Key Takeaways:
- A new Uranian moon, provisionally designated S/2025 U1, has been discovered using the James Webb Space Telescope (JWST).
- S/2025 U1 is estimated to be 10 kilometers in diameter and orbits Uranus between the orbits of Ophelia and Bianca.
- This discovery increases the known number of Uranian moons to 29, further highlighting the complex system of small inner moons surrounding the planet.
- The discovery underscores the enhanced capabilities of JWST in detecting smaller celestial bodies compared to previous missions, such as Voyager 2.
Astronomers have discovered a new, tiny moon orbiting Uranus, bringing the ice giant’s total number of known satellites to 29.
A team led by the Southwest Research Institute (SwRI) in Boulder, Colorado, identified the previously unknown moon using the James Webb Space Telescope (JWST), according to a recent NASA press release. The detection was made during an observation on Feb. 2, 2025.
The new moon, provisionally designated S/2025 U1, is estimated to be just 6 miles (10 kilometers) in diameter. Its small size likely rendered it invisible to NASA’s Voyager 2 spacecraft during its 1986 flyby as well as to other telescopes less powerful than JWST. It orbits Uranus at a distance of about 35,000 miles (56,330 km) from the planet’s center, placing it between the orbits of Ophelia and Bianca. This makes it the 14th moon discovered within the complex system of small satellites orbiting closer to the planet than its five largest moons: Miranda, Ariel, Umbriel, Titania, and Oberon.
“This object was spotted in a series of ten 40-minute long-exposure images,” said Maryame El Moutamid, a lead scientist at SwRI, in the press release. “It’s a small moon but a significant discovery.”
Uranus is notable for its numerous small inner moons, which exhibit a complex interplay with the planet’s rings. This dynamic suggests a turbulent past that “blurs the boundary” between a ring system and a moon system, noted team member Matthew Tiscareno of the SETI Institute.
This discovery comes shortly after another uranian moon, S/2023 U1, was discovered in November 2023 by Scott Sheppard of the Carnegie Institution for Science using the Magellan Telescopes in Chile. At only 5 miles (8 km) across, it is likely the smallest of the planet’s moons.
Uranus was the first planet discovered with a telescope, by William Herschel in 1781. He also found its two largest moons, Titania and Oberon, in 1787. The planet’s other three major moons were discovered by 1948.
The discovery of moons in our solar system dates back to 1610, when Galileo Galilei first observed Jupiter’s four largest satellites. As of early 2025, there are over 890 confirmed moons in the solar system, according to NASA. While most are named for mythological figures, Uranus’ moons are uniquely named for characters from the works of William Shakespeare and Alexander Pope.
The discovery of S/2025 U1 highlights the advanced capabilities of JWST.
“Looking forward, the discovery of this moon underscores how modern astronomy continues to build upon the legacy of missions like Voyager 2,” El Moutamid said. “Now, nearly four decades later, the James Webb Space Telescope is pushing that frontier even farther.”
