The European Space Agency's (ESA) JUICE mission (JUpiter ICy moons Explorer) is en route to the Jovian system to characterize Ganymede's subsurface ocean. Determining the ocean's conductivity and depth requires precise measurements of its induced magnetic field at the position of JUICE. Electron reflectometry provides additional constraints for the surface magnetic field, but this would require knowledge of Ganymede's surface electric potential. Here, we model the global electrostatic surface potential distribution on Ganymede using a semi-analytical charging formulation, by feeding it with surface plasma environment parameters derived from different magnetospheric interaction simulations. We further contrast these estimates against self-consistent charging simulations using the Spacecraft Plasma Interaction Software (SPIS). Our results indicate that surface potentials should be mostly negative, ranging down to about -100 V. All model predictions exhibit a consistent morphological trend: closed field line regions are more negatively charged than open field line ones. Depending on the input used, the driver behind this trend can either be the spatial variations of plasma density alone or combined density and electron temperature patterns, especially in the ionosphere; the electron current is the dominant driver of surface potential, with the relative influence of secondary electron, ion, and photoelectron currents varying depending on the location at Ganymede. While estimates of absolute surface potential are consistent with aspects of Juno flyby data, they are heavily dependent on how simulated plasma parameters are extrapolated to Ganymede's surface. Consequently, advanced modeling is required to achieve more reliable constraints of Ganymede's near-surface environment description.

Radiation belts are regions of magnetically trapped particle radiation found around all of the sufficiently magnetized planets in the Solar System and recently also observed around brown dwarfs, yet despite their ubiquity, there is not yet a general theory or model to predict the uppermost energy limits that any particular magnetospheric system's radiation belts can attain. By considering only the most fundamental loss processes, a model and corresponding theory are developed that successfully bound and explain the maximum observed energies of all documented radiation belt systems. Interestingly, this approach yields a relatively simple function for the uppermost energy limit that depends on only the surface magnetic field strength of the system. The model predicts an energy limit for all radiation belt systems that asymptotes at 7 +/- 2 TeV (for protons and electrons), offering intriguing new insight on potential sources of galactic cosmic rays. This model is also applied to an exoplanetary system, demonstrating that the planet is likely a synchrotron emitter and showcasing the model's use for identifying candidate targets for synchrotron-emitting astrophysical systems and revealing details critical to habitability at those remote worlds.

We review the current state of understanding of Ceres as it relates to planetary protection policy for future landed missions, including for sample return, to the dwarf planet. The Dawn mission found Ceres to be an intriguing target for a mission, with evidence for the presence of regional, possibly extensive liquid at depth, and local expressions of recent and potentially ongoing activity. The Dawn mission also found a high abundance of carbon in the regolith, interpreted as a mix of carbonates and amorphous carbon, as well as locally high concentrations of organic matter. Key findings from this review are as follows: (1) outside of the region of Occator crater, Ceres shows no geological evidence for conduits from the surface to the interior; and (2) considering the biological potential of Ceres' deep interior, a surface sample return mission should be considered Category V restricted, unless it can be demonstrated that evaporites sourced from Ceres' deep brine region, and recently exposed in Occator crater, have not been scattered to the rest of Ceres' surface; in that case, the probability of returning an unsterilized particle to an acceptably low value is to be determined by a future study.

Jupiter's polar aurora exhibits low brightness temperatures in Juno Microwave Radiometer (MWR) observations when the Juno spacecraft passes over the high-latitude region of the Northern Hemisphere. These cold features are observed predominantly at 0.6 GHz and show both long-term similar to ${\sim} $ hours and short-term changes over time, that is, spans less than the 30-s spacecraft spin period. The MWR "cold spot" observations are associated with polar ultraviolet emission features that are thought to originate from high energy electron precipitation into the Jovian high latitude atmosphere. The energetic electron precipitation produces strong absorptive characteristics at microwave frequencies due to the transient formation of high-density electron regions in the lower stratosphere. In this paper, we describe progress on the analysis of Juno MWR observations of the northern aurora and simulate the effects of heating and electron impact ionization processes due to high energy particle precipitation events in Jupiter's auroral ionosphere. Electron precipitation intensities at energies up to 10 MeV inferred from the Jupiter Energetic-Particle Detector Instrument (JEDI) and Ultraviolet Spectrograph (UVS) instruments are used as a Northern Hemisphere case study to understand the energy deposition and ionization processes in the lower stratosphere, and subsequently used to estimate the microwave and ultraviolet opacity of the auroral region. The northward progression of Juno's perijove during the mission reduces the overflight altitude and allows important insights into effects produced at different length scales with respect to the auroral oval.

We present evidence that Ariel's massive chasma-medial groove systems formed via spreading, where internally sourced material ascended and formed new crust. Evidence for this interpretation includes close alignment of offset faults and chasma margins during reconstruction, axial troughs bounded by raised rims, bowed-up chasma floors with marginal valleys, subparallel chasma floor ridges, and relatively young medial groove–bounding terrain. Ariel's medial grooves are among the youngest known Uranian moon geologic features and might be conduits to the interior and the source of NH-bearing species, CO, CO _2 , and other potential internally derived volatiles detected on the surface. While medial grooves are observable in Brownie and Kewpie Chasmata, our results indicate that these features are also present below Voyager 2 Imaging Science System image resolutions in Korrigan, Pixie, and Sylph Chasmata. Close flybys of Ariel with a Uranus orbiter are imperative to uncover the nature of these curious features and to gain insight into this moon's most recent geologic events.

The Venusian O(1S-1D) 5577 & Aring; "oxygen green line" has been an enigmatic feature of the Venusian atmosphere since its first attempted observation by the Venera spacecraft. Its first detection in 1999 and subsequent detections point to a unique auroral phenomena. However, the lack of (1D-3P) 6300 & Aring; "oxygen red line" emission suggests that the green line originates from deep in the ionosphere, much lower than current models predict. Here, we present 16 years of ground-based observations of the Venusian green line, comparing its behavior to the solar wind and spacecraft observations of the Venusian ionosphere. We find that all instances of green line emission occur during solar energetic particle (SEP) events, with a Matthews correlation coefficient of 0.93 between emission and the presence of SEPs. Coordinated observations between Venus Express and ground-based observatories show enhanced nightside ionospheric peak densities during the time of green line emission, with the lowest peak occurring at 115 km near local midnight. Such high density yet low altitude peaks suggest the presence of highly energetic particle precipitation. Initial modeling indicates >= ${\ge} $50 keV protons are needed to penetrate to such low altitudes. Comparisons of solar wind data confirm that such protons are present during all green line detections and nightside ionosphere enhancements. The association of SEP storms with green line emission and low nightside ionospheric peaks indicates that the green line is a unique global diffuse aurora, likely originating deep in the ionosphere and driven by proton precipitation, something that could be common for all non-magnetic planetary atmospheres.

JWST observations of Europa's leading hemisphere show excess CO2 over chaos terrains [1, 2] where the subsurface ocean is likely to have breached the ice shell. Analysis of the 3.5-µm hydrogen peroxide (H2O2) absorption band reveals elevated amounts of H2O2 in these chaos regions. Peroxide abundance scales with CO2 abundance, presenting a strong pixel-level linear correlation, particularly with the υ3 CO2 feature at 4.27 mm (Figure 1).New laboratory experiments [3] motivated by these observations show that trace inclusions of CO2 can substantially inflate the radiolytic peroxide yield, more so than in pure water ice. We considered various mechanisms by which CO2 boosts H2O2 synthesis and developed an analytical model to quantify the dependence of peroxide enhancement on CO2 abundance [3]. These experiments support the hypothesis that endogenic CO2 may amplify H2O2 synthesis in the Tara and Powys Regiones when processed by Jupiter's magnetospheric particles. We combine the CO2-enhanced H2O2 yields with the energy dose delivered by the magnetospheric particles onto the leading hemisphere [4, 5] to generate a peroxide distribution map to compare with the observed distribution. Our results highlight the intricate interplay of Europa’s interior ocean, geologic activity, and precipitating radiation in shaping surface chemistry, boosting the synthesis of molecules vital for habitability.Figure 1: Exploring correlations between Europa’s peroxide and CO2 absorption. Integrated H2O2 band area against each of the three CO2 band areas. Grey data points are individual pixel values, while red points are binned data. The red lines are linear fits to these binned datasets. The strongest linear correlation, quantified by Pearson’s correlation coefficient, occurs between the peroxide and the 4.27 µm CO₂ absorptions.The rapid transport of peroxide to the subsurface ocean via brine-percolated conduits [6] has strong implications for Europa's habitability. The mixing of these oxidants with reduced seawater, derived from geochemical cycling through the porous seafloor, could generate ‘redox potential’, supplying chemical energy that putative life forms may utilize to sustain metabolism, cellular maintenance, and reproduction [7]. These JWST observations combined with laboratory measurements set the stage for detailed mapping of CO2 (via its 2.7 and ~ 4.2 - 4.3 µm absorptions), H2O2 (via its 3.5 µm absorption) and possibly CHO organics with MISE (Europa Clipper) and MAJIS (Juice) at finer spatial scales to advance our understanding of Europa’s surface and subsurface composition and chemistry.References:[1] Villanueva, G. L., et al. 2023, Science, 381, 1305. [2] Trumbo, S. K., & Brown, M. E., 2023, Science, 381, 1308. [3] Mamo, B. et al., 2025, Planetary Science Journal, submitted. [4] Nordheim, T. A., et al., 2022, Planetary Science Journal, 3, 5. [5] Nordheim, T. A., 2018, Nat. Astro., 2, 673-679. [6] Hesse, M.A., et al., 2022, Geophysical Research Letters, 49, 5. [7] Hand, K., et al., 2007, Astrobiology, 7, 1006-1022.

We present the results of the implantation of energetic sulfur ions in icy samples (H2O:C3H8 and H2O:C3H7OH) in temperature conditions relevant to Europa and other Jovian satellites. The surface of the Jovian moons experiences an intense bombardment of energetic particles, including sulfur ions over a large range of energy[1][2]. Any organic matter emplaced onto the surface from the internal ocean would be processed by this bombardment, with the possibility for sulfur to be included into the resulting products. As a results, the future space missions to the galileans moons (NASA’s Europa Clipper and ESA’s JUICE) may encounter such processed organic matter, which will complicate the characterization of the organic matter from the interior. The MASPEX [3] and SUDA [4] instruments in particular will get the opportunity to characterize the organic matter on Europa’s surface with unprecedented sentitivity and mass resolution.Here, in temperature conditions relevant to Europa (80 K), we investigate the composition of the organic residues generated by the irradiation of a water:propane ice and a water:propanol ice with a 105 keV S7+ ion beam. Propane is the simplest alkane that can be condensed at a temperature relevant to Europa’s surface, and propanol is the corresponding alcohol. The irradiated samples were slowly warmed up to 300 K to sublimate the volatiles and leave the refractory organic residues. The residues were analyzed with Ultra-High Resolution Mass Spectrometry using two ionization techniques (laser desorption and electrospray).The analysis of the residue from the irradiation of the water:propane ice shows a very diverse (2000 + unique formulas) organic matter, with heavy molecules (up to m/z>800). We find large numbers of aromatic CH species (Figure 1, left) and oxygen-rich, less aromatic species, depending on the ionization technique used. Organosulfurs are found both in CHS form and CHOS; they are minor both in number and intensity, but demonstrate the possibility of forming organosulfurs in the surface conditions of Europa through sulfur implantation with any organic. [5]The residue resulting from the water:propanol sample, as seen with laser desorption is very similar, without any noticeable difference between the number and intensity of O-bearing annotations, or aromaticity (Figure 1). Twice as many CHS annotations are found in the water:propanol residue compared to water :propane.The dose used in our study represents a geologically short time on the surface of Europa (from a few days to a few thousands of year, depending on the region considered). This indicates that the properties of organic precursors may swiftly be erased by radiation processing on the surface. Future work with different doses and precursor species will better constrain how radiation chemistry alters organic signatures on the surface. [1] J.F. Cooper, et al.,. Icarus, 149(1), 133-159. (2001)[2] C. Paranicas et al.,., Europa. U. Arizona Press, Tucson, 529 (2009)[3] Waite Jr, J. H., et al. Space Science Reviews 220.3 (2024): 30.[4] Goode, W., et al. Planetary and Space Science, 227, 105633. (2023).[5] Bouquet, A., et al. The Planetary Science Journal, 5(4), 102 (2024).Fig1 : #C vs DBE (Double Bond Equivalent) of the annotations obtained by Laser Desorption Ionization – Fourier Transform Ion Cyclotron Resonance (LDI-FTICR) applied to the residue of the S-implanted Water :Propane Ice (left) and Water :Propanol Ice (right).

We present a feasibility study for passive sounding of Uranian icy moons using Uranian Kilometric Radio (UKR) emissions in the 100 - 900 kHz band. We provide a summary description of the observation geometry, the UKR characteristics, and estimate the sensitivity for an instrument analogous to the Cassini Radio Plasma Wave Science (RPWS) but with a modified receiver digitizer and signal processing chain. We show that the concept has the potential to directly and unambiguously detect cold oceans within Uranian satellites and provide strong constraints on the interior structure in the presence of warm or no oceans. As part of a geophysical payload, the concept could therefore have a key role in the detection of oceans within the Uranian satellites. The main limitation of the concept is coherence losses attributed to the extended source size of the UKR and dependence on the illumination geometry. These factors represent constraints on the tour design of a future Uranus mission in terms of flyby altitudes and encounter timing.

The Cassini spacecraft observed that Saturn's moon Enceladus possesses a series of jets erupting from its South Polar Terrain. Previous studies of in situ data collected by Cassini's Ion and Neutral Mass Spectrometer (INMS) have identified H$_2$O, CO$_2$, CH$_4$, NH$_3$, and H$_2$ within the plume of ejected material. Identification of minor species in the plume remains an ongoing challenge, owing to the large number of possible combinations that can be used to fit the INMS data. Here, we present the detection of several new compounds of strong importance to the habitability of Enceladus, including HCN, C$_2$H$_2$, C$_3$H$_6$, and C$_2$H$_6$. Our analyses of the low velocity INMS data, coupled with our detailed statistical framework, enable discrimination between previously ambiguous species in the plume by alleviating the effects of high dimensional model fitting. Together with plausible mineralogical catalysts and redox gradients derived from surface radiolysis, these compounds could potentially support extant microbial communities or drive complex organic synthesis leading to the origin of life.

The surface of Ganymede exhibits diversity in composition, interpreted as indicative of geological age differences between dark and bright terrains. Observations from Galileo and Earth-based telescopes have revealed the presence of both water ice and non-ice material, indicative of either endogenic or exogenic processes, or some combination. However, these observations attained a spatial resolution that was too coarse to reveal the surface composition at a local scale. Here we present the high-spatial-resolution infrared spectra of Ganymede observed with the Jovian InfraRed Auroral Mapper onboard the National Aeronautics and Space Administration’s Juno spacecraft during a close flyby that occurred on 7 June 2021. We found that at a pixel resolution <1 km, the surface of Ganymede exhibits signatures diagnostic of hydrated sodium chloride, ammonium chloride and sodium/ammonium carbonate, as well as organic compounds, possibly including aliphatic aldehydes. Carbon dioxide shows up mostly at trailing longitudes. The composition and spatial distribution of these salts and organics suggest that their origin is endogenic, resulting from the extrusion of subsurface brines, whose chemistry reflects the water–rock interaction inside Ganymede.

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-micron absorption bands resulting from solid-state 12CO2, 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 H2O mixed with carbonaceous compounds. We detected CO2 rovibrational emission lines between 4.2 and 4.3 microns over both hemispheres, confirming the global presence of CO2 gas in Callisto's tenuous atmosphere. These results represent the first detection of CO2 gas over Callisto's trailing side. The distribution of CO2 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-micron absorption band that likely results from solid-state 13CO2. A prominent 4.57-micron absorption band that might result from CN-bearing organics is present and significantly stronger on Callisto's leading hemisphere, unlike 12CO2, suggesting these two spectral features are spatially anti-associated. The distribution of the 4.57-micron 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 (OCS), 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.

Icy bodies are the most numerous and diverse bodies in the Solar System, but only a few have been visited or will be visited by a space probe. The Galilean satellites are one of those, especially Ganymede which is the primary target of the future L-class mission JUICE (launch scheduled in 2022) in ESA’s Cosmic Vision programme. Ganymede's surface visually exhibits an important geological diversity, with young bright areas to older dark terrains. This diversity also expresses itself through the moon’s surface composition, which was studied extensively in situ by the NIMS instrument of the Galileo mission (NASA) in the late 90s; like the majority of giant planet satellites, Ganymede's surface is dominated by H2O-ice and some non-icy components, very likely hydrated salts based on the distorted shape of the spectral signatures (McCord et al., 2001). However, this binary composition has been obtained with a spectral sampling (~25 µm) not allowing to detect specific absorptions for the non-icy materials, thus not allowing their identification. Hence, many questions about Ganymede’s surface composition remain unanswered while important technical advances have been made since. In preparation of the JUICE mission, and specifically of the near-infrared imaging spectrometer MAJIS of the JUICE mission, a ground-based campaign was performed using an instrument with a much finer, i.e. better, spectral sampling: SINFONI (SINgle Faint Object Near-IR Investigation). SINFONI is installed on the UT4 of the Very Large Telescope (VLT hereafter) at the European Southern Observatory (ESO hereafter) in Chile. It combines one adaptive optics module and an integral field spectrometer operating in the near-infrared covering from the beginning of the J-band (~1.1 µm) to the end of the K-band (~2.45 µm). Here we present the results derived from the analysis and the modeling of four observations acquired at different dates, from October 2012 to March 2015, all covering the 1.45 – 2.45 µm wavelength range with a spectral resolution about 0.5 µm and a spatial sampling of 12.5 x 12.5 mas2. These results were recently published in Icarus (Ligier et al., 2019). The first result we obtained concerns the physical properties of Ganymede’s surface. Indeed, the data reduction process highlights that the Lambertian model is not sufficient to remove the photometric effects due to observations geometry. Instead, the Oren-Nayar model (Oren & Nayar, 1994), which generalizes the Lambertian law for rough surfaces, produces excellent results where no inclination residuals are observed up to inclination angles around 65°. The quality of the photometric correction is thus used as proxy to infer Ganymede’s surface roughness: from 16° ± 6° to 21° ± 6° depending on the observations. Then, concerning the surface composition of the moon, our modeling confirms that it is dominated by H2O-ice, predominantly the crystalline form. The abundance maps of the ice show two main patterns: (1) a latitudinal gradient in terms of abundance, with large polar caps, and (2) a latitudinal gradient in terms of grain size, where the smaller grains (>50 µm) are located at the highest latitudes, showing a sharp transition around ±35°N coinciding with the transition between open and closed field lines of Ganymede’s own magnetic field (figure 1a). Ice sublimation explains this distribution, redistributing H2O-ice from the “hot” equator to the colder poles, very likely redeposited as finer grains. Apart from the ice, another major compound is required to fit Ganymede’s spectra: a darkening agent. Similarly to previous studies, this darkening agent could not be identified, but we were able to provide new constraints on it. First of all, this unknown material cannot be organic matter since its reflectance level, about 0.25, is more or less five times higher than that of organic matter. Instead, the reflectance level suggests a silicate-type material, as already mentioned in a previous study about Callisto (Calvin & Clark, 1991). Its abundance map shows the highest abundances (up to 0.85) at equatorial latitudes in the trailing hemisphere (figure 1b). The well-known surface sputtering engendered by Jupiter’s magnetosphere is the simplest process to explain such distribution. Even with the magnetic field of the moon, it is possible for corotating singly-charged ions to become neutralized near the moon and continue to the surface as neutrals, sputtering mostly around the trailing apex. Last but not least, our study highlights the necessity of secondary species, i.e. >10% overall, to better fit the measurements: sulfuric acid hydrate and salts, likely sulfates and chlorinated. While the sulfuric acid hydrate is, like H2O-ice, mostly located at high latitudes (figure 1c), the abundance map of the salts shows a heterogeneous distribution which seems neither related to the Jovian magnetospheric bombardment nor craters (figure 1d). These species are mostly detected on bright grooved terrains surrounding darker areas. Endogenous processes, such as freezing of upwelling fluids going through the moon’s ice shell, may explain this heterogeneous distribution.

Europa’s surface is exposed to a constant flow of plasma from its ionosphere and Jupiter’s magnetosphere. As these particles flow onto the surface, an electrostatic surface potential forms. We investigate the electrostatic charging of Europa’s surface using 3D particle-in-cell simulations. We find that surface potentials on Europa vary from −14 to −52 V. The predicted surface potentials vary as a function of location on Europa, illumination conditions, plasma environment, and surface properties. We reveal that the ionosphere has a significant “dampening effect,” limiting the formation of large negative surface potentials. Furthermore, we find that secondary emission is a key factor in determining the surface charge on Europa. We discuss how such potentials may be remotely detected by upcoming missions, such as Europa Clipper and JUICE. Our results may also be of use in the design of future missions to Europa’s surface, such as landers and other robotic explorers.

We performed experiments of implantation of energetic sulfur ions (105 keV) into 2:1 water:propane ices at 80 K and analyzed the resulting refractory organic matter with ultrahigh-resolution mass spectrometry. Our goal was to characterize the organic matter processed in the surface conditions of Europa, where it would receive a heavy flux of energetic particles, including sulfur ions, and determine whether organosulfurs could be formed in these conditions, using the simplest alkane that can exist in solid form on Europa's surface. We find that the produced organic matter contains a large variety of both aliphatic and aromatic compounds (several thousand unique formulae), including polycyclic aromatic hydrocarbons (PAHs), with masses up to 900 amu. A large number of aromatic hydrocarbons is found along with oxygenated, mostly aliphatic, compounds. Organosulfurs are found in both CHS and CHOS form, demonstrating they can be formed from any organic compound through sulfur implantation. These organosulfurs' properties (aromaticity, mass) appear similar to the rest of the organic matter, albeit their low quantity does not allow for a thorough comparison. Our results have implications for the type of refractory organic matter that could be observed by the JUICE and Europa Clipper space missions and how the surface of Europa could generate complex organics, including PAHs and organosulfurs, that could then enrich the subsurface ocean. In particular, they indicate that a large diversity of organic matter, including organosulfurs, can be formed from simple precursors in a geologically short time frame under the ion flux that reaches Europa.

Images from the Voyager 2 mission revealed the small Uranian satellite Miranda to be a complex, dynamic world. This is exemplified by signs of recent geological activity, including an extensive fault system and the mysterious coronae. This has led to speculation that Miranda may have been tectonically active within the geologically recent past and could have hosted a subsurface liquid water ocean at the time. In this work, we aim to constrain the thickness ranges for the ice shell and potential subsurface ocean on Miranda. Here, we present the results for our geological mapping of craters, ridges, and furrows on the surface. We also present the results for our comparison of the geographic distribution of these features to the predicted geographic distribution of maximum tidal stress based on stress models. We model eccentricity tidal stress, ice shell thickening stress, true polar wander stress, and obliquity tidal stress and compare the predicted surface stress pattern for each to what pattern can be inferred from the surface geology. Our results show that a thin crust (<= 30 km) is most likely to result in sufficient stress magnitude to cause brittle failure of ice on Miranda's surface. Our results also suggest the plausible existence of a >= 100 km thick ocean on Miranda within the last 100-500 million yr. This has implications for the dynamical history of Miranda and its status as a potential ocean world.

The Uranian moon Ariel exhibits a diversity of geologically young landforms, with a surface composition rich in CO _2 ice. The origin of CO _2 and other species, however, remains uncertain. We report observations of Ariel’s leading and trailing hemispheres, collected with NIRSpec (2.87–5.10 μ m) on the James Webb Space Telescope. These data shed new light on Ariel's spectral properties, revealing a double-lobed CO _2 ice scattering peak centered near 4.20 and 4.25 μ m, with the 4.25 μ m lobe possibly representing the largest CO _2 Fresnel peak yet observed in the solar system. A prominent 4.38 μ m ^13 CO _2 ice feature is also present, as is a 4.90 μ m band that results from ^12 CO _2 ice. The spectra reveal a 4.67 μ m ^12 CO ice band and a broad 4.02 μ m band that might result from carbonate minerals. The data confirm that features associated with CO _2 and CO are notably stronger on Ariel’s trailing hemisphere compared to its leading hemisphere. We compared the detected CO _2 features to synthetic spectra of CO _2 ice and mixtures of CO _2 with CO, H _2 O, and amorphous carbon, finding that CO _2 could be concentrated in deposits thicker than ∼10 mm on Ariel’s trailing hemisphere. Comparison to laboratory data indicates that CO is likely mixed with CO _2 . The evidence for thick CO _2 ice deposits and the possible presence of carbonates on both hemispheres suggests that some carbon oxides could be sourced from Ariel’s interior, with their surface distributions modified by charged particle bombardment, sublimation, and seasonal migration of CO and CO _2 from high to low latitudes.

The magnetospheric systems of ice giants, as the ideal and the unique template of a typical class of exoplanets, have not been sufficiently studied in the past decade. The complexity of these asymmetric and extremely dynamic magnetospheres provides us a great chance to systematically investigate the general mechanism of driving the magnetospheres of such common exoplanets in the Universe, and the key factors of influencing the global and local magnetospheric structures of this type of planets. In this paper, we discuss the science return of probing magnetospheric systems of ice giants for the future missions, throughout different magnetospheric regions, across from the interaction with upstream solar wind to the downstream region of the magnetotail. We emphasize the importance of detecting the magnetospheric systems of ice giants in the next decades, which enables us to deeply understand the space enviroNMent and habitability of not only the ice giants themselves but also the analogous exoplanets which are widely distributed in the Universe.

The moons of Uranus have only been visited once by Voyager 2 during its 1986 flyby. Earth-based telescopic observations show a spectral signature of carbon dioxide ice on the Uranian moons Ariel, Umbriel, Titania, and Oberon, with a somewhat higher abundance on their trailing hemispheres. The inner major moon Ariel exhibits the strongest carbon dioxide ice absorption bands, which then decrease in strength with increasing orbital distance from Uranus, with the outer major moon Oberon exhibiting the weakest absorption bands. Previous work has suggested that these hemispherical and radial trends result from radiolytic production of carbon dioxide ice from interactions between the moons' surfaces and charged particles trapped in Uranus' magnetosphere. Here, we use volatile transport modeling to characterize a possible migration cycle of carbon dioxide on Ariel. We find that carbon dioxide is readily mobilized toward Ariel's equator, and that existing topography such as canyons are locations of favorable deposition for carbon dioxide ice. We predict the presence of carbon dioxide ice deposits on the floors of Ariel's canyons. Our work suggests two possible classes of sources of carbon dioxide: an active source, which may be consistent with either radiolytic production from Uranus' magnetosphere or outgassing from Ariel's interior, or an ancient source that produced CO2 that still exists in stable canyon deposits. A future Uranus orbiter could determine which hypothesis is most likely, or if carbon dioxide could be found both in the form of ice deposits on the surface and in a global exosphere. Uranus' moons have only been visited once by the Voyager 2 spacecraft in 1986. Observations from telescopes on Earth show that there is carbon dioxide ice on four of the five largest Uranian moons, but it is mostly concentrated on one hemisphere. Previous work hypothesizes that this carbon dioxide ice could be made by the moons' surfaces interacting with electrons and ions trapped in Uranus' magnetic field. We tested that hypothesis using a model for Ariel, the moon with the strongest evidence for carbon dioxide ice. We find that carbon dioxide ice will move quickly away from Ariel's poles and toward the equator. Because carbon dioxide moves quickly, our results suggest that carbon dioxide could either be actively produced or uncovered on the surface or could be anciently formed from material coming from Ariel's interior; or both mechanisms could source the carbon dioxide. We also find that carbon dioxide ice deposits are likely on the floors of the canyons that were visible in Voyager 2 images of Ariel's surface. The Uranian moons show a spectral signature of carbon dioxide ice (Ariel most strongly) preferentially on their trailing hemispheres We find that carbon dioxide ice is transported toward Ariel's equator, and both an active and ancient source of carbon dioxide is plausible We predict carbon dioxide deposits on the floors of Ariel's canyons, which could be detected by a future Uranus orbiter