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Astronomers have discovered a new, unknown moon orbiting the ice giant Uranus with NASA’s James Webb Space Telescope (JWST). The seventh planet from the Sun already hosts an unusual collection of moons, and this small satellite brings the known total to 29, though there are likely more.

Webb revealed the ultradistant object on Feb. 2 through a series of 40-minute-long-exposure images taken with its Near-Infrared Camera. At just 6 miles (10 km) wide, the newfound moonlet is one of Uranus’ tiniest natural satellites yet identified. Small size and bright background light from Uranus’ rings likely hid the new object from previous spacecraft and telescopes. NASA’s Voyager 2 space probe, which made its closest approach to Uranus nearly four decades ago, did not spot it.

“This is a small moon, but a significant discovery,” said lead scientist Maryame El Moutamid, a senior research scientist in the Southwest Research Institute’s Solar System Science and Exploration Division in Boulder, Colo. El Moutamid is also the principal investigator of a Webb program that is studying Uranus’ rings and its inner moons. “The fact that this moon escaped detection until now really emphasizes how Webb is bringing knowledge of the Solar System forward and beyond previous explorations,” she said.

A temporary designation of S/2025 U1 has been assigned to the newly found moon, which orbits at a distance of about 35,000 miles (56,000 km) from Uranus’ center. It follows a nearly circular orbit in the planet’s equatorial plane, in the region of space between the two known moons Ophelia (orbiting just beyond the planet’s main ring system) and Bianca. “It orbits in about the same region where it may have formed,” El Moutamid said.

The small satellite’s orbit suggests it likely formed near its current location.

Because the moon is dark, tiny, and moves rapidly across the sky, astronomers had to struggle to distinguish it from the bright glare of Uranus and its rings. Webb’s ability to spot faint infrared light, combined with its other capabilities, led to its discovery. The telescope has previously revealed intriguing details about the planet’s rings, weather, and atmospheric composition, and this new find is one of a series of discoveries that Webb has made in the Uranus system.

Moon Reveals Mystery of Uranus’ Rings

The moon’s discovery adds one more member to Uranus’ extensive family of satellites. It also highlights another mystery about the ice giant: the origin of its complicated ring system. S/2025 U1 could hold clues about that, as well as how the planet’s rings and moons work together, scientists said. “The discovery raises questions about how many more small moons remain hidden around Uranus and how the unknown moons might interact with its rings,” El Moutamid said.

The ring system is so far known to consist of 13 narrow rings. Uranus has five major moons—Miranda, Ariel, Umbriel, Titania, and Oberon—as well as a retinue of smaller satellites. The newly identified small body is now the 14th member of the inner system. No other planet has so many small inner moons so close to one another, a fact that puzzles astronomers. The small satellites orbit so close to one another that their paths risk crossing, yet somehow their orbits remain stable. Scientists suspect that some act as shepherds, confining Uranus’ narrow rings.

“The discovery is very exciting, especially given the association of the newly discovered satellite with Uranus’ inner ring system,” said Scott Sheppard, an astronomer at the Carnegie Institution for Science in Washington, D.C., who was not involved in the new study but discovered a Uranus moon in 2024. “It is just beyond the main ring system,” he continued, “and Webb is so sensitive that we could detect it.”

“Uranus has long blurred the boundary between moons and rings, and this discovery is another example,” said SETI Institute’s Matthew Tiscareno, who is also a co-principal investigator in the Webb Uranus program. “Their complex inter-relationships hint at a chaotic history,” he added. The newly detected moon is even smaller and fainter than the tiniest known Uranian inner moons that the team had already detected in past observations, which hints that there are more to be found.

Uranus has revealed its moons one at a time, over the decades and even centuries. Before Voyager 2’s groundbreaking close encounter in 1986, only the five largest moons had been known, with the earliest discoveries dating back to 1787. Voyager 2 discovered 10 more moons during its flyby, each 16 to 96 miles (26 to 154 km) wide. Observations from ground-based telescopes and Hubble subsequently turned up another 13 small moons, each 8 to 10 miles (12 to 16 km) across and darker than asphalt. The inner moons are thought to be a mixture of ice and rock, while the outer moons beyond Oberon may be captured asteroids.

Future missions to Uranus are on the horizon. NASA’s planetary decadal survey, published by the National Academies of Sciences, Engineering, and Medicine in 2022, recommended that NASA’s next large planetary mission be a Uranus Orbiter and Probe. It could fly in the early 2030s, although its funding is in doubt while NASA grapples with a divisive planetary science budget. If it eventually flies, the spacecraft would study Uranus’ tilted rotation, complex magnetic field, atmospheric dynamics, and other intriguing features, including the potential presence of icy ocean worlds among its moons.

Astronomer Scott Sheppard suspects that more moons await discovery, probably small enough to be only a few kilometers across. They can be found either with Webb’s long-exposure imaging, he said, or by future spacecraft flybys. El Moutamid and her team will be refining the orbit of S/2025 U1 and searching for additional hidden moons.

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