JWST Reveals the Kuiper Belt-like Compositions of the Uranian Rings and Small Moons
Abstract
We present the JWST NIRSpec 1--5 micron spectra of the Uranian rings and four ringmoons: Puck, Perdita, Portia, and Juliet. We find that the compositions of the rings and moons strongly resemble water-type Kuiper belt objects, showing deep 3.0 micron O--H and water ice features as well as the CO2 band at 4.27 micron. The volatiles show a radial trend of decreasing volatile abundance at closer radial distance to the planet, consistent with recent estimates of the densities of the innermost moons. Given the observed compositional signatures, we suggest two ways to reconcile the history of the small inner moons with that of the regular ones. The first is that the Uranus-tilting collision produced a disk from an impactor formed out of material similar to that which comprises water-rich Kuiper belt objects, and the ringmoons are small undifferentiated remnants of that process. Alternatively, the rings and ringmoons postdate the formation of the regular moons, and formed from the later tidal disruption of a several hundred kilometer sized undifferentiated water-type Kuiper belt object.
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BibTeX
@misc{belyakov2026jwst,
title = {{JWST Reveals the Kuiper Belt-like Compositions of the Uranian Rings and Small Moons}},
author = {Matthew Belyakov and M. Ryleigh Davis and Zachariah Milby and Ian Wong and Michael E. Brown},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.31923},
eprint = {2609.31923},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.31923},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - JWST Reveals the Kuiper Belt-like Compositions of the Uranian Rings and Small Moons
AU - Matthew Belyakov
AU - M. Ryleigh Davis
AU - Zachariah Milby
AU - Ian Wong
AU - Michael E. Brown
PY - 2026
DA - 2026/09/25
PB - arXiv
DO - 10.48550/arxiv.2609.31923
UR - https://arxiv.org/abs/2609.31923
AB - We present the JWST NIRSpec 1--5 micron spectra of the Uranian rings and four ringmoons: Puck, Perdita, Portia, and Juliet. We find that the compositions of the rings and moons strongly resemble water-type Kuiper belt objects, showing deep 3.0 micron O--H and water ice features as well as the CO_2 band at 4.27 micron. The volatiles show a radial trend of decreasing volatile abundance at closer radial distance to the planet, consistent with recent estimates of the densities of the innermost moons. Given the observed compositional signatures, we suggest two ways to reconcile the history of the small inner moons with that of the regular ones. The first is that the Uranus-tilting collision produced a disk from an impactor formed out of material similar to that which comprises water-rich Kuiper belt objects, and the ringmoons are small undifferentiated remnants of that process. Alternatively, the rings and ringmoons postdate the formation of the regular moons, and formed from the later tidal disruption of a several hundred kilometer sized undifferentiated water-type Kuiper belt object.
ER -