NASA’s James Webb Space Telescope has found a previously unknown moon orbiting Uranus.
NASA announced the discovery on Tuesday, adding that the moon was first spotted on Feb. 2. Scientists estimate that the newly discovered moon is about six miles in diameter. Its “tiny” size is likely why other telescopes—and the Voyager 2 spacecraft that conducted a flyby nearly four decades ago—hadn’t caught sight of it before, according to NASA. By comparison, Earth’s Moon has a mean diameter of more than 2,000 miles, and Uranus’ largest moon, Titania, has a diameter of roughly 1,000 miles.
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“It’s a small moon but a significant discovery,” Maryame El Moutamid, a lead scientist in the Southwest Research Institute’s Solar System Science and Exploration Division, said in NASA’s announcement.
Before this discovery, Uranus—the seventh planet from the Sun—was known to have 28 moons. The planet’s moons have often been dubbed the “literary moons” because they’re all named after characters from works by William Shakespeare and Alexander Pope. The planet has five major moons: Miranda, Ariel, Umbriel, Titania, and Oberon.
The new moon, which brings Uranus’ total number of known moons to 29, is currently designated at S/2025 U1 but doesn’t have an official name yet. A name will need to be approved by the International Astronomical Union, which is responsible for naming and designating astronomical objects, according to NASA. The space agency added that the discovery hasn’t yet gone through the peer-review process.
Before this year, the most recently discovered moon, designated at S/2023 U1, was sighted in November 2023.
Matthew Tiscareno, a member of the research team who is part of the SETI Institute, said in NASA’s announcement that the latest discovery makes “it likely that even more complexity remains to be discovered” when it comes to the moons orbiting Uranus.
“There’s probably a lot more of them and we just need to keep looking,” Tiscareno told The Associated Press.