The James Webb Space Telescope (JWST) has identified a previously unknown moon orbiting the ice giant Uranus, increasing the planet's known satellite count from 28 to 29. The discovery was announced on August 19, 2025.
The newly discovered celestial body, provisionally designated S/2025 U1, was first observed on February 2, 2025, through analysis of data from Webb's Near-Infrared Camera (NIRCam). S/2025 U1 is a small moon, estimated to be approximately six miles (10 kilometers) in diameter. Its diminutive size and faintness are believed to be the reasons it evaded detection by earlier missions, including the Voyager 2 flyby in January 1986.
S/2025 U1's orbit is notably circular, suggesting its formation likely occurred in its current vicinity. It resides approximately 35,000 miles (56,000 kilometers) from Uranus's center, situated between the orbital paths of the moons Ophelia and Bianca. The discovery highlights the JWST's advanced capabilities in discerning faint and small celestial objects.
Uranus's moons are famously named after characters from the literary works of William Shakespeare and Alexander Pope. S/2025 U1 awaits official naming approval from the International Astronomical Union (IAU). This discovery contributes to a more profound understanding of Uranus's complex moon and ring architecture, hinting at a dynamic past.
Scientists, including Maryame El Moutamid from the Southwest Research Institute, who led the discovery team, have noted that Uranus possesses an unusual number of small inner moons, suggesting a complex history that blurs the lines between its ring system and its moons. Matthew Tiscareno of the SETI Institute further commented that the discovery implies that more complexity within Uranus's satellite system remains to be uncovered.
The JWST's advanced sensitivity continues to build upon the legacy of past missions like Voyager 2, which provided humanity's first close-up view of Uranus. While Voyager 2 discovered 10 of Uranus's moons, the JWST's capabilities are pushing the frontiers of our knowledge, revealing details previously beyond reach. The ongoing exploration of Uranus's system promises to shed light on the formation and evolution of planetary systems in the outer reaches of our solar system.