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Scientists have found a new moon circling Uranus with the James Webb Space Telescope, bringing the total number of moons around the ice giant to 29. It may not be alone; other, yet-to-be-discovered moons could also lurk in the system, the team suggests.

The newly revealed satellite was identified on February 2 based on a sequence of 40-minute long-exposure images obtained by Webb’s Near-Infrared Camera. It is only 6 miles (10 km) wide, one of the smallest natural satellites ever found around Uranus. Its diminutive size and the dazzling brightness of Uranus’ rings likely hid it from previous missions and telescopes. The Voyager 2 spacecraft, which flew by Uranus in 1986, may have also overlooked the moon.

“This is a small moon but an important discovery,” said Maryame El Moutamid, an astronomer and lead scientist at the Southwest Research Institute’s Solar System Science and Exploration Division, Boulder, Colorado. “It shows what Webb can do. It’s a step beyond what Voyager 2 was capable of, so we are now able to observe moons in the Uranus system that we didn’t see before.”

El Moutamid, also principal investigator of a Webb program to study Uranus’ rings and inner moons, added that the discovery is expected to “lead us to find more that we did not know about,” and to “gain insight on how many more small moons there are” and how they may interact with Uranus’ ring system.

The new moon, provisionally labeled S/2025 U1, orbits Uranus at a distance of about 35,000 miles (56,000 km) from the planet’s center. It moves in a nearly circular path within the planet’s equatorial plane between two other known moons: Ophelia, just outside the planet’s main ring system, and Bianca. The new moon’s orbit indicates that it may have formed in its current neighborhood.

The new moon remained hidden because it is dark, tiny, and moving quickly. As a result, astronomers had trouble distinguishing the object in images from the glare of the planet’s rings and disk. Webb detected the object by revealing its faint infrared light. Webb had already started revealing details about Uranus’ rings, weather, and atmosphere, and the discovery continues this record.

Moons and Rings of Uranus

The moon discovery also has major implications for the ice giant’s mysterious ring system. Astronomers think that S/2025 U1 may have a common origin with parts of the planet’s rings. These natural satellites may be fragments from an ancient collision or disruption.

“The discovery raises questions about how many more small moons remain hidden around Uranus and how these moons interact with the ring system,” El Moutamid noted.

Uranus now has five large moons, Miranda, Ariel, Umbriel, Titania, and Oberon, as well as a group of smaller satellites. The newly found object is the 14th known small moon within the inner system. It is not yet clear why Uranus has more small inner moons in such proximity to each other than any other planet. These satellites are close enough that their orbits should cross each other, but some still manage to stay stable. Astronomers think that some may shepherd Uranus’ narrow rings.

The discovery was “very exciting,” said Scott Sheppard, an astronomer at the Carnegie Institution for Science, who was not involved in the new study but co-discovered a new Uranus moon in 2024. The object “has an orbit that is tightly linked to the planet’s inner ring system, so I think it is particularly significant,” he noted, and praised Webb’s sensitivity to enable the discovery.

In contrast, the SETI Institute’s Matthew Tiscareno, a co-principal investigator in the Webb Uranus program, stated that “this discovery helps us blur the line between Uranus’ moons and its rings.”

“Their complicated inter-relationships hint at a violent past,” he added, “In fact, this newfound object is even smaller and fainter than the smallest known Uranian inner moons, making it likely that other such satellites remain hidden.”

Uranus’ moons are found in two zones, inner and outer. The ice giant’s nine large satellites are distributed between the two areas. Astronomers think that the inner moons, including the newly found one, are mostly ice and rock; the outer ones, past Oberon’s orbit, are likely captured asteroids.

Four decades ago, Voyager 2 revealed 10 small moons, measuring between 16 and 96 miles (26 and 154 km) wide. The large moons date back to the beginning of systematic observations; the first was spotted in 1787, and the other four were added by Voyager 2. Meanwhile, astronomers have later found 13 other small moons with ground-based telescopes and the Hubble Space Telescope. These satellites are 8 to 10 miles (12 to 16 km) wide and darker than asphalt.

More Uranus Exploration in the Offing

Looking forward, another spacecraft may be coming to Uranus. The planetary decadal survey that the National Academies of Sciences, Engineering, and Medicine published in 2022 recommended a Uranus Orbiter and Probe mission as NASA’s next large planetary program. NASA could send a spacecraft to the ice giant in the early 2030s if it gets funding as Congress works on a federal budget. However, its costs remain unclear. A future mission could explore Uranus’ strange axial tilt, oddly shaped magnetic field, atmospheric dynamics, and perhaps even an icy ocean world among its moons.

Scott Sheppard is positive there is more to come. More small moons in the few-kilometer range are expected to be lurking in Uranus’ shadows. He says these “should be revealed by long-exposure Webb images in the coming years and should be even easier for future spacecraft missions to detect.”

El Moutamid and her team will further refine the new object’s orbit and seek more hidden satellites.

“Discovering a new moon around Uranus helps us understand how the odd system formed and sheds light on the planet’s rings and what else is out there, preparing us for future missions, such as NASA’s Uranus Orbiter and Probe,” El Moutamid said.