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Astronomers using NASA’s James Webb Space Telescope (JWST) have discovered a previously unseen moon orbiting Uranus, one of the planet’s largest ringed moons that Voyager 2 also missed. The new small satellite brings the number of known Uranian moons to 29, but researchers think there are more waiting to be found.

The new object was discovered Feb. 2 in a series of 40-minute long-exposure images taken by Webb’s Near-Infrared Camera, the same instrument that first detected faint rings around the ice giant earlier this year. Only about 6 miles (10 kilometers) across, the new satellite is one of the smallest natural satellites ever discovered around Uranus. The small moon’s tiny size and the intense light coming from Uranus’ rings likely masked its existence from past missions and telescopes. NASA’s Voyager 2 spacecraft, which made history by flying by Uranus nearly 40 years ago, also missed it.

“This is a small moon, but a significant discovery,” said lead scientist Maryame El Moutamid, of the Southwest Research Institute’s Solar System Science and Exploration Division in Boulder, Colorado, and principal investigator of a Webb program studying Uranus’ rings and inner moons. “Webb has taken our knowledge way beyond what was possible by previous missions.”

S/2025 U1 is about 35,000 miles (56,000 kilometers) from the center of Uranus, follows a nearly circular orbit in the planet’s equatorial plane, and orbits between known moons Ophelia just outside Uranus’ main ring system and Bianca, which may have formed near its current position.

Because the small moon is dark, tiny, and moves quickly against the bright glare of Uranus and its rings, astronomers struggled to tease it apart. Webb was able to see the dim object thanks to its ability to detect faint infrared light. The space telescope has already given scientists their first glimpses of Uranus’ rings, weather, and atmosphere, and this latest detection builds on that impressive record.

Unlocking Uranus’ Mysterious Moons and Rings

In addition to expanding the family of Uranus’ natural satellites, the discovery may also help astronomers learn more about the history of Uranus’ ring system. Scientists think the small satellite S/2025 U1 and portions of Uranus’ rings may have been formed by the same ancient event and may be fragments of the same object. “The discovery of this new moon raises questions about how many other small moons remain to be discovered around Uranus and how they interact with its rings,” El Moutamid added.

Uranus now has five major moons — Miranda, Ariel, Umbriel, Titania, and Oberon — and a collection of small satellites. The newly discovered body is the 14th small moon in the inner system. No other planet has as many small inner moons all so close to one another, and astronomers don’t understand why. The orbits of these satellites are so close that they should cross one another’s paths, but somehow, they’re all in stable orbits. Astronomers think the small moons may shepherd Uranus’ narrow rings, keeping them in line.

“It’s very exciting to have a new moon discovered at Uranus, especially since this object is very near the inner ring system, where the moons are at their densest,” said Scott Sheppard, an astronomer at the Carnegie Institution for Science who was not involved in the new study but co-discovered another Uranus moon in 2024. “It’s a testament to the amazing sensitivity of Webb.”

The SETI Institute’s Matthew Tiscareno, co-principal investigator in the Webb Uranus project, says the new find blurs the line between Uranus’ moons and its rings. “Their complex inter-relationships hint at a chaotic past,” he said. Tiscareno and El Moutamid plan to continue refining the new moon’s orbit and searching for more hidden moons.

The new object is even smaller and fainter than the three smallest known Uranian inner moons, so it’s likely there are more to be found. “Satellites the size of a few kilometers in diameter remain undiscovered, especially when it comes to Uranus, because it’s very hard to find small things near the bright glare of the planet,” Sheppard said. “You can either use long-exposure images with Webb or you need to send a spacecraft to find them.”

The discovery of the new satellite, like so many of Uranus’ past moons, will be announced in the Minor Planet Electronic Circular, an online publication of the International Astronomical Union’s Minor Planet Center. That circular will also include images and other details about the moon, and the team plans to release additional observations, refined orbits, and more data about the new moon in the coming weeks and months.

In the future, scientists expect to discover even more Uranian moons, satellites, and rings. In a planetary decadal survey published in 2022, the National Academies of Sciences, Engineering, and Medicine recommended that NASA’s next large planetary science mission be a Uranus Orbiter and Probe, and it could launch in the early 2030s. Budget discussions have left that mission’s funding uncertain, but a Uranus Orbiter and Probe would study Uranus’ tilted rotation, complex magnetic field, atmospheric dynamics, and potential icy ocean worlds on some of its moons.

El Moutamid and her team plan to use Webb to further refine the newly discovered moon’s orbit, and to keep looking for more hidden moons around Uranus. “Discovering a new moon around Uranus helps scientists to better understand how its strange system formed and provides context for its rings, while also preparing us for future missions to Uranus like NASA’s Uranus Orbiter and Probe,” El Moutamid said.