less-experienced surgeons might benefit from this marking technique. [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]

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 f* ≤ 1), moderate rotation rates (Ekman numbers E = 1 0- 4 to 1 0- 5) and a relatively broad range of librational amplitudes (libration amplitudes 10 ° ≲ Δ φ{symbol} ≲ 200 °; Rossby numbers 0.03 ≲ R o ≲ 5). In addition we model flow in three different core geometries: full sphere, rinner ≃ 0.6 router and rinner ≃ 0.9 router. 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 R e ≲ 20 the flow is dominated by inertial modes. For 20 ≲ R e ≲ 120 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 R e ≳ 120 the flow in the vicinity of the outer boundary becomes turbulent. For several librating planets with an internal fluid layer, estimates of Re and f* 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.

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]