Characterization of the Outer Uranian Rings in the Visual and Near‐IR Using Keck, JWST, and HST Observations
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 B = 0.62-0.24°). 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 B ∼ 60-65°. Hubble Space Telescope data were obtained between 2003 and 2013 at wavelengths 0.45-0.96 μm and B from -17°to +25°. We confirm that the μ ring is blue and the ν 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 ν 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 ν ring and inward for the μ ring. Both rings are optically thin; at 1.5 μm τ 0 ≈ 10 -5 for the μ ring and 3 × 10 -5 for the ν 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 ν ring via collisions between, and micrometeoroid impacts on, parent non-icy bodies embedded within this ring.
Plain Language SummaryWe present observations of the Uranian outer ring system, the μ and ν rings, at visible and near-infrared wavelengths. The observations were obtained with the Hubble Space Telescope, Keck and the James Webb Space Telescope at different ring opening angles, from almost "open" (∼ 60°) to essentially edge-on (∼ 0.24°). We confirm that the μ ring is blue and the ν ring red. A blue color is indicative of Rayleigh scattering, that is, the presence of (sub-)micron-sized particles, while a red color is the telltale sign of a dusty ring. Both rings show a strong absorption band near 3 μm, but the spectra look different longwards of this absorption feature. The μ ring spectrum is very similar to that of water-ice, while the ν ring spectrum resembles a rocky composition mixed in with ∼10%-15% organic material, analogous to tholins. Both rings are optically thin. We suggest that the μ ring has been formed through micrometeoroid impacts on the icy moon Mab, liberating the tiny icy grains that make up this ring. The ν ring, like typical dusty rings, is sourced from collisions between, and micrometeoroid impacts on, larger but as yet unseen parent bodies orbiting within this ring. These bodies must be composed in part of organic materials.
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BibTeX
@article{pater2026characterization,
title = {{Characterization of the Outer Uranian Rings in the Visual and Near‐IR Using Keck, JWST, and HST Observations}},
author = {Imke de Pater and Mark R Showalter and Matt M Hedman and Heidi B Hammel and Mike Roman and Leigh N Fletcher and Maryame El Moutamid and Damya Souami},
journal = {Journal of Geophysical Research. Planets},
year = {2026},
month = oct,
doi = {10.1029/2025je009404},
url = {https://hal-obspm.ccsd.cnrs.fr/obspm-05805972v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Characterization of the Outer Uranian Rings in the Visual and Near‐IR Using Keck, JWST, and HST Observations
AU - Imke de Pater
AU - Mark R Showalter
AU - Matt M Hedman
AU - Heidi B Hammel
AU - Mike Roman
AU - Leigh N Fletcher
AU - Maryame El Moutamid
AU - Damya Souami
PY - 2026
DA - 2026/10/19
JO - Journal of Geophysical Research. Planets
DO - 10.1029/2025je009404
UR - https://hal-obspm.ccsd.cnrs.fr/obspm-05805972v1
AB - 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 B = 0.62-0.24°). 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 B ∼ 60-65°. Hubble Space Telescope data were obtained between 2003 and 2013 at wavelengths 0.45-0.96 μm and B from -17°to +25°. We confirm that the μ ring is blue and the ν 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 ν 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 ν ring and inward for the μ ring. Both rings are optically thin; at 1.5 μm τ 0 ≈ 10 -5 for the μ ring and 3 × 10 -5 for the ν 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 ν ring via collisions between, and micrometeoroid impacts on, parent non-icy bodies embedded within this ring. Plain Language SummaryWe present observations of the Uranian outer ring system, the μ and ν rings, at visible and near-infrared wavelengths. The observations were obtained with the Hubble Space Telescope, Keck and the James Webb Space Telescope at different ring opening angles, from almost "open" (∼ 60°) to essentially edge-on (∼ 0.24°). We confirm that the μ ring is blue and the ν ring red. A blue color is indicative of Rayleigh scattering, that is, the presence of (sub-)micron-sized particles, while a red color is the telltale sign of a dusty ring. Both rings show a strong absorption band near 3 μm, but the spectra look different longwards of this absorption feature. The μ ring spectrum is very similar to that of water-ice, while the ν ring spectrum resembles a rocky composition mixed in with ∼10%-15% organic material, analogous to tholins. Both rings are optically thin. We suggest that the μ ring has been formed through micrometeoroid impacts on the icy moon Mab, liberating the tiny icy grains that make up this ring. The ν ring, like typical dusty rings, is sourced from collisions between, and micrometeoroid impacts on, larger but as yet unseen parent bodies orbiting within this ring. These bodies must be composed in part of organic materials.
SN - 2169-9097
SN - 2169-9100
ER -