Uranus adds a new satellite to its catalog after a detection made with the Space Telescope. James WebbThe discovery, led by a team from the Southwest Research Institute (SwRI), reveals an extremely faint moon that had gone unnoticed in previous surveys.
The object, provisionally designated S/2025 U1, has an estimated diameter of about 10 kilometers and is integrated into the planet's dense interior. With its incorporation, the number of known moons of Uranus rises to 29.
How detection was achieved with the James Webb
The new moon was identified in a series of ten 40-minute presentations captured by Webb's NIRCam near-infrared camera during an observing session on February 2th 2025. In that data set, a weak spot appeared with motion consistent with that of Uranus's satellites, Uranus discoveries by JWST.
The person in charge of the analysis, Maryame El Moutamid (SwRI), emphasizes that this is a small but significant moon: its detection confirms the leap in Webb's sensitivity compared to previous missions and telescopes. The combination of high resolution and infrared sensitivity has been key to distinguishing such a faint object in a complex environment.
Webb allowed the planet's brightness, the glow of its rings, and the transiting moons to be integrated into a composite image. In that context, S/2025 U1 It stood out for its movement between shots, which confirmed its orbital nature in the face of possible artifacts or background sources.
This work is part of the program of General Observer Webb, which is open to teams from around the world. Thanks to this availability, tracking targets in the outer solar system is producing results that tangibly expand existing catalogs.
Where it is and what role it plays in the Uranus system
Calculations place the new moon at about 56.000 kilometers from the planet's center, within the equatorial plane. Its nearly circular trajectory suggests an origin close to its current position, rather than a subsequent gravitational capture.
S/2025 U1 moves between the orbits of Ofelia and Bianca, within the region where the smallest and darkest satellites are concentrated. It thus becomes the fourteenth inner group moon, an area that interacts closely with the planet's rings.
For Matthew Tiscareno (SETI Institute), the network of rings and minor satellites of Uranus points to a chaotic dynamics where the boundaries between the two systems become blurred. This complexity, and the even smaller size and weaker brightness of S/2025 U1, support the idea that they could remain more moons to discover in the zone.
Although the Webb has allowed us to see an object that Voyager 2 did not detect during its 1986 flyby, the result is consistent with the estimated size and albedo. A moon around 10 kilometers across, with reflectivity similar to other internal ones, would have been too faint for earlier instruments.
The cluster of small moons helps to confine and sculpt the most subtle rings, a function that makes these bodies key pieces to understand the stability and evolution of the Uranus system in the medium and long term.
Provisional name and next steps
The provisional designation S/2025 U1 will remain until the International Astronomical Union (IAU) validates the discovery and approves a definitive name, as per standard procedure.
If tradition is followed, the chosen name will come from characters from Shakespeare or Alexander Pope, as is the case with the rest of the Uranian moons. Formal confirmation and naming will come after further observations that refine the orbit and brightness of the object.
The team notes that Webb's sensitivity opens the door to identifying more faint satellites in Uranus's vicinity. That prospect, along with future missions dedicated to the planet, promises to improve the picture of a system where rings and inner moons are closely coupled.
With this detection, the inventory of known satellites of the planet reaches 29 months, reinforcing the idea that, even in our astronomical neighborhood, there were still details to be resolved that only state-of-the-art instrumentation could reveal.
The identification of S/2025 U1 With the James Webb it fits into a line of advances that are refining the photography of the Uranian system: a tiny moon, 56.000 km from the center of the planet, which becomes part of the internal group and which, pending approval from the IAU, demonstrates how new techniques continue to bring to light key pieces to understand the architecture of Uranus.