Using NASA’s James Webb Space Telescope, scientists have discovered a previously unknown moon orbiting Uranus, increasing the planet’s known satellite count to 29. This significant finding was made during an observation on February 2, 2025, by a team led by the Southwest Research Institute (SwRI).
“This object was spotted in a series of ten 40-minute long-exposure images captured by the Near-Infrared Camera (NIRCam),” said Maryame El Moutamid, a lead scientist in SwRI’s Solar System Science and Exploration Division based in Boulder, Colorado. “It’s a small moon but a significant discovery, which is something that even NASA’s Voyager 2 spacecraft didn’t see during its flyby nearly 40 years ago.”
Discovery Details and Significance
The newly discovered moon, designated S/2025 U1, is estimated to be just six miles (10 kilometers) in diameter, assuming it has a similar reflectivity (albedo) to Uranus’s other small satellites. This tiny size likely rendered it invisible to Voyager 2 and other telescopes.
“No other planet has as many small inner moons as Uranus, and their complex inter-relationships with the rings hint at a chaotic history that blurs the boundary between a ring system and a system of moons,” said Matthew Tiscareno of the SETI Institute in Mountain View, California, a member of the research team.
“Moreover, the new moon is smaller and much fainter than the smallest of the previously known inner moons, making it likely that even more complexity remains to be discovered.”
Technical Insights and Observational Techniques
This timelapse animation shows the newly discovered moon of Uranus, designated S/2025 U1, as well as 13 of the 28 other known moons orbiting the planet. The observations by NASA’s James Webb Space Telescope’s NIRCam were taken over the course of about six hours on February 2, 2025, under program ID 6379 (principal investigator: M. El Moutamid). The animation is comprised of data taken with NIRCam’s wide band F150W2 filter, which transmits infrared wavelengths from about 1.0 to 2.4 microns.
Due to the drastic differences in brightness levels, the animation is a composite of three different treatments of the data, allowing the viewer to see details in the planetary atmosphere, the surrounding rings, and the orbiting moons. Credit for the animation goes to J. DePasquale (STScI).
Position and Potential Naming
The new moon is the 14th member of the intricate system of small moons orbiting inward of the largest moons, Miranda, Ariel, Umbriel, Titania, and Oberon. All the moons of Uranus are named after characters from Shakespeare and Alexander Pope.
“It’s located about 35,000 miles (56,000 kilometers) from Uranus’s center, orbiting the planet’s equatorial plane between the orbits of Ophelia (which is just outside of Uranus’s main ring system) and Bianca,” said El Moutamid. “Its nearly circular orbit suggests it may have formed near its current location.”
A name for the newly found moon will need to be approved by the International Astronomical Union (IAU), the leading authority in assigning official names and designations to astronomical objects.
Implications for Future Research
“Through this and other programs, Webb is providing a new eye on the outer solar system. This discovery comes as part of Webb’s General Observer program, which allows scientists worldwide to propose investigations using the telescope’s cutting-edge instruments,” said El Moutamid. “The NIRCam instrument’s high resolution and infrared sensitivity make it especially adept at detecting faint, distant objects that were beyond the reach of previous observatories.”
“Looking forward, the discovery of this moon underscores how modern astronomy continues to build upon the legacy of missions like Voyager 2, which flew past Uranus on January 24, 1986, and gave humanity its first close-up look at this mysterious world. Now, nearly four decades later, the James Webb Space Telescope is pushing that frontier even farther.”
The announcement comes as a testament to the capabilities of the James Webb Space Telescope, which continues to unveil the mysteries of our solar system and beyond, promising more groundbreaking discoveries in the near future.
