The JUpiter ICy moons Explorer (JUICE), the first large-class of the European Space Agency (ESA), is planned to launch in 2023, and one of its main goals is to make detailed observations of Jupiter’s moon Ganymede. The mission will investigate the past and/or recent cryovolcanic and tectonic activity of the moon and the exchange processes with the subsurface and possibly with the ocean. Recently, the science team defined “potential cryovolcanic regions” as a category of high interest for observation by JUICE (Stephan et al., 2021). For preparation of the scientific return of the mission, it is important to study in detail the regions that are considered to be good candidates for past/present activity. Light material areas on Ganymede imaged by Voyager have been suggested to represent dark terrain resurfaced by cryovolcanic flows (e.g., Parmentier et al., 1982), while the dark terrain’s speculated cryovolcanic origin was later disputed based on higher-resolution images of the Galileo mission. Additional Galileo data showed the significant role of tectonism in the formation of the light material areas, while the role of cryovolcanism remained inconclusive. Currently, small, isolated depressions called ‘paterae’, are the best candidate regions for cryovolcanic activity on Ganymede and suggested to be potential caldera-like cryovolcanic source vents (e.g., Spaun et al., 2001). Their nature has been interpreted as “possible cryovolcanic source vents for extrusion of clean icy material to form light material units” (Collins et al., 2013), and their small size is consistent with a cryovolcanic origin that operates on a local scale. The high-resolution JUICE camera, JANUS, in combination with other remote sensing instruments, is expected to resolve many of the mysteries concerning cryovolcanism on Ganymede and the origin of the moon’s varied geologic features. The “potential cryovolcanic regions” identified by the JUICE team includes 19 out of 30 paterae mapped by Collins et al., (2013) using Voyager and Galileo images. In this study, with the aim to enhance the preparation of the JUICE mission and its science return, we present: a thorough view of all 19 paterae regions; a detailed geomorphological characterization and comparison between the Ganymede paterae with paterae from other planetary bodies; and a spectral assessment using Galileo NIMS data.

Knowledge of the radiant energy budgets and internal heat of planets and moons is of wide interest in the planetary science community. Some progress has been achieved with recent studies, but there are still significant limitations in current observations and studies. We recommend future exploration to better understand the radiant energy budgets and internal heat of planets and moons in our solar system. 1. Big picture and significance As a fundamental parameter of planets and moons, the radiant energy budget is determined by the absorbed solar energy and the emitted thermal energy (1, 2). Such an energy budget plays an important role in determining the thermal structures of planets and moons (3-6). It can help us understand the geology (e.g., polar ices of Mars) (7), internal heat related to the formation and evolution of giant planets [8-10], and sub-surface internal heat driving the jet plumes on some moons (11-15). For bodies with atmospheres, the radiant energy budgets at the top of atmospheres also set critical boundary conditions for the atmospheric systems (3). The transfer and distribution of radiant energies within the atmospheric systems modify the thermal structure to generate available potential energy. The available potential energy can be converted into kinetic energy to drive atmospheric circulation and the related weather and climate (3-6, 16, 17). Unfortunately, the global radiant energy budget has not been well determined for most of planets and moons (4-6) in our solar system, mainly because the observations of the radiant energies are limited (1, 2, 18, 19). With the advance of space exploration, we expect to get a much better picture of the global radiant energy budget and internal heat for the planets and moons in our solar system. 2. Methodology and observations To determine the radiant energy budgets and hence the internal heat of planets and moons, we have to measure two radiant energies – the absorbed solar energy and the emitted thermal energy. The emitted thermal energy of planets and moons in our solar system is concentrated in the infrared wavelengths, which can be measured by an instrument in the wavelength range 5-400 microns. On the other hand, the solar energy from the Sun is mainly concentrated in the ultraviolet, visible and near-infrared wavelengths (0-5 microns). Generally, we measure the reflected solar energy and then compute the absorbed solar energy. The precise measurements of the emitted thermal energy and the reflected solar energy require accurate observations with complete coverage of wavelength and viewing angles (e.g., emission angle and phase angle). The basic methodology of computing the radiant energies is to integrate the radiance over wavelength and viewing angle, which is described in detail in our previous studies (18, 19). The difference between the emitted thermal energy and the absorbed solar energy is generally used to estimate the internal heat of planets and moons

Uranus and Neptune are the archetypes of "ice giants", a class of planets that may be among the most common in the Galaxy. They hold the keys to understand the atmospheric dynamics and structure of planets with hydrogen atmospheres inside and outside the solar system; however, they are also the last unexplored planets of the Solar System. Their atmospheres are active and storms are believed to be fueled by methane condensation which is both extremely abundant and occurs at low optical depth. This means that mapping temperature and methane abundance as a function of position and depth will inform us on how convection organizes in an atmosphere with no surface and condensates that are heavier than the surrounding air, a general feature of giant planets. Owing to the spatial and temporal variability of these atmospheres, an orbiter is required. A probe would provide a reference atmospheric profile to lift ambiguities inherent to remote observations. It would also measure the abundances of noble gases which can be used to reconstruct the history of planet formation in the Solar System. Finally, mapping the planets' gravity and magnetic fields will be essential to constrain their global composition, atmospheric dynamics, structure and evolution. An exploration of Uranus or Neptune will be essential to understand these planets and will also be key to constrain and analyze data obtained at Jupiter, Saturn, and for numerous exoplanets with hydrogen atmospheres.

We explore the possibility that Callisto’s ocean sits beneath its high-pressure ice, rather than above it. Oceans perched between ice phases are considered to be stable configurations for Ganymede, Callisto, and Titan. High-pressure ices under the liquid water ocean will transport heat and solutes into the ocean as long as the convective adiabat for the ices remains close to the melting temperature (Choblet et al. 2017, Kalousova and Sotin 2018). However, this configuration may become unstable when the perched ocean is close to freezing and its salinity increases, if the ocean becomes denser than the underlying ice. Among the oceans in the solar system, Callisto’s must be among the coldest and most saline because the internal heat appears to be low in the absence of tidal dissipation. Surface geology indicates its lithosphere is fully stagnant (Moore et al. 2004). Solid-state convection may continue beneath less than 100 km or dirty non-convecting ice (McKinnon 2006). And just below this layer may reside a liquid water ocean that is the lag deposit of Callisto’s thicker primordial ocean, the concentrated result of 4 Gyr of freezing. Using representative interior structures based on the current constraints from the Galileo mission (Anderson et al. 2001) coupled with recently obtained thermodynamic data (Vance et al. 2018), we demonstrate the possibility for using magnetic induction to identify where the ocean currently resides in Callisto. Anderson, J. D. et al. (2001). Shape, mean radius, gravity field, and interior structure of Callisto. Icarus, 153(1):157–161. Choblet, G. et al. (2017). Heat transport in the high-pressure ice mantle of large icy moons. Icarus, 285:252–262. Kalousovà, K. and Sotin, C. (2018). Melting in high-pressure ice layers of large ocean worlds - implications for volatiles transport. Geophysical Research Letters. McKinnon, W. (2006). On convection in ice I shells of outer solar system bodies, with detailed application to Callisto. Icarus, 183(2):435–450. Moore, et al. (2004). Callisto. Jupiter. The Planet, Satellites and Magnetosphere, 1:397–426. Moore, J. and Pappalardo, R. (2011). Titan: An exogenic world? Icarus, 212:790–806. Vance, S. D. et al. (2018). Geophysical investigations of habitability in ice-covered ocean worlds. Journal of Geophysical Research: Planets, 123, 180–205.

Earth and Space Science Open Archive PosterOpen AccessYou are viewing the latest version by default [v1]Dependence of Convective Dynamo Action on Bulk Electrical ConductivityAuthorsKristaSoderlundJonathanAurnouSee all authors Krista SoderlundCorresponding Author• Submitting AuthorUniversity of Texas at Austinview email addressThe email was not providedcopy email addressJonathan AurnouUniversity California, Los Angelesview email addressThe email was not providedcopy email address

Future remote sensing of exoplanets will be enhanced by a thorough investigation of our solar system Ice Giants (Neptune-size planets). What can the configuration of the magnetic field tell us (remotely) about the interior, and what implications does that field have for the structure of the magnetosphere; energy input into the atmosphere, and surface geophysics (for example surface weathering of satellites that might harbour sub-surface oceans). How can monitoring of auroral emission help inform future remote observations of emission from exoplanets? Our Solar System provides the only laboratory in which we can perform in-situ experiments to understand exoplanet formation, dynamos, systems and magnetospheres.

The Visual and Infrared Mapping Spectrometer (VIMS) instrument aboard the Cassini spacecraft obtained its first spectral map of the satellite Iapetus in which new absorption bands are seen in the spectra of both the low-albedo hemisphere and the H2O ice-rich hemisphere. Carbon dioxide is identified in the low-albedo material, probably as a photochemically produced molecule that is trapped in H2O ice or in some mineral or complex organic solid. Other absorption bands are unidentified. The spectrum of the low-albedo hemisphere is satisfactorily modeled with a combination of organic tholin, poly-HCN, and small amounts of H2O ice and Fe2O3. The high-albedo hemisphere is modeled with H2O ice slightly darkened with tholin. The detection of CO2 in the low-albedo material on the leading hemisphere supports the contention that it is carbon-bearing material from an external source that has been swept up by the satellite's orbital motion.