Uranus XXVIII

Uranus XXVIII, originally designated S/2025 U 1, is a tiny moon of Uranus, measuring between 8 and 10 kilometers across. It became the 29th moon found in the Uranian system. Its discovery was announced in August 2025 by a team led by Maryame El Moutamid, who spotted it in images from the James Webb Space Telescope’s NIRCam instrument taken on 2 February 2025.

The moon orbits Uranus at a distance of about 57,844 kilometers from the planet’s center, placing it between the orbits of Ophelia and Bianca. Its orbital period is 9.6 hours. Like Uranus’s other inner moons, its path is nearly circular and lies along the planet’s equatorial plane. Because it is so small, it is extremely faint, with an apparent magnitude of 25.5 in the near-infrared H-band—too dim for the Hubble Space Telescope or the Voyager 2 spacecraft to detect.

The International Astronomical Union’s Minor Planet Center assigned the permanent Roman numeral designation Uranus XXVIII (or Uranus 28) on 24 March 2026. Before that, it was known by the temporary provisional designation S/2025 U 1. Following convention, Uranian moons are named after characters from the plays of William Shakespeare and Alexander Pope, but a proper name has not yet been approved by the IAU. Co-discoverer Mark R. Showalter noted in a 2025 New Scientist article that discussions about a name have occurred, but no shortlist exists.

Uranus XXVIII is the 14th known inner moon of Uranus—small moons that orbit closer to the planet than its five largest moons (Miranda, Ariel, Umbriel, Titania, and Oberon). Its nearly circular orbit, located just outside Uranus’s inner ring system, suggests it formed near its current position, according to El Moutamid.