Titania (moon)

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Titania, recorded by Voyager 2 on January 24, 1986
Titania, high resolution colored photo
Central body Uranus
Properties of the orbit
Major semi-axis 436,300 km
Periapsis 435,800 km
Apoapsis 436,800 km
eccentricity 0.0011
Orbit inclination 0.079 °
Orbital time 8.706234 d
Mean orbital velocity 3.87 km / s
Physical Properties
Albedo 0.27 ± 0.03
Apparent brightness 13.49 ± 0.04 mag
Medium diameter 1577.8 ± 3.6 km
Dimensions (3.527 ± 0.09) 10 21 kg
surface 7,820,000 km 2
Medium density 1.711 ± 0.005 g / cm 3
Sidereal rotation 8.706234 days
Axis inclination 0.0 °
Acceleration of gravity on the surface 0.378 m / s 2
Escape speed 773 m / s
Surface temperature −213 ° C to −184 ° C; 60-89 K

Wilhelm Herschel

Date of discovery January 11, 1787
Remarks Possible existing atmosphere
Size comparison between Uranus and its moons
Size comparison between Uranus (left) and its largest moons, from left to right: Puck, Miranda, Ariel, Umbriel, Titania and Oberon (photo montage to scale)

Titania (also Uranus III ) is the seventeenth innermost of the 27 known moons of the planet Uranus and the fourth innermost of the five large moons of Uranus . With a diameter of 1,578 kilometers, Titania is the largest moon of Uranus and after Neptune 's largest moon Triton, the eighth largest moon in the solar system .

Discovery and naming

Titania was discovered on January 11, 1787 together with Oberon as the first and second Uranus moons by the Electorate of Hanoverian astronomer Wilhelm Herschel with his self-made reflecting telescope in Slough ( Great Britain ). Herschel had discovered Uranus around six years earlier. He announced the discovery of the two moons after the orbit parameters had been ascertained on February 9, 1787 and continued to observe the system from 1790 to 1796. Herschel later stated the discovery of another four Uranus moons , which later turned out to be nonexistent. For nearly 50 years after this discovery, Titania and Oberon were not observed by any telescope other than Herschel's.

The moon was named after the elf queen Titania from William Shakespeare's Midsummer Night 's Dream . Titania was Oberon's wife .

All the moons of Uranus are named after characters from Shakespeare or Alexander Pope . The names of the first four Uranus moons discovered ( Oberon , Titania, Ariel and Umbriel ) were proposed in 1852 by John Herschel , son of the discoverer, at the request of William Lassell , who had discovered Ariel and Umbriel a year earlier.

Originally Titania was referred to as "Uranus' first satellite," and in 1848 Lassell's moon was named Uranus I , although he sometimes used Herschel's numbering Uranus II . In 1851 Lassell renumbered the previously known moons according to their distances from the mother planet, and since then Titania has been referred to as Uranus III .

Track properties


Titania orbits Uranus on a prograde , almost perfectly circular orbit at an average distance of around 436,300 km (approx. 17,070 Uranus radii) from its center, i.e. around 410,700 km above its cloud ceiling. The orbit eccentricity is 0.0011, the orbit is inclined 0.079 ° to the equator of Uranus .

The orbit of the next inner moon Umbriel is on average 170,000 km away from Titania's orbit, that of the next outer moon Oberon about 147,000 km.

Titania orbits Uranus in 8 days, 16 hours, 56 minutes and 59 seconds.

Titania's orbit is entirely in the magnetosphere of Uranus. The following hemispheres of (almost) atmospheric moons such as Titania are therefore under constant bombardment by magnetospheric plasma , which rotates with the planet. This can lead to a darkening of the subsequent hemisphere, which has so far been observed in all Uranus moons except for Oberon. Titania also traps magnetospherically charged particles, which leads to an increased number of these particles in its orbit and was observed by the Voyager 2 spacecraft .

Since Titania, like Uranus, practically orbits the sun on its side relative to the rotation, its northern or southern hemisphere points either directly towards the sun or away from it at the time of the solstice , which leads to extreme seasonal effects. This means that the poles of Titania lie in permanent darkness or are illuminated by the sun for half a Uranus year of 42 years. During the solstice, the sun is therefore near the zenith over the poles. During the Voyager-2 flyby in 1986, which occurred almost at the solstice, the southern hemispheres of Uranus and its moons pointed toward the Sun while the northern hemispheres were in complete darkness. During the equinox , when the equatorial plane crosses with the direction to the earth and which also occurs every 42 years, mutual occultations of the Uranus moons and solar eclipses on Uranus are possible. A number of these rare events last took place between 2007 and 2008; Titania was covered by Umbriel on August 15, 2007 and December 8, 2007.

Currently Titania has no orbital resonance with other moons. However, an estimated 3.8 billion years ago, it may have been in 4: 1 resonance with Ariel , possibly responsible for the internal heating of this moon.


The rotation time is the same as the cycle time ; Like the moon of the earth , Titania shows a synchronous rotation , which takes place within 8 days, 16 hours, 56 minutes and 59 seconds. Its axis of rotation is almost exactly perpendicular to its plane .

Physical Properties


Titania has a diameter of 1577.8 km. It is almost the largest moon of Uranus, as it is only about 55 km larger than the second largest moon Oberon . In general, the two moons are very similar.

In terms of size, Titania can best be compared with Oberon or the Saturn moons Rhea and Iapetus . Voyager 2 has so far only been able to investigate about 40% of the entire moon, mainly the southern hemisphere - as with all Uranus moons.

The total area of ​​Titania is about 7,820,000 km 2 , which is slightly more than the area of Australia .

internal structure

Titania has an average density of 1.71 g / cm 3 and its relatively high albedo is 0.27, which means that 27% of the incident sunlight is reflected from the surface. The low density and the high albedo suggest that Titania is composed of around 50% water ice , 30% silicate rock and 20% carbon compounds and other heavy organic compounds. The presence of water ice is supported by infrared spectroscopic studies from 2001 to 2005 that revealed crystalline water ice on Titania's surface. This seems to be more prominent on Titania's leading hemisphere. The reason for this is unknown, but it appears to have come from the bombardment of charged particles from Uranus' magnetosphere, which is more represented in the following hemisphere due to the co-rotation of the plasma. These energetic particles tend to sputter water ice, decompose methane trapped in ice as gas hydrate , and darken other organic matter, resulting in carbon-rich deposits on the surface.

Apart from the water ice, only carbon dioxide (CO 2 ) could be detected spectroscopically without any doubt and this compound is mainly concentrated on the following hemisphere. Its origin has not yet been adequately clarified. It could be produced locally from carbonates or organic matter by the influence of the charged particles of Uranus' magnetosphere, or by solar ultraviolet radiation . The former hypothesis would explain the asymmetry in the distribution, since the following hemisphere is under greater influence from the magnetosphere. Another possible source is the outgassing of original CO 2 trapped in water ice in Titania's interior. The release of CO 2 from the interior may be related to past geological activity of the moon.


Titania is possibly a differentiated body with a rock core and a coat of water ice. If this were the case, the diameter of the core would be 1040 km, which corresponds to 66% of the total diameter, and a core mass of 58% of the total mass - these parameters are given by the composition of the moon. The pressure in the center of Titania is about 5.8 kbar . The water-ice-rock mixture and the possible presence of salt or ammonia  - which lower the freezing point of water - indicate that an underground ocean like the one on Jupiter's moon Europa could possibly exist between the core and ice mantle of Titania . The depth of this ocean would be around 50 km in this case, the temperature would be around −83 ° C (190 K). The current internal structure depends heavily on Titania's thermal history, which is not well known.


Titania, photomontage of two photos of the Voyager 2 spacecraft from a distance of 369,000 kilometers

The surface of Titania has numerous craters, but far fewer than on its outer neighbor Oberon, as well as relatively freshly formed ice fields, huge canyons and crust breaks. This suggests geological activity after the moon was formed.

Of the major moons of Uranus, Titania lies in its brightness between the dark moons Umbriel and Oberon and the lighter moons Ariel and Miranda . The surface shows great brightness effects depending on the lighting angle; the reflectivity of 0.35 at a phase angle of 0 ° drops rapidly to 0.25 at around 1 °. The spherical albedo is a relatively low 0.17.

The surface shows a slightly reddish color, but less reddish than Oberon. The relatively fresh ice fields are bluish, while the rolling plains on the leading hemisphere appear a little redder near Ursula Crater and along some of the trenches. There appears to be a small dichotomy between the leading and trailing hemispheres; the latter appears about 8% more reddish. This difference corresponds to the gentle levels and can be a coincidence. possibly originated from the weathering by charged particles and impacts of micrometeorites since the formation of the solar system . The color asymmetry probably arose from the accretion of reddish material from the outer uranus system, possibly from irregular moons , which would predominantly be reflected on the leading hemisphere.

The mean surface temperature on Titania is −203 ± 7 ° C (70 ± 7 K ). The temperature can rise to a maximum of −184 ° C and drop to −213 ° C.

On the surface, the acceleration due to gravity is 0.378 m / s 2 , which corresponds to around 4% of that on earth.

So far, scientists have identified three types of surface structures on the surface known so far: canyons, cliffs and craters. All surface features on Titania are named after female characters and locations from works by William Shakespeare.

Chasmata and Rupes

Messina Chasma from a distance of 500,000 kilometers

The canyons , which are called Chasma (plural Chasmata ), presumably represent rift breaks that have arisen through tectonic expansion processes. They are the result of a global pressure caused by the freezing of water or a water-ammonia solution in the interior of Titania. The Chasmata on Titania are about 20 to 50 km wide and 2 to 5 km deep.

The most noticeable canyon and the most noticeable feature of the surface at all is a huge fracture about 1500 km in length called Messina Chasmata , against which the Grand Canyon looks tiny on earth. This structure consists of two faults that run northwest to southeast and together form an ongoing trench . The canyon system cuts most of the impact craters in its path and is intersected by only a few craters, suggesting a later formation in the history of Titania when the ice crust broke open by an internal expansion.

In terms of its extension, Messina Chasmata is comparable to the Ithaca Chasma on Saturn's moon Tethys ; relative to the total size of the moon, it could also be compared with the Valles Marineris on Mars or Kachina Chasma on Ariel.

The breaks not related to the Chasmata are called rupes ( Latin for cliffs ). The largest and only named of its kind is Rousillon Rupes , which is a terrain level. Since this structure is cut by very few craters, it must therefore also be relatively young.

The areas around some of these fractures appear as smooth planes in the resolution of the Voyager images, possibly later in the history of Titania's surface formation, when most of the existing craters already existed. These deformations may be of an endogenous nature, such as by cryovolcanic ejection of liquid material from the interior, or they may have been leveled by impact material from nearby craters. The moats are probably Titania's most recent surface feature; they cut all the craters and even the plains.

List of named Chasmata and Rupes on Titania
Surname Length (km) Coordinates Origin of name
Messina Chasmata 1492.0 33 ° 18′S 335 ° 00′E / 33.3 ° S 335 ° E Messina ( Italy ), setting in Much Ado About Nothing
Belmont Chasma 305.0 8 ° 30′S 32 ° 36′E / 8.5 ° S 32.6 ° E Belmonte ( Italy ), the setting in The Merchant of Venice
Rousillon Rupes 402.0 14 ° 42′S 23 ° 30′E / 14.7 ° S 23.5 ° E Roussillon ( France ), the setting in All's well that ends well

Crater area

Titania photographed from 500,000 km away. Some large surface details are labeled

The surface of Titania is less cratered than the surfaces of Oberon or Umbriel, which means that it is more recent. The diameters of the craters range from a few kilometers to 326 km for the largest known one named Gertrude . Its crater rim rises about 2 km above the crater floor, and the central mountain has a diameter of about 150 km and is about 2 to 3 km high. The fact that the crater rim and the central mountain are relatively flat compared to the overall size of the crater indicates that it has flattened over time due to later processes.

West of the Gertrude crater is an area with an irregular topography, the Unnamed Basin, which may represent another large, heavily weathered impact basin with a diameter of 330 km.

Some craters, such as the Ursula or Jessica mentioned above , are surrounded by bright deposits of impact material and radiation systems made up of relatively fresh ice. Ursula is surrounded by gentle plains that have the lowest crater densities of the entire moon and must therefore be relatively young. All of the large craters on Titania have flat bottoms and central mountains, with the exception of Ursula, whose center is a depression. Ursula is cut by Belmont Chasma , who must therefore be of even more recent date.

The geology of the surface has been influenced by two competing forces: shaping by impact and endogenous surface renewal. The former took place over the entire period of the history of the moon, while the latter also had a global impact, but only occurred at a certain point in time after the formation of Titania. They leveled the heavily cratered area, which explains the relative scarcity of craters on the surface visible today. Further episodes of renewal may have occurred later and lead to the formation of the planes. However, they could also have been caused by the deposition of the nearby craters. The most recent endogenous processes are mainly of a tectonic nature and caused the formation of the Chasmata, which are huge fractures in the moon's ice crust created by a global expansion of approximately 0.7%.

List of named craters on Titania
Surname Diameter (km) Coordinates Origin of name
Gertrude 326.0 15 ° 48′S 287 ° 06′E / 15.8 ° S 287.1 ° E Gertrude , Hamlet's mother in Hamlet
Ursula 135.0 12 ° 24′S 45 ° 12′E / 12.4 ° S 45.2 ° E Ursula , Hero's chambermaid in Much Ado About Nothing
Mopsa 101.0 11 ° 54′S 302 ° 12′E / 11.9 ° S 302.2 ° E Mopsa , a shepherdess from The Winter's Tale
Calphurnia 100.0 42 ° 24′S 291 ° 24′E / 42.4 ° S 291.4 ° E Calpurnia Pisonis , Caesar's wife from Julius Caesar
Katherine 75.0 51 ° 12′S 331 ° 54′E / 51.2 ° S 331.9 ° E Catherine , Queen of England from Henry VIII
Elinor 74.0 44 ° 48′S 333 ° 36′E / 44.8 ° S 333.6 ° E Eleonore , widow of Heinrich II from King Johann
Jessica 64.0 55 ° 18′S 285 ° 54′E / 55.3 ° S 285.9 ° E Jessica , Shylock's daughter from The Merchant of Venice
Valeria 59.0 34 ° 30′S 4 ° 12′E / 34.5 ° S 4.2 ° E Valeria , Virgilia's friend from Coriolanus
Lucetta 58.0 14 ° 42′S 277 ° 06′E / 14.7 ° S 277.1 ° E Lucetta , Juliet's lady-in-waiting from Two gentlemen from Verona
Bona 51.0 55 ° 48′S 351 ° 12′E / 55.8 ° S 351.2 ° E Bona , sister of the king of Henry VI, part 3
Adriana 50.0 20 ° 06′S 3 ° 54′E / 20.1 ° S 3.9 ° E Adriana , wife of Antipholus from The Comedy of Errors
Marina 40.0 15 ° 30′S 316 ° 00′E / 15.5 ° S 316 ° E Marina , daughter of Pericles from Pericles, Prince of Tire
Phrynia 35.0 24 ° 18′S 309 ° 12′E / 24.3 ° S 309.2 ° E Phrynia , Maitresse of Alcibiades from Timon of Athens
Iras 33.0 19 ° 12′S 338 ° 48′E / 19.2 ° S 338.8 ° E Iras , lady-in-waiting to Cleopatra from Antony and Cleopatra
Imogen 28.0 23 ° 48′S 321 ° 12′E / 23.8 ° S 321.2 ° E Imogen , daughter of Cymbeline from Cymbeline

the atmosphere

The presence of carbon dioxide suggests a thin seasonal atmosphere, similar to that of Jupiter's moon Callisto . Other gases like nitrogen or methane probably don't exist as they would escape into space due to Titania's insufficient gravity. At the maximum temperature of −184 ° C (89 K) during the summer solstice , the vapor pressure is about 3  nBar .

On September 8, 2001, Titania covered the 7.2 mag star HIP 106829 , which was a rare opportunity to determine the diameter and the ephemeris more precisely and to discover any existing atmosphere. The data did not reveal an atmosphere with a pressure greater than 10-20 nBar. If it exists, it is by far thinner than that of Pluto or the Neptune moon Triton . This upper limit is nevertheless several times greater than the maximum possible surface pressure of the carbon dioxide, which means that the measurements were not mandatory for the parameters of the atmosphere.

The special geometry of the Uranus system supplies the poles with more solar energy than the equatorial regions. Since the vapor pressure of CO 2 is a factor in increasing the temperature, this may lead to an accumulation of carbon dioxide in the lower latitudes, where it can firmly exist in the form of dry ice on the regions of higher albedo and shady areas . During the Titania summer, when temperatures can reach 85-90K, carbon dioxide sublimes and migrates to the equatorial regions and the opposite pole, which is a type of CO 2 cycle. The accumulated gas can be removed from the cold traps by magnetic particles, which sputter it away from the surface . Titania is believed to have lost a significant portion of the existing carbon dioxide since it was formed about 4.6 billion years ago.


Titania was probably formed by an accretion disk or by a sub-nebula that may have been around Uranus during its formation or that formed after the (still theoretical) impact that caused the planet to tip over. The exact composition of this sub-nebula is not known, but the higher densities of the Uranus system compared to Saturn's moons closer to the Sun indicate a relative scarcity of water. There may have been significant amounts of nitrogen (N 2 ) and carbon (C) in the form of carbon monoxide (CO) and molecular nitrogen instead of ammonia (NH 3 ) and methane (CH 4 ). Satellites that emerged from such a sub-nebula should contain less water ice and CO and N 2 than gas hydrate enclosed in ice and more rock, which would explain the higher densities.

The accretion process may take several thousand years to complete the formation of Titania. Models show that the impacts accompanying accretion are likely to cause the outer shell of the moon to heat up to a temperature of around 250 K to a depth of up to 60 km. Once formed, this outer layer cooled while the interior of Titania heated up due to the decomposition of radioactive elements in the rock. The cooling outer shell contracted while the interior expanded . This created severe tension in the moon's crust, which resulted in fractures on the crust and the formation of the canyons. This process, which lasted about 200 million years, indicates that the endogenous formation of the surface was completed billions of years ago.

The initial heat of accretion and the subsequent decomposition of radioactive elements may have melted water ice if a substance that depresses the freezing point, such as salt or ammonia, was present in the form of ammonium hydroxide . This should have led to a separation of ice and rock (differentiation) of the core. In this case, a layer of liquid water rich in dissolved ammonia could have formed at the boundary between the mantle and core. The eutectic temperature of this mixture is 176 K. If the temperature has fallen below this value, the existing ocean today should probably have frozen over long ago. This freezing over probably led to the expansion of the interior, which was probably responsible for the formation of the majority of the Chasmata. Knowledge of the development of Titania is currently very limited.


For 200 years since the discovery by William Herschel in 1787, little was known about Titania other than the orbit parameters. The moon was too small and too far away to be resolved with terrestrial telescopes.

On January 20, 1986 Titania has a relatively close distance of a minimum of 365,200 km from the Voyager 2 - spacecraft happened and are photographed and measured. As a result of the high inclination of the planetary system of 98 °, the axes of rotation of Uranus and Titania pointed towards Earth at this point in time, so that the moons of Uranus could not be approached individually on the equatorial plane, as was previously the case with Jupiter and Saturn, but instead Arranged orbits like a target around the planet and the planet had to be hit. This meant that of Uranus and all of its moons, only the southern hemisphere could be photographed at intervals of about two days - the worst possible position for a flyby. In addition, you had to choose a moon, as a close pass by inevitably required large distances to all others.

Since Voyager 2 was to be steered further to Neptune , the prerequisite for this was a close Uranus flyby. As a result, only the moon near Miranda could be passed. As a result, the best resolution of the photos was about 3.4 km; they show about 40% of the surface, whereby only about 24% could be used with the necessary quality for geological maps and crater counting.

Web links

Commons : Titania (moon)  - Collection of images, videos and audio files

Individual evidence

  1. a b Information table and brief description on solarviews.com (English)
  2. ^ William Herschel: An Account of the Discovery of Two Satellites Revolving Round the Georgian Planet. By William Herschel, LLD. FRS Phil. Trans. R. Soc. Lond. January 1, 1787 77: 125-129; doi : 10.1098 / rstl.1787.0016 ( full text )
  3. Uranus and its moons at JPL
  4. Uranus and its moons on meta-evolutions.de