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The James Webb Space Telescope (JWST) has revealed a new moon orbiting Uranus. It was detected on February 2 by a series of long-exposure images taken with the Near-Infrared Camera over a period of about 40 minutes.

The moon is just 6 miles (10 km) wide. It is one of the smallest known natural satellites of Uranus and likely remained hidden from previous missions and ground-based telescopes because it is both so small and dark, and because Uranus’ rings glow brightly. Even NASA’s Voyager 2 spacecraft, which flew by the ice giant almost 40 years ago, did not detect 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. El Moutamid is also the principal investigator of a Webb program that is observing Uranus’ rings and inner moons. “The discovery illustrates how Webb is transforming our understanding in ways no previous mission could,” she said.

The newfound moon, temporarily named S/2025 U1, is about 35,000 miles (56,000 km) from Uranus’ center, following a nearly circular orbit in the planet’s equatorial plane, nestled between the known moons Ophelia, just outside the planet’s main ring system, and Bianca. The moon likely formed near where it is now, the scientists said.

Astronomers could not easily separate its image from Uranus and its bright rings because it is dark, tiny, and moving quickly. But Webb can detect faint infrared light, and in the case of S/2025 U1, that was enough to do the job. The telescope has already teased out details of Uranus’ rings, weather, and atmosphere, and the discovery adds to that impressive record.

The discovery of the new Uranus moon is important not only because it adds one more to the family of natural satellites around the ice giant, but also because it provides insights about the origin of Uranus’ unusual ring system. It is possible, the scientists said, that S/2025 U1 and parts of Uranus’ rings formed at the same time, and from the same event, such as the break-up of a larger object.

“The discovery also raises questions about how many more small moons remain hidden around Uranus and how they interact with its rings,” El Moutamid added.

At the moment, Uranus is known to have five major moons—Miranda, Ariel, Umbriel, Titania, and Oberon—as well as a clump of much smaller satellites. The discovery is the 14th small moon found in this inner system. No other planet has as many small inner moons bunched up so close together, a fact that has long puzzled astronomers.

These satellites are so close that their orbits are at risk of crossing, yet somehow they have not. Astronomers think the satellites may be acting as shepherds, keeping Uranus’ narrow rings in check. “The new moon was discovered by the James Webb Space Telescope, and it is very exciting,” said Scott Sheppard, an astronomer at the Carnegie Institution for Science who did not participate in the new research but who co-discovered a Uranus moon in 2024. “It is also particularly exciting because it is very close to Uranus’ inner ring system.”

The SETI Institute’s Matthew Tiscareno, co-principal investigator in the Webb Uranus program, said the discovery of S/2025 U1 “is yet another example where we find that the distinction between Uranus’ moons and its rings is really blurred.”

“Their complex inter-relationships with each other hint at a chaotic history,” Tiscareno said. “The fact that this moon is even smaller and fainter than the smallest known Uranian inner moons also suggests that many more are out there and still await discovery.”

In past decades, astronomers have gradually uncovered Uranus’ moons. Before Voyager 2’s historic close-up in 1986, only five moons had ever been spotted (the big ones), and discoveries date back as far as 1787. Voyager 2 detected 10 more moons during its flyby, ranging in size from 16 to 96 miles (26 to 154 km) in diameter. Ground-based telescopes and the Hubble Space Telescope would later find another 13 small moons, between 8 and 10 miles (12 and 16 km) across and even darker than asphalt. Moons in the inner system are likely to be composed of ice and rock. Moons orbiting beyond Oberon are suspected to be captured asteroids.

The future could bring even more Uranus exploration, potentially. In a planetary decadal survey published in 2022 by the National Academies of Sciences, Engineering, and Medicine, a Uranus Orbiter and Probe mission was recommended as NASA’s next big planetary endeavor. The mission could launch in the early 2030s, but funding is not yet certain as NASA debates budget requests. Such a mission would investigate Uranus’ unusual axial tilt, peculiar magnetic field, atmospheric dynamics, and whether or not any of its moons might be icy ocean worlds.

Sheppard said he suspects that more moons as small as a few kilometers are waiting to be discovered either through long-exposure imaging from telescopes like Webb or from spacecraft missions to the planet. El Moutamid and her team will refine the orbit of S/2025 U1 with more observations and continue the hunt for other, as-yet hidden moons.

“Discovering a new moon around Uranus helps scientists better understand how its strange system formed, learn more about its rings, and prepare for future missions such as NASA’s Uranus Orbiter and Probe,” El Moutamid said.