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.

“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.

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