S/2025 U 1

S/2025 U 1 is a small moon of Uranus, with an estimated diameter between 8 and 10 kilometres (5 and 6 miles).^[3] It was the 29th moon identified in the Uranus system. The discovery was announced in August 2025 by a team of astronomers led by Maryame El Moutamid,^[a] who found the moon in James Webb Space Telescope NIRCam images taken on 2 February 2025.^[1][c]

S/2025 U 1

Discovery image of S/2025 U 1 (circled) by the James Webb Space Telescope on 2 February 2025
Discovery[1]
Discovered by	Maryame El Moutamid et al.[a]
Discovery site	James Webb Space Telescope
Discovery date	2 February 2025 (date of discovery images)[1]
Orbital characteristics[2]
Epoch 1 January 2025 TDB
Semi-major axis	57844 km
Eccentricity	0.039
Orbital period (sidereal)	0.4021 d (9.65 h)
Mean anomaly	275.6°
Inclination	4.0° (wrt local Laplace plane[b])
Longitude of ascending node	70.8°
Argument of perihelion	313.9°
Satellite of	Uranus
Physical characteristics
Mean diameter	8–10 km (5–6 mi)[1][3]
Albedo	0.05–0.10 (assumed)[1]
Apparent magnitude	25.5 (H-band)

The moon orbits about 57,844 km (35,943 mi) from the center of Uranus (between the orbits of Ophelia and Bianca) with an orbital period of 9.6 hours (0.402 days).^[2] Like the other inner moons of Uranus, it follows a nearly circular orbit along Uranus's equatorial plane.^[1] Due to its small size, it appears extremely faint with a near-infrared (H-band) apparent magnitude of 25.5—too faint to be seen by the Hubble Space Telescope and the Voyager 2 spacecraft.^[1]

Name

S/2025 U 1 is the provisional designation of this unnamed moon.^[4] By convention, the moons of Uranus are named after characters from the plays of William Shakespeare and Alexander Pope.^[3] A proper name will be given once it is approved by the International Astronomical Union.^[3][4] Co-discoverer Mark R. Showalter has stated in a 2025 New Scientist article that "there have been discussions [of a name for S/2025 U 1] but no shortlist as yet."^[4]

Orbit

JWST timelapse of S/2025 U 1 (circled) orbiting Uranus, along with Miranda (upper left) and the rest of Uranus's inner moons

S/2025 U 1 is the 14th known member of Uranus's inner moons, which are small moons that orbit interior to the planet's five largest moons (Miranda, Ariel, Umbriel, Titania, and Oberon).^[3] S/2025 U 1 follows a nearly circular orbit around Uranus's equatorial plane, at a distance of 57,844 km (35,943 mi) from the planet's center with an orbital period of 9.6 hours (0.402 days).^[2] S/2025 U 1 is located outside the edge of Uranus's inner ring system, between the orbits of Ophelia and Bianca.^[4] The nearly circular orbit of S/2025 U 1 suggests that it formed near its current location, according to El Moutamid.^[3]

Notes

1. The full team of researchers involved in the discovery of this moon includes: Maryame El Moutamid, Matthew M. Hedman, Mark R. Showalter, Matthew Tiscareno, Imke de Pater, Jack J. Lissauer, and Damya Souami.^[1]
2. The local Laplace plane is the plane containing the satellite's nodal orbital precession. For regular moons of Uranus, their Laplace planes are usually closely aligned with the plane of Uranus's equator.^[2]
3. The NIRCam discovery observations consisted of ten consecutive near-infrared images, each with 40-minute-long exposure times.^[3]