- calendar_today August 16, 2025
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An international team of astronomers using NASA’s James Webb Space Telescope (JWST) has discovered a previously unseen moon orbiting Uranus. The find increases the count of known Uranus’ moons to 29, and there may be more to come.
An image of the new satellite appeared on Feb. 2 in Webb’s long-exposure image mosaics, which are stitched together from 40-minute-long exposures taken by the Near-Infrared Camera (NIRCam) on board the space telescope. The newly discovered body is only 6 miles (10 km) wide, making it one of the smallest natural satellites to orbit Uranus ever found. Small satellites this close to Uranus, and the bright rings in particular, have easily been overlooked in past missions and telescope surveys, including by NASA’s Voyager 2 spacecraft when it flew past Uranus 39 years ago this year.
“This is a small moon, but a very important discovery,” said Maryame El Moutamid, a lead scientist at the Southwest Research Institute’s Solar System Science and Exploration Division in Boulder, Colorado. El Moutamid is also the principal investigator of a Webb program to image Uranus’ rings and study the structure and composition of the planet’s inner moons. “This discovery is particularly special to me because it shows how Webb is taking our understanding of the Uranian system to places that were not reached before by other missions.”
The new moon, temporarily named S/2025 U1, is located about 35,000 miles (56,000 km) from the center of Uranus. It orbits the planet nearly face-on, or in the planet’s equatorial plane, between the two known moons Ophelia (just outside the main ring system) and Bianca. Astronomers say its orbit is nearly circular, which could mean that it formed near where it is now.
Its size and distance from Uranus are only part of the problem in identifying this new moon. It is also dark, so tiny, and fast-moving relative to the planet that astronomers had a hard time pulling its signal apart from the glare of the planet and its bright rings. Webb’s ability to detect faint infrared light was key to unlocking the puzzle. Webb has already peered into Uranus’ rings, weather, and atmosphere, and this discovery adds to that growing record.
Unraveling Uranus’ Mysterious System
The discovery of S/2025 U1 not only increases the total number of known moons around Uranus but also may have implications for understanding the origin of the planet’s rings. Astronomers suspect S/2025 U1 may share a connection with portions of Uranus’ rings and that they may be fragments left over from the same event in the ancient past. “This discovery raises many questions about how many other small moons remain undiscovered around Uranus, how they formed, and how they interact with its rings,” El Moutamid added.
To date, five major moons are known to orbit Uranus: Miranda, Ariel, Umbriel, Titania, and Oberon. In addition, a group of small satellites also orbits the planet. The newly discovered object is now the 14th moon on that short list. Uranus has more small, inner moons packed into the closest orbits than any other planet, and that is something that puzzles astronomers. These satellites are so close together that their orbits cross, and yet somehow they all remain in stable orbits. Scientists suspect they shepherd the planet’s narrow rings.
Astronomer Scott Sheppard of the Carnegie Institution for Science, who did not participate in the new study but co-discovered a moon around Uranus last year, called the new find “very exciting,” in a statement. He also noted the object’s close connection with Uranus’ inner ring system is “what makes it particularly special.” He also praised Webb for its sensitivity.
“The discovery of S/2025 U1 by the Webb team is also a great example of how NASA is building on the success of Voyager to look for the unseen,” said SETI Institute’s Matthew Tiscareno, co-principal investigator in the Webb Uranus program, in a statement. “The discovery blurs the lines between the natural satellites and the rings of Uranus. Their complex inter-relationships hint at a chaotic history,” Tiscareno said. He added that the newly discovered moon was even smaller and fainter than the smallest known Uranian inner moons, which “suggests there are more hidden satellites waiting to be found.”
To date, moons around Uranus have been revealed in a series of steps. Before Voyager 2’s groundbreaking 1986 flyby, only five moons had been discovered, the five largest moons. The first four were discovered in the 1780s by the astronomer William Herschel, who went on to discover Uranus. In 1986, Voyager 2 discovered 10 new moons that were between 16 and 96 miles (26 and 154 km) across. Finally, ground-based telescopes and the Hubble Space Telescope in the 21st century discovered another 13 small moons with diameters of 8 to 10 miles (12 to 16 km) and are so dark that they are believed to be darker than asphalt. Inner moons are made of a mixture of ice and rock, while outer moons outside of Oberon are thought to be captured asteroids.
In the future, human exploration of Uranus may grow considerably. In a planetary decadal survey published in 2022 by the National Academies of Sciences, Engineering, and Medicine recommended that NASA’s next big planetary mission be a Uranus Orbiter and Probe. The probe could launch in the early 2030s, though the mission is competing for funding with other missions in NASA’s budget. The mission would aim to study Uranus’ tilted rotation, complex magnetic field, atmospheric dynamics, and possible icy ocean worlds among the moons.
“Finding a new moon around Uranus not only helps scientists better understand how its strange system formed,” she said, “but also shines light on its rings and will help prepare for future missions like NASA’s Uranus Orbiter and Probe mission.”
