Astronomers detect a tiny new moon near Uranus’s rings with JWST
Using the James Webb Space Telescope’s high-resolution NIRCam instrument, scientists have discovered a new, tiny moon orbiting Uranus, bringing the planet’s known moons to 29. The object, provisionally labeled S/2025 U1, is estimated to be about 10 kilometers (six miles) across, making it one of the smallest bodies found to orbit the ice giant.
The moon was spotted in a series of 10 long exposures—each about 40 minutes—captured by JWST’s Near-Infrared Camera. The observations show S/2025 U1 in close proximity to Uranus’s main ring system, a region that is already a dynamic environment sculpted by the gravity of nearby moons. Unlike the tightly packed rings of Saturn, Uranus’s rings are more widely spaced, with multiple ring groups separated by gaps. Scientists say the presence of such a small moon so close to the rings could help explain how Uranus’s rings are shaped and maintained.
“The cameras on JWST are incredibly sensitive,” one scientist noted, highlighting the telescope’s ability to detect faint objects next to very bright planets. The discovery underscores JWST’s value for Solar System science, not just distant galaxies, and opens new questions about how such small moons form and interact with their ring systems.
Context from the past shows the continuing hunt for Uranian moons: Voyager 2’s 1986 flyby revealed 11 new moons, adding to the ones known at the time, and subsequent observations from Hubble and ground-based telescopes have identified even smaller bodies, some as small as a few tens of kilometers across. The new moon’s tiny size makes it especially challenging to detect, but JWST’s sensitivity allowed the team to confirm its existence.
Researchers are eager to learn more about S/2025 U1, including its color and composition, precise orbit, and how it influences—or is influenced by—the rings. Future observations with JWST and other telescopes may help refine models of Uranus’s ring-moon dynamics and deepen our understanding of how such systems evolve.
In a broader sense, the find demonstrates humanity’s growing ability to map the tiniest members of distant planetary systems, even within our own solar system, and it highlights the ongoing potential of JWST to reveal details that were previously out of reach. This discovery adds another piece to the puzzle of what crafts the striking ring structures around Uranus and how countless small moons silently sculpt the architecture of outer solar system worlds.
Summary: A new 10-km moon near Uranus’s rings, designated S/2025 U1, has been detected by JWST, marking Uranus’s 29th known moon and offering new opportunities to study ring-moon interactions and the small-body population of the outer Solar System.
Commentary and additional value: This milestone reinforces the idea that even in well-studied regions like the Uranian system, there are still many small, faint worlds to uncover. If future observations pin down S/2025 U1’s orbit and composition, scientists can test models of how ring systems are sculpted by nearby moons and how such tiny bodies form and survive in a dynamic environment. A positive takeaway is the continued demonstration of JWST’s versatility—extending well beyond distant distant galaxies to the subtle details of our own planetary neighborhood. If you’re curious, follow-up studies will likely compare this moon’s characteristics with those of other small Uranian moons to map a broader picture of the system’s formation history.