Moons of Uranus

Discover facts about Uranus’s moons, when they were discovered, who they’re named after, which are the biggest and smallest.

By Russell Deeks

Published: Monday, 05 February 2024 at 08:33 AM

Uranus is currently known to have 27 moons, which can be broken down into three groups. There are 5 major moons, 13 inner moons and nine irregular moons.

Uranus’s 5 largest moons are the planet’s largest by some distance, and are – in order of largest first – Titania, Oberon, Ariel, Umbriel and Miranda.

Miranda is the smallest of Uranus’s major inner moons, while Uranus’s largest moon is Titania, with a radius of 789km.

We’ve known about some of Uranus’s moons since the late 18th century, while others were discovered much more recently – not until 2003, in the case of Margaret – and they vary immensely in terms of size, mass and orbital distance, as can be seen in the table Uranus’s Moons at a glance below.

Uranus’s moons Titania (left) and Oberon (right) in two images captured by Voyager 2. Moons are not to scale. Credit: NASA/JPL

Uranus moons, Shakespeare and Pope

What Uranus’s moons all have in common is that they’re all named after characters from Shakespeare. Well, almost!

The exceptions are Belinda and Umbriel, both of which are named after characters from a poem by Alexander Pope (1688-1744).

Ariel, meanwhile, is a name that appears in works by both Shakespeare AND Pope.

Exactly why Uranus’s moons are named after Shakespearean characters isn’t, however, entirely clear.

Uranus was discovered by William Herschel in 1781, swiftly followed by Titania – Uranus’s largest moon, with a radius of 789km – and Oberon in 1787.

An image of Uranus's moon Umbriel captured by Voyager 2 on 24 January 1986 from a distance of 557,000 kilometers. Credit: NASA/JPL
An image of Uranus’s moon Umbriel captured by Voyager 2 on 24 January 1986 from a distance of 557,000 kilometers. Credit: NASA/JPL

But Herschel himself never named the two satellites, referring to them only as ‘number one’ and ‘number two’.

Nor is there anything in the letters, notes and papers he left behind to suggest Herschel was a lover of Shakespeare.

Rather, it appears to have been his son John Herschel who gave the two moons their names, during his tenure as president of the Royal Astronomical Society.

However, this was around the same time that another astronomer, William Lassell, discovered two more moons – the aforesaid Ariel and Umbriel – in 1851, and there is some debate as to whether it was Herschel or Lassell who came up with the four names.

Voyager Uranus moon discoveries

Uranus's moon Ariel as seen by the Voyager 2 spacecraft. Credit: NASA/JPL
Uranus’s moon Ariel as seen by the Voyager 2 spacecraft. Credit: NASA/JPL

The fifth major moon of Uranus wasn’t discovered until 1948, when Gerard Kuiper (after whom the Kuiper Belt is named) dubbed it Miranda, after a character from The Tempest.

A precedent was now set.

Voyager 2 is so far the only spacecraft to have visited Uranus, when it flew by the planet in 1986.

At that time, Voyager 2 found 10 new moons around Uranus, much smaller than those that had been discovered by astronomers on Earth.

When Voyager 2 discovered a further 10 much smaller moons orbiting Uranus at a much closer distance than the 5 major ones, these too were given Shakespearean names.

Views of Uranus's moons, as seen by Voyager 2. Left to right: Ariel, Uriel, Titania, Oberon. Sizes not to scale. Credit: NASA
Views of Uranus’s moons, as seen by Voyager 2. Left to right: Ariel, Uriel, Titania, Oberon. Sizes not to scale. Credit: NASA

Modern Uranus Moon discoveries

Since the 1980s, astronomers have discovered a further 12 moons at Uranus: 3 more inner moons and 9 tiny, irregular ones that orbit the planet on large, eccentric orbits.

And again, the scientists tasked with naming them turned to the Bard’s Complete Works for inspiration.

Astronomers Brett Gladman and John Kavelaars, for instance, led a team that discovered several Uranian moons in the late 1990s – and they named them carefully.

The first was dubbed Caliban, a character who appears (as the moon had) out of the dark, while Trinculo and Stephano, which both have highly erratic orbits, were named after drunken characters in The Tempest.

Uranus and its 5 brighter moons, imaged in January 2022. Credit: Pete Lawrence
Uranus and its 5 brighter moons, imaged in January 2022. Credit: Pete Lawrence

In 1999, astronomer Erich Karkoschka found another moon around Uranus in the images captured by Voyager 2 some 13 years later, while comparing the spacecraft’s images of the Uranus system with those taken by the Hubble Space Telescope.

Perdita was confirmed as a moon in 2003.

There is much more we still need to learn about Uranus, and who knows if there are yet more small moons out there, just waiting to be discovered?

But for now, here are all the ones we know about…

A view of Uranus, its rings and moons captured by the NIRCam (Near-Infrared Camera) on the James Webb Space Telescope. Credit: NASA, ESA, CSA, STScI
A view of Uranus, its rings and moons captured by the NIRCam (Near-Infrared Camera) on the James Webb Space Telescope. Credit: NASA, ESA, CSA, STScI

Uranus’s moons at a glance

Key stats about all of Uranus’s 27 moons, from largest to smallest.

Titania

Oberon

Umbriel

Ariel

Miranda

Puck

Sycorax

Portia

Juliet

Belinda

Cressida

Caliban

Rosalind

Desdemona

Bianca

Prospero

Setebos

Ophelia

Cordelia

Stephano

Perdita

Fransisco

Ferdinand

Margaret

Cupid

Mab

Trinculo

Notes: