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The James Webb Space Telescope has spotted an unknown moon orbiting Uranus, the ice giant with the backward tilt and a funky ring system. The moon, one of 29 now known to circle Uranus, was first detected Feb. 2 in a series of 40-minute-long exposures from Webb’s Near-Infrared Camera. We can expect to see more of them, as well, the researchers say.

At just 6 miles (10 kilometers) across, the moonlet is one of the smallest natural satellites of Uranus ever discovered. It’s so small and Uranus’ rings are so bright that they likely masked the tiny satellite from previous spacecraft and telescopes. NASA’s Voyager 2 spacecraft, which famously flew by Uranus in 1986, also missed 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, who is also a principal investigator of a Webb program dedicated to observing Uranus’ rings and inner moons. “Webb has already taught us a great deal about Uranus’ rings, weather, and atmosphere, and this discovery shows how Webb will also push our knowledge far beyond what previous missions have been able to do.”

Webb detected the previously unseen moon with a series of long exposures on Feb. 2. The new satellite is currently known as S/2025 U1. It orbits about 35,000 miles (56,000 kilometers) from Uranus’ center, tracing a nearly circular orbit in the planet’s equatorial plane, between known moons Ophelia, just beyond Uranus’ main ring system, and Bianca. The orbital characteristics suggest that the moon may have formed near where it is now.

The dark, tiny, and fast-moving moonlet was hard to spot against the bright glare of Uranus and its rings. In the past, this might have meant astronomers missed it. But Webb could see the faint infrared light the moon emitted, allowing it to detect the moon. Astronomers have been using Webb to peer at Uranus’ rings, weather, and atmosphere. This discovery follows the space telescope’s previous records of Uranus’ rings in different infrared wavelengths and at different angles.

Unlocking Uranus’ Mystery System

“This discovery of a new moon around Uranus is important because it adds another puzzle piece to this very unusual system and raises questions about the origin of Uranus’ ring system,” El Moutamid said. “Could this new moon and parts of the rings share a common origin, perhaps as fragments from the same ancient breakup? The discovery also raises questions about how many more small moons remain hidden around Uranus and how they might be interacting with its rings.”

In addition to five major moons that are among the solar system’s largest satellites — Miranda, Ariel, Umbriel, Titania, and Oberon — Uranus is known to have an entire population of small satellites: the new object is the 14th small moon in that inner system. Uranus is the only planet in the solar system with this many small inner moons. And, oddly, they’re packed so close to one another that their orbits should cross and knock each other out of alignment. And yet, they seem to have a way of not doing so. Astronomers think they may serve as shepherds, corralling Uranus’ narrow rings.

Scott Sheppard, an astronomer at the Carnegie Institution for Science in Washington, D.C., who was not involved in the new study but is a co-discoverer of a Uranus moon this year, said, “This is a very exciting discovery, as it is the first small moon to be found around Uranus since the discovery of the first five large satellites more than 200 years ago, and the properties of this object are particularly interesting. It is very close to the inner ring system of Uranus, and as such is a very important discovery. It is great that Webb is now sensitive enough to discover it.”

“The discovery of this moon, even smaller than the smallest known Uranian inner moons, highlights the fuzzy boundary between Uranus’ moons and rings, and their complex inter-relationships hint at a chaotic history,” said co-principal investigator Matthew Tiscareno of the SETI Institute, who is also part of the Webb Uranus project.