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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.

Comets are frozen remnants of our solar system’s formation, and comparing their chemical composition to that of planet-forming systems can reveal crucial insights about our origins, potentially answering one of the most challenging questions in planetary science, i.e., whether cometary material was mainly inherited from the protosolar nebula or reprocessed during the solar system formation. Here we provide the first statistical analysis of methanol, formaldehyde, and ammonia abundances in 35 comets and 11 protostellar solar analogs and planet-forming disks. We show that comets from different dynamical families have comparable compositions on average, implying that their chemistry is preserved even after formation. While abundances retrieved from infrared and (sub)millimeter ground-based observations are in agreement, there are significant differences with those obtained via mass spectroscopy for 67P/Churyumov–Gerasimenko, target of the ESA-Rosetta mission; we discuss the implication of relying solely on the latter data for comparisons with disk abundance ratios. Finally, we find a significant difference in the [CH _3 OH]/[H _2 CO] ratio in comets observed within or farther than 1 au from the Sun, suggesting that temperature-activated mechanisms can enhance the H _2 CO production in the coma; this bias can strongly influence our understanding of comet chemistry in the context of planet formation. When compared to planet-forming systems, the [CH _3 OH]/[H _2 CO] and [NH _3 ]/[CH _3 OH] molecular abundance ratios in comets are consistent with those measured in Class 0 hot corinos and in the inner regions of Class II disks, hence suggesting an inheritance scenario.

Radiative transfer (RT) models are critical in the interpretation of exoplanetary spectra, in simulating exoplanet climates, and when designing the specifications of future flagship observatories. However, most models differ in methodologies and input data, which can lead to significantly different spectra. In this paper, we present the experimental protocol of the Modeling Atmospheric Lines By the Exoplanet Community (MALBEC) project. MALBEC is an exoplanet model intercomparison project that belongs to the Climates Using Interactive Suites of Intercomparisons Nested for Exoplanet Studies framework, which aims to provide the exoplanet community with a large and diverse set of comparison and validation of models. The proposed protocol tests include a large set of initial participating RT models, a broad range of atmospheres (from hot Jupiters to temperate terrestrials), and several observation geometries, which would allow us to quantify and compare the differences between different RT models used by the exoplanetary community. Two types of tests are proposed: transit spectroscopy and direct imaging modeling, with results from the proposed tests to be published in dedicated follow-up papers. To encourage the community to join this comparison effort and as an example, we present simulation results for one specific transit case (GJ-1214 b), in which we find notable differences in how the various codes handle the discretization of the atmospheres (e.g., sub-layering), the treatment of molecular opacities (e.g., correlated- k , line-by-line) and the default spectroscopic repositories generally used by each model (e.g., HITRAN, HITEMP, ExoMol).

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.

The extraordinary 2021 September–October outburst of Centaur 29P/Schwassmann–Wachmann 1 afforded an opportunity to test the composition of primitive Kuiper disk material at high sensitivity. We conducted nearly simultaneous multiwavelength spectroscopic observations of 29P/Schwassmann–Wachmann 1 using iSHELL at the NASA Infrared Telescope Facility (IRTF) and nFLASH at the Atacama Pathfinder EXperiment (APEX) on 2021 October 6, with follow-up APEX/nFLASH observations on 2021 October 7 and 2022 April 3. This coordinated campaign between near-infrared and radio wavelengths enabled us to sample molecular emission from a wealth of coma molecules and to perform measurements that cannot be accomplished at either wavelength alone. We securely detected CO emission on all dates with both facilities, including velocity-resolved spectra of the CO ( J = 2–1) transition with APEX/nFLASH and multiple CO ( v = 1–0) rovibrational transitions with IRTF/iSHELL. We report rotational temperatures, coma kinematics, and production rates for CO and stringent (3 σ ) upper limits on abundance ratios relative to CO for CH _4 , C _2 H _6 , CH _3 OH, H _2 CO, CS, and OCS. Our upper limits for CS/CO and OCS/CO represent their first values in the literature for this Centaur. Upper limits for CH _4 , C _2 H _6 , CH _3 OH, and H _2 CO are the most stringent reported to date, and are most similar to values found in ultra CO-rich Oort cloud comet C/2016 R2 (PanSTARRS), which may have implications for how ices are preserved in cometary nuclei. We demonstrate the superb synergy of coordinated radio and near-infrared measurements, and advocate for future small-body studies that jointly leverage the capabilities of each wavelength.

We measured the chemical composition of comet C/2021 A1 (Leonard) using the long-slit echelle grating spectrograph iSHELL/IRTF on 2021 December 20 and on 2022 January 8 and 9. We sampled 11 primary volatiles (H _2 O, HCN, NH _3 , CO, C _2 H _2 , C _2 H _6 , CH _4 , CH _3 OH, H _2 CO, OCS, and HCl) and three product species (CN, NH _2 , and OH) and retrieved their molecular abundances, which can serve as important cosmogonic indicators. The abundance ratios, relative to water, of almost all trace volatiles appear to be depleted relative to reference values, with methanol abundance among the lowest observed in a comet. The observed stronger depletion of CH _3 OH, relative to CO, CH _4 , and C _2 H _6 , could be evidence of an interstellar medium (ISM) chemistry signature in comet/Leonard ices. Both the detection of HCl and the detection of OCS support the idea of interstellar origin for comet/Leonard ices, since they are preferentially formed via solid-phase interstellar chemistry and are then found depleted in dense molecular clouds and protoplanetary disks, suggesting that their abundances in comets might retain a signature from the ISM era. The comet also revealed a complex outgassing pattern, with volatiles largely shifted toward the sunward direction, relative to the dust profiles that appeared centered on the nucleus-centric position. Here we present emission profiles measured along the Sun–comet line for brightest lines of H _2 O, HCN, C _2 H _6 , and CO, and we show that they follow the release of water in similar fashion, interpreting this as indication of a not strict relationship between polar and apolar ices.