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Images from NASA’s James Webb Space Telescope (JWST) reveal a previously unknown moon around Uranus. The discovery increases the total number of known moons around the ice giant to 29. Scientists expect more to be hiding in Uranus’ system as well.

Webb revealed the tiny, faint world on February 2 in a series of 40-minute-long-exposure images. The new moon is about 6 miles (10 km) across, making it one of the smallest natural satellites to be discovered around Uranus. Its faintness, along with the glare from Uranus’ rings, likely hid it from detection during previous missions and by telescopes on Earth. NASA’s Voyager 2 spacecraft, which flew past Uranus 38 years ago, 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. El Moutamid is also the Webb program’s principal investigator (PI), and her team is studying Uranus’ rings and inner moons. “I’m glad that people get the importance of this tiny moon as it shows how Webb is opening a new era of discoveries, far beyond the capabilities of previous missions.”

Webb discovered the moon, nicknamed S/2025 U1 (pronounced ‘Son 2025 U 1′), about 35,000 miles (56,000 km) from the center of Uranus. It orbits nearly circular and in the plane of Uranus’ equator, nestled between the inner moons Ophelia, just beyond the planet’s main ring system, and Bianca. It has an orbit that suggests it may have formed in its current position.

But it was difficult to spot against Uranus and its rings because it’s so small, dark, and moving quickly. Webb’s ability to see faint infrared light through that glare allowed it to spot S/2025 U1. The telescope has previously given tantalizing hints of Uranus’ rings, as well as its weather and atmosphere. This discovery is one in a string of new observations about Uranus that build on that record.

“It gives us one more piece of this incredible system, and we’re in the middle of a very active time as far as discoveries go,” El Moutamid said.

Curiosity Over Uranus’ Intricate System

The system’s current known major moons are Miranda, Ariel, Umbriel, Titania, and Oberon, which are large icy satellites that were known before Voyager 2’s flyby. The new moon brings the total number of small moons in Uranus’ inner system to 14. No other planet in the solar system has as many small moons that are as close to each other as Uranus’ inner moons are. Astronomers are not sure how these tiny satellites have remained so closely packed in that area or how they haven’t disrupted each other’s orbits. One idea is that they may be shepherds, which are objects that keep the planet’s narrow rings from spreading out and dissipating.

Scott Sheppard of the Carnegie Institution for Science, who was not involved in the new study but helped co-discover a Uranus moon in 2024, called the discovery “very exciting” because of the object’s proximity to Uranus’ inner ring system. He said it will be of great interest for the planetary science community and hailed Webb’s sensitivity for making the discovery possible.

But funding is not yet guaranteed as agency leaders and Congress debate budget priorities. El Moutamid and her team expect to continue following up on the discovery by further refining the object’s orbit, and hopefully detecting more as the team continues to scour the system.

“We are now aware of S/2025 U1, another small moon hidden in Uranus’ rings, in the far reaches of our solar system,” El Moutamid said. “Discovering a new moon around Uranus helps scientists better understand how this peculiar system formed, it provides clues about the origins of the planet’s rings and their interactions with these moons, and helps prepare us for future missions such as NASA’s Uranus Orbiter and Probe mission.”