1,2,6,7,8- 1Departments of Astronomy and of Earth and Planetary Science, Berkeley, University of California , CA 94720, USA (imke@berkeley.edu)
- 2SETI Institute, Mountain View, CA 94043, USA
- 3Department of Physics, University of Idaho, Moscow, ID 83843, USA
- 4AURA, Washington, DC 20004, USA
- 5Universidad Adolfo Ibáñez, Santiago, Chile 8170121
- 6chool of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK
- 7Southwest Research Institute, Boulder, CO 80302, USA
- 8LIRA, CNRS UMR-8254, Observatoire de Paris, Meudon, FR
The outermost rings in the uranian system, the µ and the v rings, were discovered on HST images taken in 2003-2005 (Showalter & Lissauer, 2006). The color of the rings was established soon thereafter from Keck images taken in 2005 (de Pater et al., 2006). While the v ring had the typical red color as expected for dusty rings, the µ ring seemed to be as blue as Saturn’s E ring. The spectra of these rings were based on two datapoints: one in the visible and one in the infrared (2.12 µm), while the infrared data point of the µ ring was only a 3-sigma upper limit.
In July-August 2007 we used NIRC2 on the Keck telescope in Hawaii at 2.12 and 1.63 µm in an attempt to detect the µ ring. At this time the ring plane was almost edge-on (B=0.62-0.24 deg.), and these data show the first detection of the µ ring at infrared wavelengths.
More recently, the Uranian rings were imaged by JWST in 2023 as part of the Cycle 1 Outreach Campaign (#2739), which illustrated JWST’s remarkable sensitivity to the faint dust rings. In 2024, JWST GTO program #2768 included the first Uranus rings science observations (in addition to other planet-related goals). We also include deep exposures from 2025, taken for JWST GO #6379 which was specifically focused on the uranian rings and inner moons to characterize the uranian system in the immediate environment of the planet. All JWST observations were obtained with NIRCam, at wavelengths between 1.4 and 4.8 µm and ring opening angles B = 56-65 deg. These data show both the µ and ν rings at several wavelengths.
We complement these infrared datasets with HST data at visible wavelengths, obtained between 2003 and 2013, at several ring opening angles between roughly minus 20 and plus 20 deg.
We used the images to construct spectra of both rings to validate their color. We confirm that the v ring is indeed red, and the µ ring blue. Both rings show strong absorption bands at 3 µm, indicative of water ice and/or OH-rich material.
As previously noted, the µ ring peaks in brightness very close to the orbit of Mab, which probably serves as a source body for the fine (icy) dust grains, although the mechanism at work remains obscure. The radial profile of both rings is triangular at all wavelengths, similar to that observed by HST and Voyager at visible wavelengths (Showalter & Lissauer, 2006). However, the µ ring appears to be radially wider at shorter wavelengths, suggesting that smaller dust grains are distributed more widely than are the larger grains that dominate at IR wavelengths. This is consistent with models that suggest that non-gravitational forces play an important role in this ring. We further noticed a steep decline in the intensity of the µ ring in HST data from 2003 through 2006.
References:
de Pater, I., Hammel, H.B., Gibbard, S., Showalter, M.R., 2006. Science 312, 92.
Showalter, M.R., Lissauer, J.J., 2006. Science 311, 973.
How to cite: de Pater, I., Showakter, M., Hedman, M., Hammel, H., Roman, M., Fletcher, L., El Moutamid, M., Tiscareno, M., and Souami, D.: Characterization of the outer Uranian rings in the visual and near-IR using Keck, JWST, and HST observations , EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–12 Sep 2025, EPSC-DPS2025-959, https://doi.org/10.5194/epsc-dps2025-959, 2025.
