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Using the powerful James Webb Space Telescope (JWST), astronomers have discovered a new moon orbiting Uranus. With the find, the ice giant now has 29 known moons, and researchers say there could be more.

The discovery was made on February 2 with a series of 40-minute long-exposure images from Webb’s Near-Infrared Camera. The new moon is only 6 miles (10 km) across, making it one of the smallest natural satellites yet seen around Uranus. Its proximity to the planet’s bright rings and the fact that it is dark probably hid it from previous flybys and telescopes. Even NASA’s Voyager 2 spacecraft, which swept past Uranus nearly 40 years ago in a historic flyby, failed to detect it.

“This is a small moon but a significant discovery,” said Maryame El Moutamid, a lead scientist at Southwest Research Institute’s Solar System Science and Exploration Division in Boulder, Colorado. El Moutamid is also the principal investigator (PI) of one of the Webb programs observing Uranus’ rings and inner moons. She noted that the discovery is a great example of how Webb is revealing information much deeper than the work done by previous missions.

The new moon is now being referred to as S/2025 U1, but it has yet to be given a formal name. The provisional designation means it is the first newly discovered moon around Uranus (S) in 2025. The body orbits Uranus at a distance of about 35,000 miles (56,000 km) from the planet’s center. It is in a nearly circular orbit in Uranus’ equatorial plane. The new moon is found between two previously known moons, Ophelia, just outside the planet’s main ring system, and Bianca. The location suggests that the object formed where it is now.

The new moon is dark, small, and moves fast. This made it difficult to distinguish it from the glare of Uranus and its rings. Webb was able to detect it with its infrared sensitivity. Faint light from the moon is an infrared signature, and Webb can see it. The telescope is already revealing details about Uranus’ rings, weather, and atmosphere. With this discovery, Webb is building on that record.

Opening a Window on Uranus’ System

This discovery is an exciting addition to Uranus’ moons, but it also has researchers wondering more about the planet’s ring system. S/2025 U1 could be related to one of Uranus’ rings. Researchers think the moon and a part of the planet’s rings may have had a common origin. In other words, fragments from one event now make up the moon and a ring. “The discovery raises questions about how many more small moons remain hidden around Uranus and how they interact with its rings,” El Moutamid said.

Uranus has five major moons: Miranda, Ariel, Umbriel, Titania, and Oberon. There is also a group of smaller satellites, and the newly discovered natural satellite is now the 14th small moon in that inner group. “No other planet has as many small inner moons that are packed in so close to one another, and we don’t understand how that can be,” El Moutamid said. Uranus’ moons are so close to each other that some of their orbits cross paths. That makes them unstable, yet somehow, the moons stay in place. Scientists think the moons are acting as shepherds to Uranus’ narrow rings.

For Scott Sheppard, an astronomer at the Carnegie Institution for Science not involved in the new research but who co-discovered one of Uranus’ moons in 2024, the discovery is “very exciting.” He said that the object is very close to Uranus’ inner ring system and is most likely associated with that structure. “It’s really amazing what Webb can detect in terms of very sensitive, long-exposure imaging,” Sheppard said.

The SETI Institute’s Matthew Tiscareno, co-PI in the Webb Uranus project, noted that “the discovery of this small moon blurs the line between Uranus’ moons and rings.” He explained, “We have only scratched the surface of this ring-moon system; their complex inter-relationships hint at a chaotic history. This discovery is even smaller and fainter than the smallest known Uranian inner moons, implying more undiscovered satellites.”

The story of Uranus’ moons has been an evolution. Before Voyager 2’s iconic flyby in 1986, only the five big moons had been observed, with the first found in 1787. Voyager 2 discovered 10 moons measuring 16 to 96 miles (26 to 154 km) in diameter on its flyby. Later ground-based telescopes and the Hubble Space Telescope found another 13 small moons, each 8 to 10 miles (12 to 16 km) across and as dark as asphalt. The inner moons are thought to be made of ice and rock. In contrast, the moons beyond Oberon are suspected to be captured asteroids.

But researchers plan to continue opening new windows into Uranus. In a planetary decadal survey released by the National Academies of Sciences, Engineering, and Medicine in 2022, a Uranus Orbiter and Probe mission was selected as NASA’s next large planetary science mission. That mission could fly to Uranus in the early 2030s. As of this writing, the mission is unfunded and in budget discussions. The mission would search for clues to Uranus’ tilted rotation, its off-kilter magnetic field, the dynamics of its atmosphere, and what ice ocean worlds may exist among the moons.

Sheppard said there are likely other moons that are kilometers in size yet to be detected, either with long-exposure Webb imaging or a spacecraft mission. El Moutamid and her team plan to continue refining the orbit of S/2025 U1 and keep looking for more hidden moons.

“Discovering a new moon around Uranus helps us better understand how its weird system formed and sheds light on its rings, moons, and interaction with moons and prepares us for future missions like NASA’s Uranus Orbiter and Probe,” El Moutamid said.