Characterization of the Outer Uranian Rings in the Visual and Near‐IR Using Keck, JWST, and HST Observations
Year: 2026
Type: article
Abstract: 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 μm, when the ring plane was almost edge‐on (ring opening angle –0.24). These data showed, for the first time, the μ ring at infrared wavelengths. NIRCam on the James Webb Space Telescope observed Uranus in 2023–2025 at wavelengths 1.4–4.8 μm and 60–65. Hubble Space Telescope data were obtained between 2003 and 2013 at wavelengths 0.45–0.96 μm and from to . We confirm that the μ ring is blue and the ring red. Both rings show strong absorption bands at 3 μm; the μ ring also shows an emission peak at 3.6 μm. Based upon a combination of the spectral slope and absorption/emission features, the μ ring must be composed of (sub‐)micron‐sized icy grains. The ring is a dusty ring rich in organics (∼10%–15% tholins). The radial profile of both rings is triangular, with an outward extension for the ring and inward for the μ ring. Both rings are optically thin; at 1.5 μm for the μ ring and for the ring. Based upon the composition and radial extent of the rings we suggest the μ 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.
DOI: 10.1029/2025je009404
Institutions: University of California, Berkeley, Search for Extraterrestrial Intelligence, University of Idaho, Adolfo Ibáñez University, University of Leicester, Southwest Research Institute, Centre National de la Recherche Scientifique, Observatoire de Paris, LIRA - Laboratoire d'instrumentation et de recherche en astrophysique
Language: English
Topic: Astro and Planetary Science
Subfield: Space and Planetary Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $4,070
Awards: MOTIVATION: ALTHOUGH URANUS DID NOT SHOW MUCH EVIDENCE OF CLOUDS DURING THE VOYAGER ERA (1986) WHEN THE PLANET APPROACHED ITS 2007 EQUINOX NUMEROUS CLOUD FEATURES POPPED UP INDICATIVE OF A DRAMATIC INCREASE IN DYNAMIC ACTIVITY. EVEN MORE SURPRISING WAS THE EXTREME CLOUD ACTIVITY OBSERVED IN 2014 SEVEN YEARS AFTER EQUINOX. THERE ARE A NUMBER OF STRIKING CLOUD FEATURES: I) LARGE CLOUDSTHAT LOOK LIKE GROUPS OF DISCRETE CLOUD FEATURES: SUCH CLOUDS HAVE BEEN SEEN ON BOTH HEMISPHERES SOMETIMES FOR MANY YEARS BEFORE THEY DISAPPEAR. SINCE THEY EXTEND OVER A FEW DEGREES IN LATITUDE ONE WOULD EXPECT THEM TO SHEAR APART; HOWEVER THEY DONT. THEY SOMETIMES ARE ACCOMPANIED BY A DARK SPOT; THIS AND THE APPARENT COHERENCE ARE SUGGESTIVE THAT VORTICES IN THE DEEPER ATMOSPHERE MAY BE RESPONSIBLE FOR THESE CLOUDS. II) POLAR FEATURES: WHEN VOYAGER 2 ARRIVED AT URANUS IN 1986 THE SOUTH POLE WAS FACING THE SUN AND A FEATURELESS BRIGHT SOUTH POLAR HAZE WAS SEEN AT HIGH LATITUDES. WHEN THE NORTH POLAR REGION CAME INTO VIEW NUMEROUS SMALL DISCRETE CLOUD FEATURES WERE OBSERVED. IN ADDITION TO THESE CLOUDS THE CONDENSABLE GASES (CH4 NH3 H2S) APPEAR TO BE DEPLETED OVER BOTH THE NORTH AND SOUTH POLAR REGIONS OF URANUS AS INDICATED BY HST/STIS AND MICROWAVE OBSERVATIONS. ALTHOUGH THE LATTER DATA ARE SUGGESTIVE OF SUBSIDING MOTIONS OVER THE POLES THIS SEEMS IN DIRECT CONTRAST TO THE NUMEROUS CLOUD FEATURES NEAR THE NORTH POLE. OUR AIM IN THIS PROPOSAL IS TO DETERMINE THE DYNAMICS IN URANUS ATMOSPHERE BOTH ON GLOBAL (GLOBAL CIRCULATION) AND LOCAL (VORTICES STORMS) SCALES.OBJECTIVES/METHODOLOGY: WE WILL USE THE UPGRADED VLA IN ITS MOST EXTENDED ARRAY TO PRODUCE MAPS OF THE PLANET THAT ARE RESOLVED IN BOTH LATITUDE AND LONGITUDE PROVIDING RESOLUTIONS ON SCALES AS SMALL AS 1500 KM OR ~30 IN LATITUDE/LONGITUDE AT DISK CENTER. WE WILL SIMULTANEOUSLY OBSERVE WITH HST AND KECK IN THE VISIBLE-NIR TO CHARACTERIZE THE CLOUDS. THE COMBINATION ENABLES US TO COUPLE CLOUD FORMATION TO GAS DYNAMICS AND CONDENSATION. SUCH DATA ARE CRITICAL FOR UNDERSTANDING THE GLOBAL CIRCULATION PATTERN LOCALIZED STORM SYSTEMS AND TURBULENT MOTIONS IN URANUS ATMOSPHERE. ALMA OBSERVATIONS WILL BE CONDUCTED TO PROBE THE UPPER TROPOSPHERE AND LOWER STRATOSPHERE. SUCH DATA ARE CRITICAL FOR UNDERSTANDING THE GLOBAL CIRCULATION PATTERN LOCALIZED STORM SYSTEMS AND TURBULENT MOTIONS IN URANUS'S ATMOSPHERE.RELEVANCE: IN NASAS 2014 SCIENCE PLAN FOR 2013--2022 NASA'S SCIENCE VISION IS DESCRIBED AS: ASCERTAIN THE CONTENT ORIGIN AND EVOLUTION OF THE SOLAR SYSTEM AND THE POTENTIAL FOR LIFE ELSEWHERE WHICH HAS BEEN TRANSLATED INTO: TO EXPLORE AND OBSERVE THE OBJECTS IN THE SOLAR SYSTEM TO UNDERSTAND HOW THEY FORMED AND EVOLVED AND TO ADVANCE THE UNDERSTANDING OF HOW CHEMICAL AND PHYSICAL PROCESSES IN OUR SOLAR SYSTEM OPERATE INTERACT AND EVOLVE. IN THIS PROPOSAL WE INTEND TO STUDY URANUS USING GROUNDBASED OBSERVATIONS. THESE OBSERVATIONS ALONG WITH THEIR ANALYSIS CONFORM TO THE ABOVE VISION AND ARE IMPORTANT TO HELP PREPARE FOR FUTURE MISSIONS AND UNDERSTAND THE VOYAGER DATA IN TERMS OF SEASONAL CHANGES. THEY ALSO HELP UNDERSTAND EXOPLANETS AN IMPORTANT GOAL INNASAS ASTROPHYSICS DIVISION., G256731684, G58316358
OpenAlex ID: W4412120561