Richard J. Cartwright

James Webb Space Telescope (JWST) observations of Europa’s leading hemisphere reveal enhanced CO ₂ abundances over equatorial chaos terrains where the subsurface ocean is thought to have breached the ice shell. Hydrogen peroxide, synthesized radiolytically by Jovian magnetospheric charged particles impinging on Europa’s ice, is also elevated in these geologically active regions, spatially coinciding with CO ₂ . This correlation implicates CO ₂ in H ₂ O ₂ synthesis, consistent with laboratory experiments showing increased radiolytic peroxide yields in carbon-bearing ices. Our radiolysis model – which incorporates charged-particle precipitation through electromagnetic fields accounting for Europa’s interaction with Jupiter’s magnetosphere – predicts enhanced H ₂ O ₂ on the leading hemisphere equatorial regions. The relative dearth of energetic electrons in this region shields peroxide from destruction, leaving a notably higher abundance towards the leading apex compared to the mid-latitude regions or the trailing side. Integrating the inferred CO ₂ abundance and the associated boost in peroxide yield, we show that ocean-derived CO ₂ acts as a multiplier, further elevating H ₂ O ₂ concentrations within the fractured surfaces of Tara and Powys Regiones. Together, these results imply that geologic resurfacing at Europa’s chaos terrains and precipitating radiation conspire to contribute to the excess peroxide observed by JWST, with endogenic CO ₂ amplifying oxidant production in these potentially ocean-linked regions.

We present maps of H ₂ O, CO ₂ , and a 4.57 µ m spectral feature across Callisto’s surface observed using the James Webb Space Telescope (JWST). H ₂ O ice was mapped by measuring band parameters of the 3.1 µ m Fresnel peak across the leading and trailing hemispheres under a simplified assumption of crystalline ice. We update the CO ₂ solid-phase, CO ₂ gas, and 4.57 µ m feature band depth maps originally presented in R. J. Cartwright et al. with a new JWST observation of Callisto centered on Valhalla, the largest multi-ring impact basin in the solar system. Our H ₂ O ice map shows that the Fresnel peak on the trailing hemisphere exhibits a bullseye pattern that is weaker at low latitudes, and on the leading hemisphere its strength is associated with impacts. This dichotomy is possibly related to the Jovian magnetospheric plasma impinging on the trailing hemisphere. Our solid-phase CO ₂ map reveals an enhancement in the vicinity of the Lofn/Heimdall impact craters, a region that may be the largest reservoir of nonradiolytic CO ₂ on Callisto’s surface. The gas-phase CO ₂ exhibits a patchy spatial distribution and does not clearly correlate with solid CO ₂ .

The Uranian moons Ariel, Umbriel, Titania, and Oberon are enriched in CO ₂ mixed with CO, but the origin(s) of these carbon oxides, be they primarily native or radiolytic, remain(s) uncertain. Using data collected by NIRSpec on the James Webb Space Telescope (JWST), we measured the spectral signature of CO ₂ and other carbon oxides to help disentangle these hypotheses. Through comparison to laboratory data, we find that many of the detected spectral features are consistent with CO ₂ ice, including ¹² CO ₂ scattering peaks (4.15–4.26 μ m), multilobe ¹³ CO ₂ bands (4.35–4.43 μ m), and CO ₂ biphonon and triphonon modes (4.80–5.25 μ m). Our measurements show that CO ₂ and CO are concentrated on the trailing hemispheres of the inner moons Ariel and Umbriel, potentially supporting a radiolytic production hypothesis, consistent with prior ground-based results. However, many of the identified spectral features are only observed in thick crystalline ice deposits measured in the laboratory, which may be difficult to form via radiolysis of carbon-bearing material mixed in icy regoliths. Similarly, the data exhibit weak 4.02 and 4.40 μ m bands, hinting at the presence of carbonate minerals and ¹³ CO ₂ clathrates, respectively, possibly formed in the interiors of these moons. Furthermore, JWST has revealed that CO ₂ is widespread at Uranus, present in its system of rings, ring moons, and irregular satellites, consistent with its largest moons accreting CO ₂ and other carbon oxides from the Uranian subnebula. We conclude that exposed carbon oxides are potentially native, with their surface distributions shaped by charged particle irradiation and seasonal sublimation–condensation cycles.

Models of our solar system’s protoplanetary disk account for processes such as the infall of water–ice-rich grains from the surrounding molecular cloud, the reprocessing of some infalling water–ice in the hot inner disk, and water’s outward migration in the disk. These models predict deuterium abundance in water as a function of heliocentric distance. The James Webb Space Telescope (JWST) enables us to test these models by measuring the abundance of deuterium on icy outer solar system bodies through spectroscopic observations of the semiheavy water (HDO) band near 4.1 μ m. However, a hurdle to measuring deuterium abundances from JWST spectra is the lack of optical constants for HDO. We present the separated contributions of HDO and H ₂ O to the optical constants of crystalline water–ice that contains both isotopologues. In addition, we combine these effective optical constants, a radiative transfer model, and a JWST spectrum of the Uranian satellite Titania to measure its deuterium abundance in water, finding D/(H+D) = (2.8 ± 0.5) × 10 ⁻⁴ in agreement with the model by L. Yang et al. Using a simple model, we estimate that most of Titania’s water originated from thermally processed inner-disk water, and only a minor portion came from inherited molecular-cloud water. By combining our Titania measurement with Saturnian satellite and comet measurements in the literature, we suggest that outer-satellite water came from a more homogeneous reservoir than comets, and perhaps accreted over a shorter time interval than comets. Furthermore, Titania’s deuterium abundance suggests that it formed in a lower-temperature, hydrogen-poor circumplanetary disk rather than a higher-temperature, hydrogen-rich disk.

Origins, Worlds, and Life: Planetary Science and Astrobiology in the Next Decade identified a Uranus Orbiter and Probe as the highest-priority strategic mission for the decade 2023–2032, as it enables broad cross-disciplinary science in the largely unexplored Uranian system. The mission architecture evaluated by the Decadal Survey was a singular proof of concept demonstrating that a moderately instrumented mission could deliver Decadal-priority science with a reduced cost and risk posture by leveraging existing technologies to the maximum extent possible. With revised assumptions since the Decadal, we have explored a large trade space including launch vehicles, propulsion options, cruise trajectories, available power sources, viable concept of operations, and science data return for later launch dates without a Jupiter gravity assist. The most repeatable trajectory solutions employ either a commercially derived solar electric propulsion (SEP) transfer stage or the availability of a more capable launch vehicle under development, such as the SpaceX Starship. Orbit insertion has been moved farther from Uranus to acknowledge the remaining uncertainty in Uranian ring structure. A streamlined, SEP-adaptable, orbiter design was developed using two Next Gen Radioisotope Thermoelectric Generators, and the probe design was matured, reducing the entry gravitational acceleration, and assuming the largest Decadal-recommended payload to provide margin for future instrument selections. With this updated design, we also constructed a detailed concept of operations for three representative science cases, returning 13–15 Gbit of science data and spacecraft telemetry per ∼34 day orbit.

Red spectral slopes (i.e. increasing reflectance with increasing wavelength) and featureless 0.5–2.5 μ m spectra are often associated with the presence of organic material, and there is a sense that the redder the slope, the more organic material is present and the more distant the formation location. This has led to the D-class asteroids, which are the reddest asteroid spectral type, being used as proxies for outer-solar-system material when considering material transport. The asteroids 269 Justitia and 203 Pompeja have been identified as the reddest main-belt asteroids, a distinction that follow-up observations have confirmed for Justitia. This has been used as evidence that Justitia is a transported trans-Neptunian object. We observed Justitia and Pompeja during their 2022 apparitions to determine their compositions from measurements in the 3 μ m region. We found that other than spectral slope, Justitia’s spectrum is a very good match to typical aqueously altered carbonaceous chondritic material and to C-complex asteroids like Bennu and Polana, but very poor matches to spectra of most D-class asteroids, Jovian Trojans and irregular satellites, and Centaurs. We also found that Pompeja’s spectrum is consistent with Justitia’s, though of lower quality. While we do not know what is causing Justitia’s steep spectral slope, its composition appears to be consistent with common carbonaceous chondrites, and there is no need to invoke a separate formation location. It is not evident that Justitia, or any particularly red-sloped asteroid, can have its formation location inferred from spectral slope alone.

We present an analysis of ground-based visible and near-infrared wavelength (VIS, ∼0.4–0.9 μ m) reflectance spectra of the four largest Uranian satellites, utilizing observations with multiple telescopes, collected near Uranian equinox and in northern summer (2002–2024). These data have much higher spectral resolution and signal-to-noise ratios compared to previously published optical spectra of the Uranian moons, collected primarily in the 1980s and 1990s. The higher signal-to-noise ratios and longitudinal coverage of these new data allowed us to determine that the Uranian satellites exhibit distinct spectral slope variations across the VIS, supporting previous findings that the leading hemispheres of Titania and Oberon are redder than their respective trailing hemispheres. We find that the northern leading hemisphere of Titania appears to be redder than Oberon, and that Titania may have a larger leading/trailing asymmetry in reddening on its northern hemisphere compared to the other three large moons. We also conducted a sensitive search for subtle absorption features, but found no reliable evidence of broad mineral absorption bands, condensed O ₂ , or other possible products of radiolytic processing; aside from the spectral slope, the spectra of the Uranian moons appear to be featureless in the visible wavelength range.

The imaged portion of Umbriel's surface is dark and cratered, suggesting limited geologic activity. However, bright deposits occupying the Wunda impact crater may be of endogenic origin, similar to proposed cryovolcanic sources for fresh bright material occupying Occator crater on Ceres. Here, we model the formation of Wunda using iSALE‐2D. Our goal is to determine whether Wunda's inferred morphology is consistent with the interior structure predicted for Umbriel and whether Wunda's interior might originate from impact‐induced cryovolcanism and/or was sourced from a subsurface ocean. We find that, if Wunda is indeed a complex crater, as coarsely resolved imagery suggests, Umbriel's ice shell may have been much thinner (50 km) and/or warmer (240 K) than predicted at present or subject to significant structural/compositional differences, such as abundant volatiles. These results help assess the thermal evolution of the Uranian satellites as potential ocean worlds.

We observed Io with the James Webb Space Telescope (JWST) NIRSpec/Integral Field Unit (1.0–5.3 μm, ) in August 2023 while the satellite was in eclipse. Thermal emission from Kanehekili Fluctus is consistent with the cooling of lava flows after a vigorous eruption in November 2022. At Loki Patera, after a new brightening event was detected in November 2022, the lava lake was in a quiescent state, as expected from previous analyses. We mapped the SO emission band at 1.707 μm, and detected, for the first time, [SI] emission lines at 1.082 and 1.131 μm. The SO emissions are concentrated above Kanehekili Fluctus, and in two regions in the northern hemisphere. The disk‐averaged brightness is 14.5 kR. The emissions are sourced from SO molecules ejected from 1,500 to 1,700 K vents in an excited state, with a typical SO column density above the northern hemisphere of . Sulfur emissions are distributed homogeneously across a band in the northern hemisphere. The disk‐averaged total brightness is 5.6 kR, versus 9.65 kR in the north. The emissions are produced through direct electron impact excitation by 4 eV electrons in the torus (density 2,500 ) penetrating the atmosphere, and require the atmosphere to be hot (1,700 K) to populate the upper levels before excitation. The sulfur column density over the northern hemisphere is . These same parameters can explain recent 0.7725‐m observations, as well as the 147.9‐nm multiplet emissions observed with HST‐STIS 20 years earlier. This suggests a quite stable system over decades‐long timescales.