Queen of Uranus' moons
Titania
Moon of Uranus · discovered 1787 by William Herschel
Titania is the largest of Uranus' many moons and the eighth-largest moon in the Solar System, measuring about 1,580 kilometres across. Its icy grey surface is pocked with craters and split by enormous fault valleys, some more than a thousand kilometres long.
Those fractures tell the story of a moon that once stretched and cracked from the inside. Today, Titania is a leading candidate in the Uranus system for a hidden layer of liquid water — one of the reasons scientists are eager to return.
Key facts
- Diameter
- 1,577 km45% of Earth's Moon
- Mass
- 3.40 × 10²¹ kg
- Surface gravity
- 0.367 m/s²0.037 g
- Density
- 1,662 kg/m³
- Distance from Uranus
- 435,910 km≈ 17.1 Uranus radii
- Orbital period
- 8.71 daysSame as its rotation (tidally locked)
- Discovered
- 1787William Herschel
- Surface
- Water ice, carbon dioxide ice and darker carbon-rich material
- Atmosphere
- None detected; a 2001 occultation set a very low upper limit
- Surface temperature
- Roughly −190 °C to −210 °C
- Rotation
- Synchronous — always shows the same face to Uranus
- Named after
- Queen of the fairies in A Midsummer Night's Dream
Values follow NASA/JPL planetary satellite parameters: mean diameter, mean distance (semi-major axis) and sidereal orbital period.
Surface and geology
Titania's most dramatic feature is Messina Chasmata, a system of fault valleys running for around 1,500 kilometres across the moon — nearly the moon's own diameter. These canyons are grabens, blocks of crust that dropped down between parallel faults as the surface was pulled apart, and their sharp walls suggest they are relatively young in geological terms.
Titania has plenty of craters, but fewer large ones than Oberon or Umbriel, hinting that parts of its surface were resurfaced after the earliest bombardment. The largest known crater, Gertrude, is roughly 325 kilometres wide, while the smaller crater Ursula is cut by later faults. Features are named after female characters from Shakespeare, and canyons after places in his plays.
Some craters are surrounded by bright rays of freshly exposed ice. Telescopic observations also show carbon dioxide ice concentrated on the trailing hemisphere, which may come and go with Titania's long seasons.
Interior and composition
Titania is thought to be roughly half water ice and half rock, probably differentiated into a rocky core and icy mantle. The widespread faulting may have formed as water inside the moon froze and expanded, cracking the crust above.
If any Uranian moon still has an ocean, many scientists think Titania is among the most likely. NASA-led modelling published in 2023 suggested that a layer of salty, ammonia-rich water could survive at the boundary between core and mantle, though this remains a hypothesis awaiting measurement.
Orbit and rotation
Titania orbits Uranus in just under nine days, travelling on a nearly circular path in the planet's equatorial plane. It is tidally locked, so the same hemisphere always faces Uranus.
With Uranus tilted by about 98 degrees, Titania endures seasons lasting about 21 years each, with every pole spending roughly 42 years in continuous sunlight and then 42 years in darkness. Its orbit lies within Uranus' magnetosphere, which bathes the trailing hemisphere in charged particles.
Origin
Titania probably formed in a disc of gas, ice and dust around the young Uranus, possibly material thrown out by the giant impact thought to have knocked the planet on its side. Heat from radioactive decay in its rocky core and from its formation could have melted parts of the interior early on, driving the differentiation and later freezing that cracked its crust.
Exploration
Voyager 2 remains the only spacecraft to have visited Titania. Because Uranus' southern hemisphere faced the Sun in 1986, the flyby imaged only around 40 per cent of the moon's surface.
Discovery (1787)
William Herschel discovered Titania on 11 January 1787, the same night he found Oberon, six years after he had discovered Uranus itself. His son John later proposed the moons' Shakespearean names.
Voyager 2 (1986)
Voyager 2's January 1986 flyby revealed Messina Chasmata, Gertrude crater and other fault systems, providing the only close-up images of Titania to date.
Stellar occultation (2001)
When Titania passed in front of a star in 2001, astronomers measured its size precisely and found no sign of an atmosphere, ruling out anything more than an extremely thin one.
Future missions
The proposed Uranus Orbiter and Probe, the top flagship priority of the 2023–2032 planetary science decadal survey, would map Titania and search for its possible ocean.
The moons of Uranus
Surprising facts about Titania
- Titania is the largest moon of Uranus, yet it is less than half as wide as Earth's Moon — about 1,580 kilometres compared with 3,475.
- Messina Chasmata runs for roughly 1,500 kilometres, almost as long as Titania is wide.
- Titania and Oberon were found on the same January night in 1787 by William Herschel, but the names were only proposed decades later by his son John.
- Carbon dioxide ice on Titania may migrate with the seasons, sublimating in decades-long summer sunlight and refreezing in the long winter dark.
- Titania's total surface area, about 7.8 million square kilometres, is roughly the same as the land area of Australia.