The James Webb Space Telescope has uncovered a new moon orbiting Uranus, spotted during a set of observations on 2 February 2025.
“This object was spotted in a series of 10 40-minute long-exposure images captured by the Near-Infrared Camera (NIRCam),” said Maryame El Moutamid, lead scientist in the Southwest Research Institute’s Solar System Science and Exploration Division. “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.”
The moon is estimated to be about six miles, or 10 kilometres, across. Its faintness explains why it escaped earlier detections. Voyager 2, which passed Uranus in 1986, managed to reveal 11 moons and two new rings but missed this one.
Orbit and neighbours
The new moon, provisionally named S/2025 U1, travels some 35,000 miles (56,000 kilometres) from the planet’s centre.
“It’s located about 35,000 miles (56,000 kilometers) from Uranus’ center, orbiting the planet’s equatorial plane between the orbits of Ophelia (which is just outside of Uranus’ main ring system) and Bianca,” El Moutamid said. “Its nearly circular orbit suggests it may have formed near its current location.”
That orbit places it among the inner cluster of moons, inside the larger paths of Miranda, Ariel, Umbriel, Titania and Oberon. Uranus now counts 14 inner moons in total.
Complexity among rings and moons
“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, 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.”
Uranus is surrounded by 13 narrow rings. Some scientists believe they were shaped by small “shepherd” moons, whose gravity holds the material in place. The latest discovery is not a shepherd moon, but astronomers think its existence adds another piece to the puzzle.
Over time, inner moons may have collided and spread into rings, before coalescing back into new moons. For S/2025 U1, “this is the most likely scenario,” said El Moutamid, who added the process may have taken place within the last 50 million years.
What comes next
The International Astronomical Union will decide on an official name. So far, all Uranian moons take their names from the works of Shakespeare or Alexander Pope. El Moutamid confirmed the team has a suggestion but said the approval process must be followed.
Follow-up observations will refine the moon’s size and composition, and astronomers expect Webb to find even smaller satellites. “We were very happy to see it,” said El Moutamid. “It was acting exactly like a moon.”
Building on Voyager 2’s legacy
The 1986 flyby of Voyager 2 remains the only direct visit to Uranus. It offered more than 7,000 images and transformed knowledge of the ice giant, but much was left unexplored.
“Through this and other programs, Webb is providing a new eye on the outer solar system,” said El Moutamid. “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. 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 Jan. 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.”
Uranus remains one of the least explored worlds in the solar system. Its moons and rings are thought to hold vital clues about planetary formation, not only in our neighbourhood but also for the many ice giants orbiting other stars.
Uranus “is just waiting for us to know more about it,” said El Moutamid. “We need to go there, study it, to better understand our universe.”
“This object was spotted in a series of 10 40-minute long-exposure images captured by the Near-Infrared Camera (NIRCam),” said Maryame El Moutamid, lead scientist in the Southwest Research Institute’s Solar System Science and Exploration Division. “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.”
The moon is estimated to be about six miles, or 10 kilometres, across. Its faintness explains why it escaped earlier detections. Voyager 2, which passed Uranus in 1986, managed to reveal 11 moons and two new rings but missed this one.
Orbit and neighbours
The new moon, provisionally named S/2025 U1, travels some 35,000 miles (56,000 kilometres) from the planet’s centre.
“It’s located about 35,000 miles (56,000 kilometers) from Uranus’ center, orbiting the planet’s equatorial plane between the orbits of Ophelia (which is just outside of Uranus’ main ring system) and Bianca,” El Moutamid said. “Its nearly circular orbit suggests it may have formed near its current location.”
That orbit places it among the inner cluster of moons, inside the larger paths of Miranda, Ariel, Umbriel, Titania and Oberon. Uranus now counts 14 inner moons in total.
Complexity among rings and moons
“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, 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.”
Uranus is surrounded by 13 narrow rings. Some scientists believe they were shaped by small “shepherd” moons, whose gravity holds the material in place. The latest discovery is not a shepherd moon, but astronomers think its existence adds another piece to the puzzle.
Over time, inner moons may have collided and spread into rings, before coalescing back into new moons. For S/2025 U1, “this is the most likely scenario,” said El Moutamid, who added the process may have taken place within the last 50 million years.
What comes next
The International Astronomical Union will decide on an official name. So far, all Uranian moons take their names from the works of Shakespeare or Alexander Pope. El Moutamid confirmed the team has a suggestion but said the approval process must be followed.
Follow-up observations will refine the moon’s size and composition, and astronomers expect Webb to find even smaller satellites. “We were very happy to see it,” said El Moutamid. “It was acting exactly like a moon.”
Building on Voyager 2’s legacy
The 1986 flyby of Voyager 2 remains the only direct visit to Uranus. It offered more than 7,000 images and transformed knowledge of the ice giant, but much was left unexplored.
“Through this and other programs, Webb is providing a new eye on the outer solar system,” said El Moutamid. “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. 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 Jan. 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.”
Uranus remains one of the least explored worlds in the solar system. Its moons and rings are thought to hold vital clues about planetary formation, not only in our neighbourhood but also for the many ice giants orbiting other stars.
Uranus “is just waiting for us to know more about it,” said El Moutamid. “We need to go there, study it, to better understand our universe.”
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