We present observations of the Uranian outer ring system at near-infrared and visible wavelengths. Observations with the Keck Telescope were taken in July-August 2007 at 2.12 and 1.63 mu m, when the ring plane was almost edge-on (ring opening angle -0.24). These data showed, for the first time, the mu ring at infrared wavelengths. NIRCam on the James Webb Space Telescope observed Uranus in 2023-2025 at wavelengths 1.4-4.8 mu m and 60-65. Hubble Space Telescope data were obtained between 2003 and 2013 at wavelengths 0.45-0.96 mu m and from to . We confirm that the mu ring is blue and the ring red. Both rings show strong absorption bands at 3 mu m; the mu ring also shows an emission peak at 3.6 mu m. Based upon a combination of the spectral slope and absorption/emission features, the mu ring must be composed of (sub-)micron-sized icy grains. The ring is a dusty ring rich in organics (similar to 10%-15% tholins). The radial profile of both rings is triangular, with an outward extension for the ring and inward for the mu ring. Both rings are optically thin; at 1.5 mu m for the mu ring and for the ring. Based upon the composition and radial extent of the rings we suggest the mu ring to originate via micrometeoroid impacts on the icy moon Mab, and the ring via collisions between, and micrometeoroid impacts on, parent non-icy bodies embedded within this ring.

Abstract The Hubble Space Telescope collected imaging data spanning the full lifetime of Neptune's dark spot NDS‐2018, which is the sixth large, persistent dark spot seen in the planet's atmosphere. Neptune's dark spots are thought to be anticyclonic vortices, although internal flows have never been directly measured to confirm their rotation. Previous reports covered the formation and evolution of the mature NDS‐2018, while here we report that the contrast weakened over the 2021 to 2022 period, while the feature rapidly drifted equatorward from 14 deg N to 6–7 deg N planetographic latitude. The persistence of the spot so close to the equator is surprising, and represents a challenge for numerical models which find anticyclones to be disrupted within 15 deg of the equator. The changing contrast of the dark spot constrains changes in the aerosols over time, but the link between dynamical and microphysical properties of dark vortices is not known.

In 2025 July, the third-ever interstellar object, 3I/ATLAS, was discovered on its ingress into the solar system. Similar to the NASA Voyager missions sent in 1977, science probes by extraterrestrial life ("artifact technosignatures") could be sent to explore other stellar systems like our own. In this campaign, we used the SETI Institute's Allen Telescope Array to observe 3I/ATLAS from 1-9 GHz. We detected nearly 74 million narrowband hits in 7.25 hr of data using the newly developed search pipeline bliss. We then blanked hits by frequency and drift rate to mitigate radio frequency interference in our dataset, narrowing the dataset down to similar to 2 million hits. These hits were further filtered by the localization code NBeamAnalysis, and the remaining 211 hits were visually inspected in the time-frequency domain. We did not find any signals worthy of additional follow-up. Accounting for the Doppler drift correction and given the nondetection, we are able to set an effective isotropic radiated power upper limit of 10-110 W on radio technosignatures from 3I/ATLAS across the frequency and drift rate ranges covered by our survey.

Among the giant planets of the Solar System, Uranus's exceptionally low temperatures yield the weakest thermal radiance, hampering measurements of its infrared spectrum. Consequently, its thermal and compositional structures have remained poorly characterised, limiting our understanding of how atmospheric temperatures, circulation, and photochemistry respond to the planet's anomalously weak internal heat flux and the seasonal variations in insolation driven by its high axial tilt. Leveraging the exceptional sensitivity of JWST's MIRI and NIRSpec instruments, we present the first spatially resolved measurements of Uranus's spectrum spanning the near- and mid-infrared (1.66--28.70~$\mu$m), revealing how temperatures, composition, and clouds vary across the planet's northern hemisphere. Together, these observations provide the most comprehensive view of Uranus's middle atmosphere to date and offer new insights into its unique structure.

The structure of Io's atmosphere is controlled by competing processes, from volcanic outgassing and sublimation to radiative cooling and plasma heating. Yet the lack of an observationally derived temperature profile has left this balance unconstrained. We used four epochs of Atacama Large Millimeter/submillimeter Array Band 7 (275-373 GHz) and Band 8 (385-500 GHz) SO2 spectroscopy to retrieve Io's vertical atmospheric temperature profiles. To mitigate long-standing degeneracies common in atmospheric retrievals, we performed a simultaneous multiline analysis combined with line-of-sight (LOS) disk-resolved Doppler velocity maps and a forward model that included a subbeam velocity dispersion term. This modeling approach enabled the separation of thermal and dynamical line-shape contributions. On the leading hemisphere, we retrieved a cold, quasi-isothermal lower atmosphere (similar to 124-137 K up to similar to 0.5 nbar), followed by a thermospheric rise reaching hundreds of kelvins by similar to 10-2 nbar. On the trailing hemisphere, our fits yielded qualitatively similar profiles but consistently retrieved lower SO2 column densities. The lower column densities confined line formation to the first few kilometers, making the trailing hemisphere spectra statistically consistent with an isothermal atmosphere. Across datasets, we retrieved fractional gas coverages of similar to 35%-50% and subbeam velocity dispersions of similar to 25-85 m s-1, encoding LOS velocity dispersion within a beam element in excess of the disk-resolved Doppler velocity map. Together, these retrievals deliver the first vertically resolved temperature profiles of Io's atmosphere, reveal robust vertical structure on the dayside leading hemisphere, and offer new constraints on Io's thermal energy balance.

The Jupiter and Icy Moons Explorer (JUICE) mission of the European Space Agency (ESA) will investigate the Jovian system with multiple instruments over several years, beginning in early 2031. This paper describes the historical context and state of knowledge, as well as JUICE’s scientific goals and measurement techniques of the satellites that will not be encountered in close flybys. These include the large volcanically active moon Io, the four small inner moons Metis, Adrastea, Amalthea, and Thebe, and the numerous small Irregular (outer) moons. JUICE will provide multiple opportunities to observe Io from relatively remote distances of hundreds of thousands of kilometers. These observations will enable monitoring of Io’s surface for changes, and for the study of its neutral clouds and plasma torus. Io observations will be performed with the four optical remote sensing instruments and with the Particle Environment Package. For the small inner moons it is planned to obtain complete geographic longitude (scales up to 8 km/px), solar-phase and multi-color coverage, oblique polar views, and UV to near-IR spectra. Astrometric measurements will also be performed. The Irregular moons will mostly appear unresolved to the JUICE instruments. Nonetheless, long-duration disk-integrated lightcurves will be acquired to derive rotation periods, object dimensions, pole-axis orientations, and colors for most objects for the first time. From these data, convex-shape models will be generated and phase curves determined. Furthermore, the precision of the orbital elements will be improved via accurate astrometry. UV and near-IR measurements will be attempted for the largest of these objects.

Titan is an object of fascination for scientists researching the solar system, as a ‘terrestrial-like’ world with active meteorology and fluvial and lacustrine formations based on methane chemistry and condensation. The Cassini-Huygens mission explored Titan extensively from 2004 to 2017, but since that time further observation of its slow seasonal cycle has been possible only via telescopes positioned on or close to the Earth. Titan’s unique characteristics led to a concerted post-Cassini observational campaign, with many of the most powerful telescopes available to astronomy. In this work we report on observations from 2022 & 2023 with three instruments on the James Webb Space Telescope (JWST), NIRCam, NIRSpec and MIRI, also in coordination with imaging from Keck II. In November 2022 and July 2023, Titan was the subject of multi-spectral filter imaging with JWST NIRCam and Keck II NIRC2, revealing tropospheric clouds at mid-northern latitudes, in line with climate modeling predictions for this season (late northern summer). In filters sensitive to the upper troposphere, we observed clouds growing and apparently ascending in altitude during a Titan day. JWST NIRSpec spectroscopy yielded for the first time a high resolution (R=2700) spectrum of Titan across the entire near-infrared (1-5 microns) unobscured by telluric absorption. This, among other things, enabled measuring the detailed structure of the CO 4.7 micron non-LTE emission, including the fundamental, the first two overtone bands and two isotopic bands. It is also the first time that CO2 emission has been resolved in the NIR and the first time it has been seen on Titan’s dayside. Finally, very sensitive spectroscopy with JWST MIRI in the mid infrared (5-28 microns) confirmed the many stratospheric gases seen by Cassini CIRS, but also added a new detection of methyl (CH3) in the middle atmosphere, a product of methane photochemistry that was expected but not previously seen. We modeled parts of the spectra to find a global mean temperature profile and profiles of minor gases. Soon we hope to extract yet more results from the NIRSpec and MIRI spectra as our understanding of the calibration and modeling progresses. In this presentation we summarize our results to date and describe planned future observations of Titan with JWST and Keck cycles.

Towering storms, swirling clouds, and vortices are the cloud top manifestation of complex weather systems shaping the atmosphere of Jupiter. We use observations from Juno’s MicroWave Radiometer (MWR), the Karl G. Jansky Very Large Array, and the Hubble Space Telescope to probe for the first time the depth and impact of weather on Jupiter. We use ammonia, the main source of opacity at radio wavelengths on Jupiter, as the tracer for the weather by fitting ammonia anomalies to the MWR brightness temperature variations. We show that most of the weather—defined here as longitudinal deviations in ammonia concentration from the zonal mean—is concentrated in regions near cloud formation. Both the South Equatorial Belt and the Equatorial Zone have surprisingly shallow weather systems ( P < 2 bars), and even in the North Equatorial Belt most of the ammonia variations are above the water condensation level ( P ∼ 6 bars). This confirms that the water condensation layer plays a crucial role in controlling the dynamics and the weather on Jupiter. Three features, however, extend below the water condensation layer: a vortex in the northern hemisphere reaching down to 30 bars, an ammonia plume down to 20–30 bars, and the signature of ammonia fallout down to 20 bars. This work confirms that an interplay of large-scale processes (vortices, plumes) and small-scale processes (storms) is responsible for shaping the global atmospheric makeup of Jupiter.

High spatial resolution images of the volcanic moon Io at visible and near-infrared wavelengths were obtained by the SHARK-VIS and SHARK-NIR instruments on the Large Binocular Telescope on UT 2025 February 18 and 23. Large-scale changes on Io’s surface are identified in these data and provide vital context for infrared observations from other telescopes and spacecraft. SHARK-VIS imaged part of the plume deposit from a large eruption close to Io’s south pole at Illyrikon that was first observed by NASA’s Juno spacecraft in 2024 December, detecting significant deposit modification. Examples of other significant surface changes detected include at Seth, identifying a new pyroclastic deposit in addition to the new lava flows previously detected in Juno infrared observations; at Amirani, confirming that volcanic activity was now confined to the southern half of the Galileo-epoch lava flow field; new red sulphur-rich deposits at Mixcoatl; and changes in the plume deposits around Prometheus. Plume deposits at Prometheus and at other volcanoes show evidence of complex interplay between different plumes issuing from the same volcano. The combination of SHARK-VIS and Juno JunoCam data moves closer to near-global, near-contemporaneous, visible-wavelength coverage of Io. SHARK-VIS lives up to its promise of a new era of planetary imaging at visible wavelengths and filling the temporal coverage gap between Juno and the arrival of the Europa Clipper and JUICE spacecraft in the Jovian system in 2030 and 2031, respectively.

Saturn's moon Titan undergoes a long annual cycle of 29.45 Earth years. Titan's northern winter and spring were investigated in detail by the Cassini-Huygens spacecraft (2004-2017), but the northern summer season remains sparsely studied. Here we present new observations from the James Webb Space Telescope (JWST) and Keck II telescope made in 2022 and 2023 during Titan's late northern summer. Using JWST's mid-infrared instrument, we spectroscopically detected the methyl radical, the primary product of methane break-up and key to the formation of ethane and heavier molecules. Using the near-infrared spectrograph onboard JWST, we detected several non-local thermodynamic equilibrium CO and CO2 emission bands, which allowed us to measure these species over a wide altitude range. Lastly, using the near-infrared camera onboard JWST and Keck II, we imaged northern hemisphere tropospheric clouds evolving in altitude, which provided new insights and constraints on seasonal convection patterns. These observations pave the way for new observations and modelling of Titan's climate and meteorology as it progresses through the northern fall equinox, when its atmosphere is expected to show notable seasonal changes.

We present spatially resolved measurements of SO2 and NaCl winds on Io at several unique points in its orbit: before and after eclipse and at maximum eastern and western elongation. The derived wind fields represent a unique case of meteorology in a rarified, volcanic atmosphere. Through the use of Doppler shift measurements in emission spectra obtained with the Atacama Large Millimeter/submillimeter Array between similar to 346 and 430 GHz (similar to 0.70-0.87 mm), line-of-sight winds up to similar to-100 m s(-1) in the approaching direction and >250 m s(-1) in the receding direction were derived for SO2 at altitudes of similar to 10-50 km, while NaCl winds consistently reached similar to vertical bar 150-200 vertical bar m s(-1) in localized regions up to similar to 30 km above the surface. The wind distributions measured at maximum east and west Jovian elongations and on the sub-Jovian hemisphere pre- and posteclipse were found to be significantly different and complex, corroborating the results of simulations that include surface temperature and frost distribution, volcanic activity, and interactions with the Jovian magnetosphere. Further, the wind speeds of SO2 and NaCl are often inconsistent in direction and magnitude, indicating that the processes that drive the winds for the two molecular species are different and potentially uncoupled; while the SO2 wind field can be explained through a combination of sublimation-driven winds, plasma torus interactions, and plume activity, the NaCl winds appear to be primarily driven by the plasma torus.

While astronomical twilight closes the observing window for optical astronomers, the infrared sky remains dark even through sunrise, allowing IR astronomers to observe through twilight. The Slicer Combined with an Array of Lenslets for Exoplanet Spectroscopy (SCALES) instrument is a 2-5 micron coronagraphic integral field spectrograph scheduled to arrive at Keck in early 2026. SCALES has the potential to execute exciting science and support the astronomical community and upcoming NASA missions through a dedicated cadenced twilight observing program. We estimate that the current twilight observing program on Keck conducts 18+-1 hours per year of science observations; a facilitized twilight observing program that is prioritized by the observatory could yield 151+-2 hours of science time per year. This work presents the scientific motivation and high-level feasibility of two primary SCALES twilight science cases, monitoring of Solar System objects and a high-contrast imaging search for exoplanets around bright nearby stars, taking lessons from the existing NIRC2 and OSIRIS Twilight Zone program and considering increases in program scope. We also consider technical and operational challenges to overcome before the SCALES instrument begins its twilight observing program.

We study the spatial and temporal variability in Jupiter's atmosphere by comparing longitude-resolved brightness temperature maps from the Very Large Array radio observatory and NASA's Juno spacecraft Microwave Radiometer taken between 2013 and 2018. Spatial variations in brightness temperature, as observed at radio wavelengths, indicate dynamics in the atmosphere as they trace spatial fluctuations in radio-absorbing trace gases or physical temperature. We use four distinct frequency bands, probing the atmosphere from the water cloud region at the lowest frequency to the pressures above the ammonia cloud deck at the highest frequency. We visualize the brightness temperature anomalies and trace dynamics by analyzing the shapes of brightness temperature anomaly distributions as a function of frequency in Jupiter's North Equatorial Belt (NEB), Equatorial Zone (EZ), and South Equatorial Belt (SEB). The NEB has the greatest brightness temperature variability at all frequencies, indicating that more extreme processes are occurring there than in the SEB and EZ. In general, we find that the atmosphere at 5 and 22 GHz has the least variability of the frequencies considered, while observations at 10 and 15 GHz have the greatest variability. When comparing the size of the features corresponding to the anomalies, we find evidence for small-scale events primarily at the depths probed by the 10 and 15 GHz observations. In contrast, we find larger-scale structures deeper (5 GHz) and higher (22 GHz) in the atmosphere.

The Orbiting Configurable Artificial Star (ORCAS) mission in collaboration with the W. M. Keck Observatory has designed, assembled, built, and delivered, within 180 days, ORCAS Keck Instrument Demonstrator (ORKID) (ORCAS Keck Instrument Demonstrator), an early visible-wavelength performance demonstration with the Keck II Adaptive Optics (AO) system. The optical performance of ORKID meets the technical requirements derived from the scientific goals of having a Nyquist-sampled point spread function at 650 nm. This is achieved by diffraction-limited as-built performance with a root mean square internal wavefront error below 50 nm, which is key for the advancement of the ORCAS mission. ORKID has acquired, with a closed AO loop, no frame selection, while shifting and adding, the sharpest-ever on-sky image captured at Keck II. With a full width at half maximum of similar to 15 mas, this is the equivalent of a 9-m diffraction-limited telescope. By doing so, the immense potential and viability of the proposed Hybrid Observatory ORCAS mission are demonstrated. (c) 2025 Society of Photo-Optical Instrumentation Engineers (SPIE) [DOI:

Storms are emerging as key drivers in shaping hydrogen-dominated atmospheres. Trace gas condensation can suppress convection and disrupt the distribution of energy and material in hydrogen atmospheres. On Jupiter, the presence of water has been invoked to control the occurrence of large-scale storms; however, the impact of storms on the ammonia and temperature distribution is unknown. We use Juno Microwave Radiometer observations of a large-scale storm in 2017 to study the aftermath of such a storm on the atmosphere. Anomalies in the retrieved ammonia abundance and atmospheric temperature show how storms deplete and heat the upper atmosphere while simultaneously depositing material well below the layers they were triggered at. These observations, aided by simulations, show that the water and ammonia cycles are coupled and that their combined effect plays a key role in explaining the depletion of ammonia in the tropospheres of Jupiter and Saturn.

Context. The impact of the Shoemaker-Levy 9 (SL9) comet on Jupiter in 1994 opened up a new field of study focused on the exogenic species within Jupiter's atmosphere. Among these species, we find H2O, CO, and HCN. It is thought that these species coexist at the same pressure level (similar to 3 mbar in 2022) and that the interaction between some of them creates daughter molecules such as CO2. However, understanding their complex meridional distributions is still a matter of debate. Aims. We measured the meridional distribution of H2O, HCN, and CO2 to understand the chemistry and dynamics leading to these distributions. Methods. We used James Webb Space Telescope (JWST) Mid InfraRed Instrument (MIRI) medium-resolution spectroscopy observations from 17(degrees)S to 26(degrees)S, and from 45(degrees)S towards the south pole for CO2, H2O, and HCN. We used a radiative transfer code coupled with an inversion algorithm to retrieve the temperature using the CH4 v(4) band and the abundance of the species for the different latitudes. Results. We found an increase in H2O in the south polar region, while CO2 is found to be depleted, which points towards an exchange of oxygen between H2O and CO2 happening in the southern auroral region. The HCN abundance decreases towards the pole, and abundance values are similar to the ones obtained with ALMA in 2017. The depletion of HCN may be due to heterogeneous chemistry related to stratospheric polar aerosols. Conclusions. The exogenic molecules analysed seem to be influenced either by polar aerosols produced by ion-neutral chemistry (e.g. HCN) or by particle precipitation occurring in the auroral regions (e.g. H2O and CO2). These measurements provide new insights into chemical evolution at a small spatial scale, revealing previously undetected localized trends.

The impact of the Shoemaker-Levy 9 (SL9) comet on Jupiter in 1994 opened up a new field of study focused on the exogenic species within Jupiter's atmosphere. Among these species, we find H_2O, CO, and HCN. It is thought that these species coexist at the same pressure level (∼ 3 mbar in 2022) and that the interaction between some of them creates daughter molecules such as CO_2.However, understanding their complex meridional distributions is still a matter of debate. We measured the meridional distribution of H_2O, HCN, and CO_2 to understand the chemistry and dynamics leading to these distributions. We used James Webb Space Telescope (JWST) Mid InfraRed Instrument (MIRI) medium-resolution spectroscopy observations from 17^∘S to 26^∘S, and from 45^∘S towards the south pole for CO_2, H_2O, and HCN. We used a radiative transfer code coupled with an inversion algorithm to retrieve the temperature using the CH_4 ν_4 band and the abundance of the species for the different latitudes. We found an increase in H_2O in the south polar region, while CO_2 is found to be depleted, which points towards an exchange of oxygen between H_2O and CO_2 happening in the southern auroral region. The HCN abundance decreases towards the pole, and abundance values are similar to the ones obtained with ALMA in 2017. The depletion of HCN may be due to heterogeneous chemistry related to stratospheric polar aerosols. The exogenic molecules analysed seem to be influenced either by polar aerosols produced by ion-neutral chemistry (e.g. HCN) or by particle precipitation occurring in the auroral regions (e.g. H_2O and CO_2). These measurements provide new insights into chemical evolution at a small spatial scale, revealing previously undetected localized trends.

We present center-surround application to James Webb Space Telescope (JWST), Near Infrared Imager and Slitless Spectrograph (NIRISS) observations of Io, Jupiter's innermost moon. This project is part of the JWST Early Release Science pro- gram ERS1373 (Co-PI's Imke de Pater, Thierry Fouchet) on the Jovian system. Io is the most geologically active body in our solar system; however, the locations of tidal heating in the interior and temperature of Io's magma leading to the volcanic eruptions are not well constrained (Keszthelyi et al. 2016). NIRISS's Aperture Masking Interferometry (AMI) mode that utilizes a 7-hole non-redundant mask (NRM) in its pupil plane provides high-resolution imaging with moderate contrast and better astrometric accuracy over a wide field of view than conventional imaging. We present interferometric observations of Io from ERS1373 using NRM and filter F430M that is well matched to the emission from Io's 500 K to ~1500 K lava flows. Convolution of Io images with the center-surround kernel emphasizes fine structure on Io's disk. This convolved image is used as a 'prior' to reconstruct images from Io's interferometric data, thus helping to provide new measurements of the global distribution of vulcanism on Io.

We present thermal observations of Callisto's leading and trailing hemispheres obtained using the Atacama Large Millimeter/submillimeter Array (ALMA) at 0.87 mm (343 GHz), 1.3 mm (233 GHz), and 3 mm (97 GHz). The angular resolution achieved for these observations ranged from 0.09-0.24 arcseconds, corresponding to 420-1100 km at Callisto. Global surface properties were derived from the observations using a thermophysical model (de Kleer et al. 2021) constrained by spacecraft data. We find that Callisto's millimeter emissivities are high, with representative values of 0.85-0.97, compared to 0.75-0.85 for Europa and Ganymede at these wavelengths. It is clear that models parameterized by a single thermal inertia are not sufficient to model Callisto's thermal emission, and clearly deviate from the temperature distributions in the data in systematic ways. Rather, more complex models that adopt either two thermal inertia components or that treat electrical skin depth as a free parameter fit the data more accurately than single thermal inertia models. Residuals from the global best-fit models reveal thermal anomalies; in particular, brightness temperatures that are locally 3-5 K colder than surrounding terrain are associated with impact craters. We identify the Valhalla impact basin and a suite of large craters, including Lofn, as key cold anomalies ( 3-5 K) and geologic features of interest in these data. These data provide context for Callisto JWST results (Cartwright et al. 2024) as well as the other ALMA Galilean moon observations (de Kleer et al. 2021, Trumbo et al. 2017, 2018, Thelen et al. 2024), and may be useful ground-based context for upcoming Galilean satellite missions (JUICE, Europa Clipper).