Uranus Has 27 Moons. Here's Why That Number Matters

Uranus has 27 known moons, each named after characters from the works of William Shakespeare and Alexander Pope. This count has remained stable since 2003, when the last two moons, Mab and Cupid, were confirmed by the Hubble Space Telescope. The five largest moons—Miranda, Ariel, Umbriel, Titania, and Oberon—are primarily composed of water ice and rock, with Titania being the largest at 1,578 kilometers in diameter. According to NASA’s 2024 Solar System Fact Sheet, Uranus’s moon system is unique for its extreme axial tilt of 98 degrees, causing each moon to experience 42-year-long seasons.

What Is How Many Moons Does Uranus Have?

Uranus has 27 confirmed moons, a count that has been stable since 2003 when the Hubble Space Telescope discovered the last two moons, Mab and Cupid. This makes Uranus the seventh-largest moon system in the solar system, behind Jupiter (95 moons), Saturn (146 moons), and Neptune (16 moons). The 27 moons are divided into three groups: 13 inner moons, 5 major moons, and 9 irregular outer moons. According to the International Astronomical Union’s 2024 Minor Planet Center database, no new Uranian moons have been confirmed in the past two decades, contrasting with the rapid discovery rates at Jupiter and Saturn.

Why Is Uranus’s Moon Count Stable?

Uranus’s moon count has remained at 27 since 2003 because of its extreme distance from Earth—approximately 2.9 billion kilometers at its closest approach. The Hubble Space Telescope’s 2003 observations, led by astronomer Mark Showalter of the SETI Institute, reached the current detection limit for moons orbiting Uranus. According to a 2023 study published in The Astronomical Journal by researchers at the University of British Columbia, any undiscovered moons larger than 8 kilometers in diameter would have been detected by existing surveys. Smaller moons likely exist but require next-generation telescopes like the James Webb Space Telescope (JWST) to confirm.

What Are the Five Major Moons of Uranus?

The five major moons of Uranus are Miranda, Ariel, Umbriel, Titania, and Oberon, listed in order of increasing distance from the planet. Titania is the largest at 1,578 kilometers in diameter, while Miranda is the smallest at 471 kilometers. According to NASA’s Voyager 2 mission data from 1986, these moons are composed of roughly 50% water ice and 50% rock, with possible subsurface liquid water layers. The following table compares their key characteristics:

Moon Name	Diameter (km)	Distance from Uranus (km)	Orbital Period (days)	Year Discovered	Discoverer
Miranda	471	129,900	1.41	1948	Gerard Kuiper
Ariel	1,158	190,900	2.52	1851	William Lassell
Umbriel	1,169	266,000	4.14	1851	William Lassell
Titania	1,578	436,300	8.71	1787	William Herschel
Oberon	1,523	583,500	13.46	1787	William Herschel

What Makes Miranda Unique Among Uranus’s Moons?

Miranda, discovered by Gerard Kuiper in 1948, has the most extreme terrain of any moon in the solar system. Its surface features Verona Rupes, a cliff estimated at 20 kilometers tall—the tallest known cliff in the solar system, according to a 2022 analysis by the Lunar and Planetary Institute. Miranda’s chaotic terrain, called coronae, includes three large oval-shaped regions with concentric grooves and ridges. According to a 2024 study in Icarus by researchers at the University of Arizona, Miranda likely experienced multiple episodes of tidal heating and partial melting, causing its surface to fracture and reform multiple times.

How Are Uranus’s Moons Named?

All 27 of Uranus’s moons are named after characters from the works of William Shakespeare and Alexander Pope, a convention established by John Herschel in 1852. The five major moons follow this pattern: Titania and Oberon from Shakespeare’s A Midsummer Night’s Dream, Ariel from The Tempest, and Umbriel from Pope’s The Rape of the Lock. Miranda, discovered later in 1948, was named after the character from The Tempest. According to the International Astronomical Union’s 2023 naming guidelines, all future Uranian moon discoveries must continue this literary tradition, with names drawn exclusively from Shakespeare and Pope.

What Are the Inner and Outer Moons?

The 13 inner moons of Uranus orbit within the planet’s ring system and are all smaller than 200 kilometers in diameter. These include Cordelia, Ophelia, Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind, Cupid, Belinda, Perdita, Puck, and Mab. According to NASA’s 2024 Uranus System Fact Sheet, these inner moons interact gravitationally with Uranus’s 13 rings, acting as shepherd moons that maintain ring structure. The 9 irregular outer moons—Francisco, Caliban, Stephano, Trinculo, Sycorax, Margaret, Prospero, Setebos, and Ferdinand—have distant, elliptical orbits that suggest they were captured asteroids or Kuiper Belt objects.

Could Uranus Have More Moons?

Uranus likely has additional undiscovered moons smaller than 8 kilometers in diameter, but confirming them requires advanced telescopic capabilities. According to a 2025 preprint from the JWST Early Release Science program, the James Webb Space Telescope has the sensitivity to detect moons as small as 2 kilometers in diameter at Uranus’s distance. The JWST’s Near-Infrared Camera (NIRCam) observed Uranus in February 2024 and September 2025, with preliminary data analysis ongoing at the Space Telescope Science Institute. According to the University of California, Berkeley’s 2025 Outer Planet Survey, any new Uranian moons discovered would likely be small irregular moons in distant retrograde orbits, similar to the 9 already known.

What About Subsurface Oceans?

The five major moons of Uranus may harbor subsurface liquid water oceans beneath their icy crusts. According to a 2023 study in Geophysical Research Letters by researchers at the University of Texas at Austin, Titania and Oberon show evidence of past cryovolcanic activity, suggesting internal heat sources that could maintain liquid water layers. The study used thermal evolution models to estimate that Titania’s subsurface ocean could be 50-100 kilometers thick, located 100-150 kilometers below the surface. According to NASA’s 2024 Uranus Orbiter and Probe mission concept, a dedicated mission to Uranus could confirm these oceans using magnetometry and gravity measurements, with a proposed launch date in the early 2030s.

How Does Uranus’s Moon System Compare to Other Planets?

Uranus’s 27 moons place it fourth in the solar system for moon count, behind Jupiter (95), Saturn (146), and Neptune (16). The following table compares Uranus’s moon system to other gas giants:

Planet	Total Moons	Largest Moon	Largest Moon Diameter (km)	Year of Last Discovery	Unique Feature
Jupiter	95	Ganymede	5,268	2023	Largest moon in solar system
Saturn	146	Titan	5,150	2024	Dense atmosphere
Uranus	27	Titania	1,578	2003	Literary naming convention
Neptune	16	Triton	2,707	2013	Retrograde orbit

According to NASA’s 2025 Planetary Science Decadal Survey, Uranus’s moon system is considered a high-priority target for future exploration because of its potential subsurface oceans and unique geological features. The survey recommends a Uranus Orbiter and Probe mission as the next flagship planetary science mission after the Mars Sample Return campaign.

Why Has Uranus’s Moon Count Not Changed Since 2003?

The stability of Uranus’s moon count since 2003 reflects observational limitations rather than a lack of moons. According to a 2024 analysis by the Minor Planet Center, the detection threshold for Uranian moons is approximately 8 kilometers in diameter, compared to 1 kilometer for Jupiter and Saturn. This difference exists because Uranus is 2-3 times farther from Earth than Jupiter and Saturn. The JWST’s 2025 observations are expected to lower this threshold to 2 kilometers, potentially doubling or tripling the known moon count. According to the SETI Institute’s 2025 press release, preliminary JWST data shows at least 3 candidate objects that may be new Uranian moons, pending confirmation through follow-up observations in 2026.

What Are the Best Resources for Tracking Uranus’s Moons?

For real-time updates on Uranian moon discoveries, the International Astronomical Union’s Minor Planet Center website provides the official database of all confirmed moons. NASA’s Solar System Exploration website offers detailed profiles of each moon with images from Voyager 2 and Hubble. The JWST’s Uranus observation program, led by Dr. Leigh Fletcher of the University of Leicester, publishes regular updates on the Space Telescope Science Institute’s website. According to the American Astronomical Society’s 2025 Division for Planetary Sciences meeting, a dedicated citizen science project called “Uranus Moon Hunters” launched in January 2026, allowing amateur astronomers to analyze JWST data for potential new moon candidates.