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A new moon orbits Uranus, an ice giant planet known for its weirdness. This previously unknown natural satellite was spotted by astronomers using NASA’s James Webb Space Telescope. Researchers think many more tiny moons orbit the planet but remain hidden from view.

The diminutive moon brings the total number of known Uranian moons to 29. Webb’s Near-Infrared Camera, which took long-exposure exposures of the planet and its rings, revealed the faint object on February 2.

The world is only 6 miles (10 kilometers) across. It’s one of the smallest natural satellites discovered to date around Uranus, and the planet’s ring system likely hid it from previous spacecraft and telescopes. Even NASA’s Voyager 2, which flew past Uranus almost 40 years ago, missed the tiny moon.

“This is a small moon, but a significant discovery because it shows just how much Webb is advancing our knowledge beyond previous missions,” said Maryame El Moutamid, a lead scientist at the Southwest Research Institute’s Solar System Science and Exploration Division in Boulder, Colorado, and principal investigator of a Webb program to study Uranus’ rings and inner moons. “We’re not just seeing what we’ve already known about Uranus before – Webb is also unlocking the secrets of moons and rings that we didn’t even know were there.”

The new moon, which has been temporarily named S/2025 U1, is about 35,000 miles (56,000 kilometers) from Uranus’ center. It orbits in the planet’s equatorial plane on a nearly circular path. S/2025 U1 sits between the known moons Ophelia, just outside the main ring system, and Bianca. The small moon likely formed close to its current location.

The moon is dark, tiny, and moves quickly. Astronomers needed a long exposure to tease the faint object away from the glaring light of Uranus and its bright rings. Webb’s ability to see faint infrared light enabled the discovery. The space telescope had already revealed information about Uranus’ rings, weather, and atmosphere.

Solving the Mystery of Uranus’ Moons and Rings

This is not the first new moon astronomers have discovered around Uranus. Voyager 2 alone discovered 10, and the James Webb Space Telescope recently found another.

Uranus is known to have five large moons – Miranda, Ariel, Umbriel, Titania, and Oberon – and a group of 24 small satellites. The newly discovered body is the 14th small moon in Uranus’ inner system. The planet is unique for having so many small inner moons so close together. Astronomers don’t understand how that’s possible because the moons’ orbits are near each other and risk crossing. But they seem to stay stable, and scientists think they may act as shepherds for Uranus’ narrow rings.

“It’s very exciting to see a small new moon in such a close association with Uranus’ inner ring system and rings,” said Scott Sheppard, an astronomer at the Carnegie Institution for Science and co-discoverer of a Uranus moon in 2024 who was not part of the new study. “It’s also very cool Webb has the sensitivity to see these small bodies orbiting the ice giants, especially in regions where they haven’t been seen before.”

Matthew Tiscareno, co-principal investigator in the Webb Uranus project and scientist at the SETI Institute, said the discovery also blurs the line between Uranus’ moons and its rings. “Their complex inter-relationships hint at a chaotic history and bode well for similar discoveries, as the newfound moon is even smaller and fainter than the tiniest known Uranian inner moons,” he said. “The new moon was no easy find and makes me think additional satellites await discovery.”

Astronomers’ understanding of Uranus’ moons has been a slow reveal. Before Voyager 2’s groundbreaking flyby in 1986, the only moons observers had seen were the largest five, with the first discovery dating to 1787. Voyager 2 discovered 10 more moons as it flew by, all of them measuring 16 to 96 miles (26 to 154 kilometers) in diameter. Earth-based telescopes and the Hubble Space Telescope later detected 13 other small moons measuring 8 to 10 miles (12 to 16 kilometers) across and as dark as asphalt. The inner moons are thought to be made of ice and rock, whereas the outer moons beyond Oberon are likely captured asteroids.

The National Academies of Sciences, Engineering, and Medicine released a planetary decadal survey in 2022 that identified a Uranus Orbiter and Probe mission as NASA’s next large planetary venture. If funded, it could launch in the early 2030s, but money is not guaranteed as Congress debates NASA’s budget. This mission would aim to understand Uranus’ tilted rotation, its complex magnetic field, the dynamics of its atmosphere, and potentially even icy ocean worlds among its moons.

Sheppard said there are likely additional moons as small as a few kilometers in diameter to find, either in long-exposure Webb images or with a future spacecraft mission. El Moutamid and colleagues will continue to observe Uranus to refine the orbit of S/2025 U1 and search for more hidden moons.

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