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Titania (), also designated Uranus III, is the largest of the
moons of Uranus Uranus, the seventh planet of the Solar System, has 27 known moons, most of which are named after characters that appear in, or are mentioned in, the works of William Shakespeare and Alexander Pope. Uranus's moons are divided into three groups: t ...
and the eighth largest moon in the
Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...
at a diameter of . Discovered by
William Herschel Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline ...
in 1787, it is named after the queen of the fairies in Shakespeare's ''
A Midsummer Night's Dream ''A Midsummer Night's Dream'' is a comedy written by William Shakespeare 1595 or 1596. The play is set in Athens, and consists of several subplots that revolve around the marriage of Theseus and Hippolyta. One subplot involves a conflict a ...
''. Its orbit lies inside
Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus ( Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars), grandfather of Zeus (Jupiter) and father of ...
's
magnetosphere In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior d ...
. Titania consists of approximately equal amounts of ice and rock, and is probably differentiated into a rocky
core Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (manufacturing), used in casting and molding * Core (optical fiber), the signal-carrying portion of an optical fiber * Core, the centra ...
and an icy
mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...
. A layer of liquid water may be present at the
core–mantle boundary The core–mantle boundary (CMB) of Earth lies between the planet's silicate mantle and its liquid iron-nickel outer core. This boundary is located at approximately 2,891 km (1,796 miles) depth beneath Earth's surface. The boundary is observed ...
. Its surface, which is relatively dark and slightly red in color, appears to have been shaped by both impacts and
endogenic Endogenous substances and processes are those that originate from within a living system such as an organism, tissue, or cell. In contrast, exogenous substances and processes are those that originate from outside of an organism. For example, e ...
processes. It is covered with numerous
impact crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...
s reaching up to in diameter, but is less heavily cratered than
Oberon Oberon () is a king of the fairies in medieval and Renaissance literature. He is best known as a character in William Shakespeare's play ''A Midsummer Night's Dream'', in which he is King of the Fairies and spouse of Titania, Queen of the Fairi ...
, outermost of the five large moons of Uranus. It may have undergone an early endogenic resurfacing event which obliterated its older, heavily cratered surface. Its surface is cut by a system of enormous
canyon A canyon (from ; archaic British English spelling: ''cañon''), or gorge, is a deep cleft between escarpments or cliffs resulting from weathering and the erosive activity of a river over geologic time scales. Rivers have a natural tendency to cu ...
s and scarps, the result of the expansion of its interior during the later stages of its evolution. Like all major moons of Uranus, Titania probably formed from an
accretion disk An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is typically a star. Friction, uneven irradiance, magnetohydrodynamic effects, and other ...
which surrounded the planet just after its formation.
Infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...
spectroscopy conducted from 2001 to 2005 revealed the presence of water ice as well as frozen
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
on Titania's surface, suggesting it may have a tenuous carbon dioxide
atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A ...
with a surface pressure of about 10 nanopascals (10−13 bar). Measurements during Titania's occultation of a
star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
put an upper limit on the surface pressure of any possible atmosphere at 1–2 mPa (10–20 nbar). The Uranian system has been studied up close only once, by the spacecraft ''
Voyager 2 ''Voyager 2'' is a space probe launched by NASA on August 20, 1977, to study the outer planets and interstellar space beyond the Sun's heliosphere. As a part of the Voyager program, it was launched 16 days before its twin, '' Voyager 1'', ...
'' in January 1986. It took several images of Titania, which allowed mapping of about 40% of its surface.


Discovery and naming

Titania was discovered by William Herschel on January 11, 1787, the same day he discovered Uranus's second largest moon,
Oberon Oberon () is a king of the fairies in medieval and Renaissance literature. He is best known as a character in William Shakespeare's play ''A Midsummer Night's Dream'', in which he is King of the Fairies and spouse of Titania, Queen of the Fairi ...
. He later reported the discoveries of four more satellites, although they were subsequently revealed as spurious. For nearly the next 50 years, Titania and Oberon would not be observed by any instrument other than William Herschel's, although the moon can be seen from
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's sur ...
with a present-day high-end amateur telescope. All of Uranus's moons are named after characters created by
William Shakespeare William Shakespeare ( 26 April 1564 – 23 April 1616) was an English playwright, poet and actor. He is widely regarded as the greatest writer in the English language and the world's pre-eminent dramatist. He is often called England's nation ...
or
Alexander Pope Alexander Pope (21 May 1688 O.S. – 30 May 1744) was an English poet, translator, and satirist of the Enlightenment era who is considered one of the most prominent English poets of the early 18th century. An exponent of Augustan literature, ...
. The name Titania was taken from the Queen of the Fairies in ''
A Midsummer Night's Dream ''A Midsummer Night's Dream'' is a comedy written by William Shakespeare 1595 or 1596. The play is set in Athens, and consists of several subplots that revolve around the marriage of Theseus and Hippolyta. One subplot involves a conflict a ...
''. The names of all four satellites of Uranus then known were suggested by Herschel's son
John John is a common English name and surname: * John (given name) * John (surname) John may also refer to: New Testament Works * Gospel of John, a title often shortened to John * First Epistle of John, often shortened to 1 John * Secon ...
in 1852, at the request of
William Lassell William Lassell (18 June 1799 – 5 October 1880) was an English merchant and astronomer. who had discovered the other two moons, Ariel and Umbriel, the year before. Titania was initially referred to as "the first satellite of Uranus", and in 1848 was given the designation by
William Lassell William Lassell (18 June 1799 – 5 October 1880) was an English merchant and astronomer. although he sometimes used William Herschel's numbering (where Titania and Oberon are II and IV). In 1851 Lassell eventually numbered all four known satellites in order of their distance from the planet by
Roman numerals Roman numerals are a numeral system that originated in ancient Rome and remained the usual way of writing numbers throughout Europe well into the Late Middle Ages. Numbers are written with combinations of letters from the Latin alphabet, ...
, and since then Titania has been designated . Shakespeare's character's name is pronounced , but the moon is often pronounced , by analogy with the familiar chemical element
titanium Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion i ...
. The adjectival form, ''Titanian'', is homonymous with that of Saturn's moon
Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictiona ...
. The name ''Titania'' is ancient Greek for "Daughter of the Titans".


Orbit

Titania orbits Uranus at the distance of about , being the second farthest from the planet among its five major moons after Oberon. Titania's orbit has a small
eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-Centre (geometry), center, in geometry * Eccentricity (g ...
and is
inclined Incline, inclined, inclining, or inclination may refer to: *Grade (slope), the tilt, steepness, or angle from horizontal of a topographic feature (hillside, meadow, etc.) or constructed element (road, railway, field, etc.) *Slope, the tilt, steepn ...
very little relative to the
equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can also ...
of Uranus. Its
orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting pla ...
is around 8.7 days, coincident with its
rotational period The rotation period of a celestial object (e.g., star, gas giant, planet, moon, asteroid) may refer to its sidereal rotation period, i.e. the time that the object takes to complete a single revolution around its axis of rotation relative to the b ...
. In other words, Titania is a
synchronous Synchronization is the coordination of events to operate a system in unison. For example, the conductor of an orchestra keeps the orchestra synchronized or ''in time''. Systems that operate with all parts in synchrony are said to be synchronou ...
or tidally locked satellite, with one face always pointing toward the planet. Titania's orbit lies completely inside the Uranian
magnetosphere In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior d ...
. This is important, because the trailing hemispheres of satellites orbiting inside a magnetosphere are struck by magnetospheric plasma, which co-rotates with the planet. This bombardment may lead to the darkening of the trailing hemispheres, which is actually observed for all Uranian moons except Oberon (see below). Because Uranus orbits the Sun almost on its side, and its moons orbit in the planet's equatorial plane, they (including Titania) are subject to an extreme seasonal cycle. Both northern and southern
poles Poles,, ; singular masculine: ''Polak'', singular feminine: ''Polka'' or Polish people, are a West Slavic nation and ethnic group, who share a common history, culture, the Polish language and are identified with the country of Poland in ...
spend 42 years in a complete darkness, and another 42 years in continuous sunlight, with the sun rising close to the
zenith The zenith (, ) is an imaginary point directly "above" a particular location, on the celestial sphere. "Above" means in the vertical direction ( plumb line) opposite to the gravity direction at that location ( nadir). The zenith is the "high ...
over one of the poles at each
solstice A solstice is an event that occurs when the Sun appears to reach its most northerly or southerly excursion relative to the celestial equator on the celestial sphere. Two solstices occur annually, around June 21 and December 21. In many count ...
. The ''Voyager 2'' flyby coincided with the southern hemisphere's 1986 summer solstice, when nearly the entire southern hemisphere was illuminated. Once every 42 years, when Uranus has an
equinox A solar equinox is a moment in time when the Sun crosses the Earth's equator, which is to say, appears directly above the equator, rather than north or south of the equator. On the day of the equinox, the Sun appears to rise "due east" and se ...
and its equatorial plane intersects the Earth, mutual
occultation An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks ...
s of Uranus's moons become possible. In 2007–2008 a number of such events were observed including two occultations of Titania by Umbriel on August 15 and December 8, 2007.


Composition and internal structure

Titania is the largest and most massive Uranian moon, and the eighth most massive moon in the Solar System. Its density of 1.71 g/cm3, which is much higher than the typical density of Saturn's satellites, indicates that it consists of roughly equal proportions of water ice and dense non-ice components; the latter could be made of rock and
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...
aceous material including heavy
organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
s. The presence of water ice is supported by
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...
spectroscopic Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...
observations made in 2001–2005, which have revealed
crystalline A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...
water ice on the surface of the moon. Water ice
absorption band According to quantum mechanics, atoms and molecules can only hold certain defined quantities of energy, or exist in specific states. When such quanta of electromagnetic radiation are emitted or absorbed by an atom or molecule, energy of the ...
s are slightly stronger on Titania's leading hemisphere than on the trailing hemisphere. This is the opposite of what is observed on Oberon, where the trailing hemisphere exhibits stronger water ice signatures. The cause of this asymmetry is not known, but it may be related to the bombardment by charged particles from the
magnetosphere of Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus (Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars), grandfather of Zeus (Jupiter) and father of Cronu ...
, which is stronger on the trailing hemisphere (due to the plasma's co-rotation). The energetic particles tend to
sputter In physics, sputtering is a phenomenon in which microscopic particles of a solid material are ejected from its surface, after the material is itself bombarded by energetic particles of a plasma or gas. It occurs naturally in outer space, and ca ...
water ice, decompose
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane ...
trapped in ice as
clathrate hydrate Clathrate hydrates, or gas hydrates, clathrates, hydrates, etc., are crystalline water-based solids physically resembling ice, in which small non-polar molecules (typically gases) or polar molecules with large hydrophobic moieties are trapped ...
and darken other organics, leaving a dark, carbon-rich residue behind. Except for water, the only other compound identified on the surface of Titania by infrared spectroscopy is
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
, which is concentrated mainly on the trailing hemisphere. The origin of the carbon dioxide is not completely clear. It might be produced locally from
carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...
s or organic materials under the influence of the solar
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation ...
radiation or energetic charged particles coming from the magnetosphere of Uranus. The latter process would explain the asymmetry in its distribution, because the trailing hemisphere is subject to a more intense magnetospheric influence than the leading hemisphere. Another possible source is the
outgassing Outgassing (sometimes called offgassing, particularly when in reference to indoor air quality) is the release of a gas that was dissolved, trapped, frozen, or absorbed in some material. Outgassing can include sublimation and evaporation (which ...
of the
primordial Primordial may refer to: * Primordial era, an era after the Big Bang. See Chronology of the universe * Primordial sea (a.k.a. primordial ocean, ooze or soup). See Abiogenesis * Primordial nuclide, nuclides, a few radioactive, that formed before t ...
CO2 trapped by water ice in Titania's interior. The escape of CO2 from the interior may be related to the past geological activity on this moon. Titania may be differentiated into a rocky
core Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (manufacturing), used in casting and molding * Core (optical fiber), the signal-carrying portion of an optical fiber * Core, the centra ...
surrounded by an icy
mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...
. If this is the case, the radius of the core is about 66% of the radius of the moon, and its mass is around 58% of the moon's mass—the proportions are dictated by moon's composition. The pressure in the center of Titania is about 0.58  GPa (5.8  kbar). The current state of the icy mantle is unclear. If the ice contains enough ammonia or other
antifreeze An antifreeze is an additive which lowers the freezing point of a water-based liquid. An antifreeze mixture is used to achieve freezing-point depression for cold environments. Common antifreezes also increase the boiling point of the liquid, all ...
, Titania may have a
subsurface ocean Planetary oceanography also called exo-oceanography is the study of oceans on planets and moons other than Earth. Unlike other planetary sciences like astrobiology, astrochemistry and planetary geology, it only began after the discovery of undergr ...
at the core–mantle boundary. The thickness of this ocean, if it exists, is up to and its temperature is around 190  K (close to the water–ammonia
eutectic temperature A eutectic system or eutectic mixture ( ) is a homogeneous mixture that has a melting point lower than those of the constituents. The lowest possible melting point over all of the mixing ratios of the constituents is called the ''eutectic tempe ...
of 176 K). However the present internal structure of Titania depends heavily on its thermal history, which is poorly known.


Surface features

Among Uranus's moons, Titania is intermediate in brightness between the dark Oberon and Umbriel and the bright Ariel and Miranda. Its surface shows a strong
opposition surge The opposition surge (sometimes known as the opposition effect, opposition spike or Seeliger effect) is the brightening of a rough surface, or an object with many particles, when illuminated from directly behind the observer. The term is most wid ...
: its reflectivity decreases from 35% at a phase angle of 0° ( geometrical albedo) to 25% at an angle of about 1°. Titania has a relatively low
Bond albedo The Bond albedo (or ''spheric albedo'' or ''planetary albedo'' or ''bolometric albedo''), named after the American astronomer George Phillips Bond (1825–1865), who originally proposed it, is the fraction of power in the total electromagnetic ra ...
of about 17%. Its surface is generally slightly red in color, but less red than that of
Oberon Oberon () is a king of the fairies in medieval and Renaissance literature. He is best known as a character in William Shakespeare's play ''A Midsummer Night's Dream'', in which he is King of the Fairies and spouse of Titania, Queen of the Fairi ...
. However, fresh impact deposits are bluer, while the smooth plains situated on the leading hemisphere near Ursula crater and along some grabens are somewhat redder. There may be an asymmetry between the leading and trailing hemispheres; the former appears to be redder than the latter by 8%. However, this difference is related to the smooth plains and may be accidental. The reddening of the surfaces probably results from
space weathering Space weathering is the type of weathering that occurs to any object exposed to the harsh environment of outer space. Bodies without atmospheres (including the Moon, Mercury, the asteroids, comets, and most of the moons of other planets) take on ...
caused by bombardment by charged particles and micrometeorites over the age of the
Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...
. However, the color asymmetry of Titania is more likely related to accretion of a reddish material coming from outer parts of the Uranian system, possibly, from
irregular satellite In astronomy, an irregular moon, irregular satellite or irregular natural satellite is a natural satellite following a distant, inclined, and often eccentric and retrograde orbit. They have been captured by their parent planet, unlike regular s ...
s, which would be deposited predominately on the leading hemisphere. Scientists have recognized three classes of geological feature on Titania: craters,
chasm In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben wi ...
ata (
canyon A canyon (from ; archaic British English spelling: ''cañon''), or gorge, is a deep cleft between escarpments or cliffs resulting from weathering and the erosive activity of a river over geologic time scales. Rivers have a natural tendency to cu ...
s) and
rupes Rupes (plural ) is the Latin word for 'cliff'. It is used in planetary geology to refer to escarpments on other worlds. , the IAU has named 62 such features in the Solar System, on Mercury (17), Venus (7), the Moon (8), Mars (23), the asteroids ...
( scarps). The surface of Titania is less heavily cratered than the surfaces of either Oberon or Umbriel, which means that the surface is much younger. The crater diameters reach 326 kilometers for the largest known crater, Gertrude (there can be also a degraded basin of approximately the same size). Some craters (for instance, Ursula and Jessica) are surrounded by bright impact ejecta (
rays Ray may refer to: Fish * Ray (fish), any cartilaginous fish of the superorder Batoidea * Ray (fish fin anatomy), a bony or horny spine on a fin Science and mathematics * Ray (geometry), half of a line proceeding from an initial point * Ray (gra ...
) consisting of relatively fresh ice. All large craters on Titania have flat floors and central peaks. The only exception is Ursula, which has a pit in the center. To the west of Gertrude there is an area with irregular topography, the so-called "unnamed basin", which may be another highly degraded impact basin with the diameter of about . Titania's surface is intersected by a system of enormous faults, or scarps. In some places, two parallel scarps mark depressions in the satellite's crust, forming
graben In geology, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic conte ...
s, which are sometimes called canyons. The most prominent among Titania's canyons is Messina Chasma, which runs for about from the equator almost to the south pole. The grabens on Titania are wide and have a relief of about 2–5 km. The scarps that are not related to canyons are called rupes, such as
Rousillon Rupes Rousillon Rupes is a scarp (''rupes'' is Latin for "cliff") on the surface of the Uranian moon Titania named after "Bertram, count of Rousillon" (an Elisabethan English misspelling for Roussillon) in William Shakespeare's comedy All's Well That ...
near Ursula crater. The regions along some scarps and near Ursula appear smooth at ''Voyager'''s image resolution. These smooth plains were probably resurfaced later in Titania's geological history, after the majority of craters formed. The resurfacing may have been either endogenic in nature, involving the eruption of fluid material from the interior (
cryovolcanism A cryovolcano (sometimes informally called an ice volcano) is a type of volcano that erupts volatiles such as water, ammonia or methane into an extremely cold environment that is at or below their freezing point. The process of formation is known ...
), or, alternatively it may be due to blanking by the impact ejecta from nearby large craters. The grabens are probably the youngest geological features on Titania—they cut all craters and even smooth plains. The geology of Titania was influenced by two competing forces:
impact crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...
formation and endogenic resurfacing. The former acted over the moon's entire history and influenced all surfaces. The latter processes were also global in nature, but active mainly for a period following the moon's formation. They obliterated the original heavily cratered terrain, explaining the relatively low number of impact craters on the moon's present-day surface. Additional episodes of resurfacing may have occurred later and led to the formation of smooth plains. Alternatively smooth plains may be ejecta blankets of the nearby impact craters. The most recent endogenous processes were mainly
tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents ...
in nature and caused the formation of the canyons, which are actually giant cracks in the ice crust. The cracking of the crust was caused by the global expansion of Titania by about 0.7%.


Atmosphere

The presence of carbon dioxide on the surface suggests that Titania may have a tenuous seasonal atmosphere of CO2, much like that of the Jovian moon Callisto. Other gases, like
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
or
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane ...
, are unlikely to be present, because Titania's weak gravity could not prevent them from escaping into space. At the maximum temperature attainable during Titania's
summer solstice The summer solstice, also called the estival solstice or midsummer, occurs when one of Earth's poles has its maximum tilt toward the Sun. It happens twice yearly, once in each hemisphere (Northern and Southern). For that hemisphere, the summer ...
(89 K), the
vapor pressure Vapor pressure (or vapour pressure in English-speaking countries other than the US; see spelling differences) or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed pha ...
of carbon dioxide is about 300 μPa (3 nbar). On September 8, 2001, Titania occulted a bright star ( HIP 106829) with a
visible magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's lig ...
of 7.2; this was an opportunity to both refine Titania's diameter and
ephemeris In astronomy and celestial navigation, an ephemeris (pl. ephemerides; ) is a book with tables that gives the trajectory of naturally occurring astronomical objects as well as artificial satellites in the sky, i.e., the position (and possibly ...
, and to detect any extant atmosphere. The data revealed no atmosphere to a surface pressure of 1–2 mPa (10–20 nbar); if it exists, it would have to be far thinner than that of
Triton Triton commonly refers to: * Triton (mythology), a Greek god * Triton (moon), a satellite of Neptune Triton may also refer to: Biology * Triton cockatoo, a parrot * Triton (gastropod), a group of sea snails * ''Triton'', a synonym of ''Triturus'' ...
or
Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the S ...
. This upper limit is still several times higher than the maximum possible surface pressure of the carbon dioxide, meaning that the measurements place essentially no constraints on parameters of the atmosphere. The peculiar geometry of the Uranian system causes the moons' poles to receive more
solar energy Solar energy is radiant light and heat from the Sun that is harnessed using a range of technologies such as solar power to generate electricity, solar thermal energy (including solar water heating), and solar architecture. It is an essen ...
than their equatorial regions. Because the vapor pressure of CO2 is a steep function of temperature, this may lead to the accumulation of carbon dioxide in the low-latitude regions of Titania, where it can stably exist on high albedo patches and shaded regions of the surface in the form of ice. During the summer, when the polar temperatures reach as high as 85–90 K, carbon dioxide sublimates and migrates to the opposite pole and to the equatorial regions, giving rise to a type of
carbon cycle The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon is the main component of biological compounds as well as a major compon ...
. The accumulated carbon dioxide ice can be removed from cold traps by magnetospheric particles, which sputter it from the surface. Titania is thought to have lost a significant amount of carbon dioxide since its formation 4.6 billion years ago.


Origin and evolution

Titania is thought to have formed from an
accretion disc An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is typically a star. Friction, uneven irradiance, magnetohydrodynamic effects, and other ...
or subnebula; a disc of gas and dust that either existed around Uranus for some time after its formation or was created by the giant impact that most likely gave Uranus its large
obliquity In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orbi ...
. The precise composition of the subnebula is not known; however, the relatively high density of Titania and other Uranian moons compared to the
moons of Saturn The moons of Saturn are numerous and diverse, ranging from tiny moonlets only tens of meters across to enormous Titan, which is larger than the planet Mercury. Saturn has 83 moons with confirmed orbits that are not embedded in its rings—of ...
indicates that it may have been relatively water-poor. Significant amounts of
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
and
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...
may have been present in the form of
carbon monoxide Carbon monoxide ( chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simpl ...
and N2 instead of
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
and methane. The moons that formed in such a subnebula would contain less water ice (with CO and N2 trapped as a clathrate) and more rock, explaining their higher density. Titania's accretion probably lasted for several thousand years. The impacts that accompanied accretion caused heating of the moon's outer layer. The maximum temperature of around was reached at a depth of about . After the end of formation, the subsurface layer cooled, while the interior of Titania heated due to decay of radioactive elements present in its rocks. The cooling near-surface layer contracted, while the interior expanded. This caused strong extensional stresses in the moon's crust leading to cracking. Some of the present-day canyons may be a result of this. The process lasted for about 200 million years, implying that any endogenous activity ceased billions of years ago. The initial accretional heating together with continued decay of radioactive elements were probably strong enough to melt the ice if some antifreeze like ammonia (in the form of ammonia hydrate) or
salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...
was present. Further melting may have led to the separation of ice from rocks and formation of a rocky core surrounded by an icy mantle. A layer of liquid water (ocean) rich in dissolved ammonia may have formed at the core–mantle boundary. The
eutectic temperature A eutectic system or eutectic mixture ( ) is a homogeneous mixture that has a melting point lower than those of the constituents. The lowest possible melting point over all of the mixing ratios of the constituents is called the ''eutectic tempe ...
of this mixture is . If the temperature dropped below this value, the ocean would have subsequently frozen. The freezing of the water would have caused the interior to expand, which may have been responsible for the formation of the majority of the canyons. However, the present knowledge of Titania's geological evolution is quite limited.


Exploration

So far the only close-up images of Titania have been from the ''
Voyager 2 ''Voyager 2'' is a space probe launched by NASA on August 20, 1977, to study the outer planets and interstellar space beyond the Sun's heliosphere. As a part of the Voyager program, it was launched 16 days before its twin, '' Voyager 1'', ...
'' probe, which photographed the moon during its flyby of Uranus in January 1986. Since the closest distance between ''Voyager 2'' and Titania was only , the best images of this moon have a spatial resolution of about 3.4 km (only Miranda and Ariel were imaged with a better resolution). The images cover about 40% of the surface, but only 24% was photographed with the precision required for
geological mapping A geologic map or geological map is a special-purpose map made to show various geological features. Rock units or geologic strata are shown by color or symbols. Bedding planes and structural features such as faults, folds, are shown with s ...
. At the time of the flyby, the southern hemisphere of Titania (like those of the other moons) was pointed towards the
Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
, so the northern (dark) hemisphere could not be studied. No other spacecraft has ever visited the Uranian system or Titania. One possibility, now discarded, was to send '' Cassini'' on from Saturn to Uranus in an extended mission. Another mission concept proposed was the Uranus orbiter and probe concept, evaluated around 2010. Uranus was also examined as part of one trajectory for a precursor interstellar probe concept,
Innovative Interstellar Explorer Innovative Interstellar Explorer was a NASA "Vision Mission" study funded by NASA following a proposal under NRA-03-OSS-01 on 11 September 2003. This study focused on measuring the interstellar medium, the region outside the influence of the ...
. A Uranus orbiter and probe mission architecture was identified as the highest priority for a NASA Flagship mission by the 2023-2032
Planetary Science Decadal Survey The Planetary Science Decadal Survey is a publication of the United States National Research Council produced for NASA and other United States Government Agencies such as the National Science Foundation.National Academy of Sciences, National Acade ...
. The science questions motivating this prioritization include questions about the Uranian satellites' bulk properties, internal structure, and geologic history. A Uranus orbiter was listed as the third priority for a NASA Flagship mission by the 2013-2022
Planetary Science Decadal Survey The Planetary Science Decadal Survey is a publication of the United States National Research Council produced for NASA and other United States Government Agencies such as the National Science Foundation.National Academy of Sciences, National Acade ...
, and conceptual designs for such a mission are currently being analyzed.Stephen Clar
"Uranus, Neptune in NASA’s sights for new robotic mission"
''Spaceflight Now,'' August 25, 2015


See also

* Titania in fiction *
List of natural satellites The Solar System's planets, and its most likely dwarf planets, are known to be orbited by at least 221 natural satellites, or moons. At least 20 of them are large enough to be gravitationally rounded; of these, all are covered by a crust of ...


Notes


References


External links

*
NASA archive of publicly released Titania images
* *

(includin
labelledmaps
of Titania) at ''Views of the Solar System''
Titania nomenclature
from th
USGS Planetary Nomenclature web site
{{Featured article 17870111 Discoveries by William Herschel Things named after Shakespearean works Moons with a prograde orbit