NASA’s Webb telescope spotted a new moon orbiting Uranus

Uranus hosts yet another moon, which looks like a tiny, faint smudge in images captured by the James Webb Space Telescope, researchers report in an Aug. 19 NASA release. The newfound object makes the 29th observed lunar companion for the sideways-tilted ice giant.

“Uranus is a very strange planet,” says planetary scientist Maryame El Moutamid of the Southwest Research Institute in Boulder, Colo. Most of its rings are narrow, just a few kilometers wide, hinting that moons orbiting their edges might constrain the rings’ sizes.

El Moutamid leads a project studying the odd planet’s rings and moons, so in February, she had JWST snap a series of 10 long-exposure images of Uranus over the course of nearly seven hours. 

All the images contained an unknown blurry blotch traveling around Uranus, just beyond the planet’s set of narrow inner rings. The repeated appearances, along with the object’s speed, suggested the faint spot was a newly discovered moon. El Moutamid and colleagues confirmed the lunar companion’s presence by ruling out any other kind of object or an error in the data.

“At first I couldn’t believe it,” El Moutamid says. “It’s the first time I ever discovered a moon — I was really excited.”

The newfound moon, currently called S/2025 U1, is located about 56,000 kilometers away from Uranus’s center, orbiting in a circular path. El Moutamid and colleagues estimate that the moon is roughly 10 kilometers wide, based on comparisons to the planet’s known moons, although the researchers are seeking additional data for a more accurate measurement. S/2025 U1 is smaller and fainter than the 28 other lunar companions, which is probably why past telescopes and the Voyager 2 flyby — equipped with cameras less sensitive than JWST’s — missed the mini moon.

The next step, El Moutamid says, is to submit an official name for the moon to the International Astronomical Union, the organization in charge of naming astronomical objects and their features. S/2025 U1 will be named after a character from the writings of William Shakespeare or Alexander Pope, just like the rest of its lunar siblings. And more might join them soon, El Moutamid says, especially with a NASA Uranus orbiter mission predicted to launch in the 2030s.

“Probably, there are a lot of moons out there,” she says. “They’re just waiting to be discovered.”