.

Uranus already has 28 known moons and counting. The newest addition to the planet’s already remarkable system is so small and dark that it probably escaped detection during previous spacecraft missions and even the Hubble Space Telescope. The team announced the discovery on February 2.

“The new moon is tiny — just 6 miles (10 kilometers) across — and incredibly difficult to see next to the much brighter glare of Uranus’ rings,” said Maryame El Moutamid, a lead scientist on the discovery team and a principal investigator at the Southwest Research Institute’s Solar System Science and Exploration Division in Boulder, Colorado. “This is a small moon but a significant discovery that underscores how Webb is not just building on but going beyond what past missions could accomplish.”

El Moutamid and her colleagues were able to separate the moon from the planet’s bright rings and brighter glow because Webb can see faint infrared light emitted by the new moon. It’s the first new satellite spotted by Webb, which was launched in 2021.

“This new moon is one of the smallest natural satellites known around Uranus and could provide some critical clues into the formation and evolution of Uranus’ peculiar ring system,” El Moutamid said in a statement.

Situated about 35,000 miles (56,000 kilometers) from Uranus’ center, the newly discovered moon orbits between two other small moons called Ophelia, just beyond Uranus’ main ring system, and Bianca. It moves in nearly circular orbit within Uranus’ equatorial plane. This is the first time astronomers have spotted a satellite orbiting between Ophelia and Bianca, and its position there indicates that it likely formed near its current location.

“Webb has already shown us glimpses of Uranus’ rings and has given us a better understanding of its weather and atmosphere. This newly discovered moon is yet another discovery for Webb around Uranus that builds on this record,” El Moutamid said.

Unlocking Uranus’ Secrets

The newly discovered moon is small (about 6 miles or 10 kilometers wide) and dark, and orbits Uranus at a speed of about 0.6 miles per second (1 kilometer per second). To separate the moon’s signal from that of Uranus and its rings, the team processed long-exposure images taken over the course of about three hours in February with Webb’s Near-Infrared Camera. The photos showed it to be moving, and in late April, the team calculated its orbit and came up with a name: S/2025 U1, the astronomical convention for small moons orbiting Uranus, where the number is the year of discovery. The team has not yet found an ideal candidate to permanently name the moon. The discovery paper is published in the Astronomical Journal.

A total of five known moons beyond S/2025 U1 — Miranda, Ariel, Umbriel, Titania, and Oberon — make up what scientists call Uranus’ major satellites. They orbit far from the planet and were all discovered before the Voyager 2 spacecraft’s historic flyby of the ice giant in 1986. Uranus also has several small satellites that are much closer to the planet, including the 13 moons that were discovered after Voyager 2, using ground-based telescopes or the Hubble Space Telescope. S/2025 U1 is now the 14th small moon in this inner system.

Five small moons are so close together in Uranus’ inner system that their orbits should cross. For some reason, this is not happening, and scientists think these small satellites shepherd the planet’s narrow rings to keep them in line. “We do not know of another planet that has this many small inner moons orbiting so close to each other,” El Moutamid said in the statement.

Scott Sheppard, an astronomer at the Carnegie Institution for Science who was not involved in the new study but discovered a moon of Uranus with a colleague last year, said in a statement that the find is “very exciting” and that the object is “in such close association with the inner ring system that it is one of the most significant to be found.” He said Webb’s sensitivity makes the discovery all the more remarkable.

“The most fascinating thing is that, no matter how much effort goes into imaging Uranus’ rings and moons, there always seems to be another small moon to find,” Sheppard added.

Scientists are not yet sure what happened to form Uranus’s strange ring and moon system. The new moon is only about 6 miles (10 kilometers) wide, much smaller than the narrow rings it orbits between. The scientists working on the discovery suggest the moon and these narrow rings are “likely related” and may be fragments from the same ancient event that shattered another body, but they do not yet know if the rings are older or younger than the moon. Matthew Tiscareno, co-principal investigator on the Webb Uranus project and a senior scientist at the SETI Institute in Mountain View, California, said in the statement that this discovery underlines the fact that the boundary between Uranus’ rings and moons is unclear.

“The inter-relationships of these components hint at a chaotic history, and we’re only beginning to understand how they evolved,” Tiscareno said. “It’s remarkable to see how small and faint this newly detected moon is compared to the tiniest of Uranus’ known inner moons, which are about 10 miles (16 kilometers) across. Clearly, more satellites remain hidden around Uranus.”

Future of Uranus Exploration

The team is refining the new moon’s orbit and will continue to search for additional satellites.

On April 21, the team is releasing new observations of Uranus’ rings. A new paper studying these features, and hypothesizing the connection between these narrow rings and the new moon, is now available on the arXiv pre-print server.

NASA will explore Uranus even more closely in the future, with a planetary decadal survey published in 2022 by the National Academies of Sciences, Engineering, and Medicine recommending a Uranus Orbiter and Probe mission as the agency’s next large planetary mission. The recommended study would develop the mission concept for potential launch in the early 2030s, pending budget considerations and funding. Uranus’ tipped-over rotation, tilted magnetic field, swirling atmosphere, and possibly icy ocean worlds are on the list of fascinating things to study.