Uranus, the seventh planet from the Sun, is classified as an ice giant due to its composition of water, methane, and ammonia ices in a supercritical phase. This distant world hosts a complex system of 29 confirmed natural satellites orbiting its highly tilted axis. These moons range from tiny, dark bodies sharing the planet’s orbital plane to large objects with highly irregular paths.
The Current Official Moon Count
The discovery of Uranus’s moon system has spanned centuries, relying on progressively more powerful telescopes and probes. The first two satellites, Titania and Oberon, were spotted by William Herschel in 1787. Ariel and Umbriel were identified by William Lassell in 1851, followed by Gerard Kuiper’s discovery of Miranda in 1948. The pivotal moment occurred during the Voyager 2 flyby in 1986, which revealed 10 previously unseen, small inner moons. Since then, advanced ground-based telescopes and the Hubble Space Telescope began identifying small, faint, irregular moons starting in 1997. Most recently, the James Webb Space Telescope identified a new small inner moon, S/2025 U1, in 2025.
The Five Major Satellites
Uranus’s five largest moons—Miranda, Ariel, Umbriel, Titania, and Oberon—are thought to have formed in an accretion disk around the planet. Titania and Oberon are the largest of the group; Titania has a diameter of approximately 1,578 kilometers, making it the biggest moon in the system. Titania shows evidence of ancient geological activity, including large rift valleys, while Oberon is heavily cratered with dark material visible on the floors of its craters.
Miranda, the innermost and smallest of the five, has a highly fractured, patchwork surface. This jumbled terrain includes enormous fault canyons and distinct, chevron-shaped features known as coronae, suggesting a chaotic geological history. Ariel has the brightest and possibly youngest surface, displaying an extensive network of valleys and fault systems. This faulting and the relative lack of large impact craters may point to past cryovolcanic activity, where icy-liquid material erupted onto the surface. Umbriel stands out as the darkest of the five, with an ancient, heavily cratered surface that shows minimal signs of internal geological activity.
The Inner and Irregular Moons
The remaining satellites are categorized into two groups based on their orbital characteristics: the small inner moons and the distant irregular moons. The 14 inner moons orbit close to Uranus, residing within the planet’s narrow ring system. These satellites are small, dark, and share a common origin with the rings, likely being fragments of a larger, shattered body.
Two inner moons, Cordelia and Ophelia, function as “shepherd moons” for the outermost epsilon ring, maintaining its sharply defined edges through gravitational influence. Their orbits are considered chaotic, suggesting that collisions and orbital changes are possible over long timescales. Far beyond the major satellites are the ten irregular moons, characterized by highly eccentric and strongly inclined orbits. Most of these distant moons follow a retrograde path, orbiting the planet in the opposite direction of Uranus’s rotation. These irregular satellites are thought to be captured asteroids or comets, which explains their dark, carbonaceous composition and non-conforming orbits.