NIRCam view of Uranus showing the new moon S/2025 U 1 (circled). Composite processing reveals the atmosphere, rings, and faint satellites. Data: F150W2 filter, 1.0–2.4 microns. [Credit: NASA, ESA, CSA, STScI, M. El Moutamid (SwRI), M. Hedman (University of Idaho)]
S/2025 U 1 travels on a nearly circular, equatorial path about 56,250 km (34,950 miles) from Uranus’ center, between Ophelia and Bianca at the outer edge of the inner ring system. Based on its distance, the satellite completes an orbit in about 9.6 hours.
By convention, Uranian moons are named for characters from Shakespeare and Alexander Pope. Once follow-up observations and orbit solutions are finalized, the IAU will consider a formal name for S/2025 U 1.
How it was detected
The team, led by Maryame El Moutamid of Southwest Research Institute, used JWST/NIRCam to take ten 40-minute exposures spanning roughly 6 hours (Program ID 6379). The discovery sequence was taken with the F150W2 wide-band filter (about 1.0–2.4 μm) and processed as composites to manage the extreme dynamic range of Uranus, its rings, and faint moons—conditions that likely hid the object from Voyager 2 and Hubble. Assuming a typical dark albedo for inner Uranian moons, the size estimate is ~10 km; the object appears at roughly 25th magnitude in the near-IR.
Why this matters for R&D
From an R&D standpoint, the observation pushes JWST’s practical limits in a glare-dominated field. NIRCam delivered the contrast and sensitivity needed to pick out a ~10 km, likely low-albedo body close to a bright primary, a geometry directly relevant to future surveys of small moons and ring particles. On the data-reduction side, the team combined ten 40-minute exposures into high-dynamic-range composites and used point-spread-function modeling, glare suppression and artifact rejection to separate faint sources from Uranus’ rings and atmosphere. Post-processing choices of that kind can recover signals below nominal dynamic-range thresholds. On system dynamics, S/2025 U 1 becomes the 14th inner moon of Uranus, reinforcing evidence for a crowded, interacting population coupled to the rings and consistent with a stirred, collisionally evolved inner system. Additional sub-10 km satellites are likely as JWST data accumulate.
