- calendar_today August 16, 2025
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The James Webb Space Telescope (JWST) has discovered an unexpected new moon around Uranus, one of the most mysterious ice giants in our solar system. The discovery brings the known number of Uranus’ moons to 29, and likely many more will be found.
The dim object was unveiled on Feb. 2 in a series of 40-minute-long exposure images taken by Webb’s Near-Infrared Camera (NIRCam). The moonlet is just 6 miles (10 km) wide and is among the tiniest natural satellites known around Uranus, a planet where it’s so small that its size and the bright emission of Uranus’ rings probably hid it from previous missions and telescopes. Even NASA’s Voyager 2 spacecraft, which flew by Uranus almost 40 years ago, was unable to spot it.
“This is a small moon but an important discovery,” said Maryame El Moutamid, a lead scientist at the Southwest Research Institute’s Solar System Science and Exploration Division in Boulder, Colorado. El Moutamid is also the Webb project’s principal investigator for a program dedicated to Uranus’ rings and inner moons. “It demonstrates how Webb is extending what we have learned about the solar system from previous missions by orders of magnitude,” El Moutamid added.
The new moon is temporarily named S/2025 U1 and orbits Uranus at a distance of about 35,000 miles (56,000 km) from the planet’s center. It travels in a nearly circular path in Uranus’ equatorial plane, wedged between the known moons Ophelia just outside the planet’s main ring system and Bianca. Its proximity to its current location hints that it could have formed in place.
The moon is dark, very small, and moving relatively quickly, making it difficult to distinguish it from Uranus’ glare and its bright rings. The problem is compounded because, with its 6-mile (10-km) wide diameter, it is quite small for a moon but huge for a ring particle. Webb’s ability to capture faint infrared light is what led astronomers to detect it. “Webb has already revealed tantalizing views of Uranus’ rings, weather, and atmosphere, and this discovery adds to that impressive record,” El Moutamid said.
More Clues to Uranus’ Rings
Its discovery not only adds another member to Uranus’ ringed family of moons, but it also may give more clues about the origin of the ring system itself. Scientists think the new satellite S/2025 U1 and parts of Uranus’ rings could be related, perhaps fragments of the same ancient breakup event. “The discovery also raises questions about how many more such small moons remain hidden around Uranus and how they interact with its rings,” El Moutamid added.
Uranus has five major moons—Miranda, Ariel, Umbriel, Titania, and Oberon—plus a group of small satellites. The new body becomes the 14th inner small moon, in a system with more small inner moons so close to one another than on any other planet, a fact that confounds astronomers. The satellites are so close together that their orbits should cross, yet somehow, they don’t. Scientists believe they might be acting as shepherds, containing Uranus’ narrow rings.
“Extremely exciting new tiny moon inside the Uranus ring system detected by James Webb. I helped discover one of Uranus’ moons last year, so I’m super happy to see the continued effort and success in the Uranus program,” said Scott Sheppard, an astronomer at the Carnegie Institution for Science, who was not part of the new study, but who co-discovered a Uranus moon in 2024. He added, “It’s a very significant discovery since it is so closely associated with Uranus’ inner ring system. A very small object like this is impossible to detect by anything but Webb.”
“The discovery of this new inner moon further blurs the line between the moons and the rings of Uranus. Their complex inter-relationships hint at a chaotic history,” said Matthew Tiscareno of the SETI Institute, Webb Uranus project co-principal investigator. “This new moon is smaller and fainter than the smallest inner moons we previously knew about around Uranus. This also means there are likely more satellites hiding in Uranus’ rings waiting to be found.”
Planetary history
New moons around Uranus have been added one by one over time. The five moons that are largest have been known for a long time, with the earliest discoveries dating to 1787. Voyager 2 made the first discovery of additional moons during its historic 1986 flyby and found 10 new Uranus moons. These ranged from 16 to 96 miles (26 to 154 km) across in diameter. Ground-based telescopes and the Hubble Space Telescope later discovered another 13 small moons, all 8 to 10 miles (12 to 16 km) in diameter and darker than asphalt. The inner moons, those orbiting closer to the planet than the big five moons, are typically ice and rock, while those outside of Oberon are thought to be captured asteroids.
The future of Uranus exploration may soon expand significantly. A planetary decadal survey report published in 2022 by the National Academies of Sciences, Engineering, and Medicine, recommended a Uranus Orbiter and Probe mission as NASA’s next large planetary endeavor, with a potential launch in the early 2030s. However, the proposed mission may not find the money in the years of budget debates to come. The probe would study Uranus’ extreme tilt in rotation, its mysterious magnetic field, its atmospheric dynamics, and could search for worlds with icy oceans in the moons.
