Titania (moon)

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Titania
Titania (moon) color, edited.jpg
Voyager 2 image of Titania's southern hemisphere [caption 1]
Discovery
Discovered by William Herschel
Discovery dateJanuary 11, 1787 [1]
Designations
Pronunciation /tɪˈtniə, t-/ [lower-alpha 1]
Uranus III
Adjectives Titanian
Orbital characteristics
435910 km [3]
Eccentricity 0.0011 [3]
8.706234 d [3]
Average orbital speed
3.64 km/s [lower-alpha 2]
Inclination 0.340° (to Uranus's equator) [3]
Satellite of Uranus
Physical characteristics
Mean radius
788.4±0.6 km (0.1235 Earths) [4]
7820000 km2 [lower-alpha 3]
Volume 2065000000 km3 [lower-alpha 4]
Mass (3.527±0.09)×1021 kg (5.908×10−4 Earths) [5]
Mean density
1.711±0.005 g/cm³ [4]
0.379 m/s² [lower-alpha 5]
0.773 km/s [lower-alpha 6]
presumed synchronous [6]
Albedo
  • 0.35 (geometrical)
  • 0.17 (Bond) [7]
Surface temp. minmeanmax
solstice [4] 60 K70 ± 7  K 89 K
13.9 [8]
Atmosphere
Surface pressure
<1–2  mPa (10–20  nbar)
Composition by volume

Titania is the largest of the moons of Uranus and the eighth largest moon in the Solar System at a diameter of 1,578 kilometres (981 mi). Discovered by William Herschel in 1787, Titania is named after the queen of the fairies in Shakespeare's A Midsummer Night's Dream . Its orbit lies inside Uranus's magnetosphere.

Moons of Uranus The natural satellites of the planet Uranus

Uranus, the seventh planet of the Solar System, has 27 known moons, all of which are named after characters from the works of William Shakespeare and Alexander Pope. Uranus's moons are divided into three groups: thirteen inner moons, five major moons, and nine irregular moons. The inner moons are small dark bodies that share common properties and origins with Uranus's rings. The five major moons are massive enough to have reached hydrostatic equilibrium, and four of them show signs of internally driven processes such as canyon formation and volcanism on their surfaces. The largest of these five, Titania, is 1,578 km in diameter and the eighth-largest moon in the Solar System, and about one-twentieth the mass the Earth's Moon. The orbits of the regular moons are nearly coplanar with Uranus's equator, which is tilted 97.77° to its orbit. Uranus's irregular moons have elliptical and strongly inclined orbits at large distances from the planet.

Solar System planetary system of the Sun

The Solar System is the gravitationally bound planetary system of the Sun and the objects that orbit it, either directly or indirectly. Of the objects that orbit the Sun directly, the largest are the eight planets, with the remainder being smaller objects, such as the five dwarf planets and small Solar System bodies. Of the objects that orbit the Sun indirectly—the moons—two are larger than the smallest planet, Mercury.

William Herschel 18th and 19th-century German-born British astronomer and composer

Frederick William Herschel, was a German-born British astronomer, composer and brother of fellow astronomer Caroline Herschel, with whom he worked. Born in the Electorate of Hanover, Herschel followed his father into the Military Band of Hanover, before migrating to Great Britain in 1757 at the age of nineteen.

Contents

Titania consists of approximately equal amounts of ice and rock, and is probably differentiated into a rocky core and an icy mantle. A layer of liquid water may be present at the core–mantle boundary. The surface of Titania, which is relatively dark and slightly red in color, appears to have been shaped by both impacts and endogenic processes. It is covered with numerous impact craters reaching up to 326 kilometres (203 mi) in diameter, but is less heavily cratered than Oberon, outermost of the five large moons of Uranus. Titania probably underwent an early endogenic resurfacing event which obliterated its older, heavily cratered surface. Titania's surface is cut by a system of enormous canyons 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 which surrounded the planet just after its formation.

Rock (geology) A naturally occurring solid aggregate of one or more minerals or mineraloids

Rock or stone is a natural substance, a solid aggregate of one or more minerals or mineraloids. For example, granite, a common rock, is a combination of the minerals quartz, feldspar and biotite. The Earth's outer solid layer, the lithosphere, is made of rock.

A mantle is a layer inside a planetary body bounded below by a core and above by a crust. Mantles are made of rock or ices, and are generally the largest and most massive layer of the planetary body. Mantles are characteristic of planetary bodies that have undergone differentiation by density. All terrestrial planets, a number of asteroids, and some planetary moons have mantles.

Core–mantle boundary Discontinuity where the bottom of the planets mantle meets the outer layer of the core

The core–mantle boundary of the Earth lies between the planet's silicate mantle and its liquid iron-nickel outer core. This boundary is located at approximately 2891 km (1796 mi) depth beneath the Earth's surface. The boundary is observed via the discontinuity in seismic wave velocities at that depth due to the differences between the acoustic impedances of the solid mantle and the molten outer core. P-wave velocities are much slower in the outer core than in the deep mantle while S-waves do not exist at all in the liquid portion of the core. Recent evidence suggests a distinct boundary layer directly above the CMB possibly made of a novel phase of the basic perovskite mineralogy of the deep mantle named post-perovskite. Seismic tomography studies have shown significant irregularities within the boundary zone and appear to be dominated by the African and Pacific large low-shear-velocity provinces (LLSVPs).

Infrared spectroscopy conducted from 2001 to 2005 revealed the presence of water ice as well as frozen carbon dioxide on the surface of Titania, which in turn suggested that the moon may have a tenuous carbon dioxide atmosphere with a surface pressure of about 10 nanopascals (10−13 bar). Measurements during Titania's occultation of a star put an upper limit on the surface pressure of any possible atmosphere at 1–2 mPa (10–20 nbar).

Infrared electromagnetic radiation with longer wavelengths than those of visible light

Infrared radiation (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with longer wavelengths than those of visible light, and is therefore generally invisible to the human eye, although IR at wavelengths up to 1050 nanometers (nm)s from specially pulsed lasers can be seen by humans under certain conditions. IR wavelengths extend from the nominal red edge of the visible spectrum at 700 nanometers, to 1 millimeter (300 GHz). Most of the thermal radiation emitted by objects near room temperature is infrared. As with all EMR, IR carries radiant energy and behaves both like a wave and like its quantum particle, the photon.

Ice water frozen into the solid state

Ice is water frozen into a solid state. Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaque bluish-white color.

Carbon dioxide chemical compound

Carbon dioxide (chemical formula CO2) is a colorless gas with a density about 60% higher than that of dry air. Carbon dioxide consists of a carbon atom covalently double bonded to two oxygen atoms. It occurs naturally in Earth's atmosphere as a trace gas. The current concentration is about 0.04% (410 ppm) by volume, having risen from pre-industrial levels of 280 ppm. Natural sources include volcanoes, hot springs and geysers, and it is freed from carbonate rocks by dissolution in water and acids. Because carbon dioxide is soluble in water, it occurs naturally in groundwater, rivers and lakes, ice caps, glaciers and seawater. It is present in deposits of petroleum and natural gas. Carbon dioxide is odorless at normally encountered concentrations. However, at high concentrations, it has a sharp and acidic odor.

The Uranian system has been studied up close only once, by the spacecraft Voyager 2 in January 1986. It took several images of Titania, which allowed mapping of about 40% of its surface.

<i>Voyager 2</i> Space probe and the second-farthest man-made object from Earth

Voyager 2 is a space probe launched by NASA on August 20, 1977, to study the outer planets. Part of the Voyager program, it was launched 16 days before its twin, Voyager 1, on a trajectory that took longer to reach Jupiter and Saturn but enabled further encounters with Uranus and Neptune. It is the only spacecraft to have visited either of these two ice giant planets.

History

Titania was discovered by William Herschel on January 11, 1787, the same day he discovered Uranus's second largest moon, Oberon. [1] [9] He later reported the discoveries of four more satellites, [10] although they were subsequently revealed as spurious. [11] For nearly fifty years following their discovery, Titania and Oberon would not be observed by any instrument other than William Herschel's, [12] although the moon can be seen from Earth with a present-day high-end amateur telescope. [8]

Oberon (moon) moon of Uranus

Oberon, also designated Uranus IV, is the outermost major moon of the planet Uranus. It is the second-largest and second most massive of the Uranian moons, and the ninth most massive moon in the Solar System. Discovered by William Herschel in 1787, Oberon is named after the mythical king of the fairies who appears as a character in Shakespeare's A Midsummer Night's Dream. Its orbit lies partially outside Uranus's magnetosphere.

Earth Third planet from the Sun in the Solar System

Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space, especially the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in 365.26 days, a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times.

Size comparison of Earth, the Moon, and Titania. Titania Earth Moon Comparison.png
Size comparison of Earth, the Moon, and Titania.

All of Uranus's moons are named after characters created by William Shakespeare or Alexander Pope. The name Titania was taken from the Queen of the Fairies in A Midsummer Night's Dream . [13] The names of all four satellites of Uranus then known were suggested by Herschel's son John in 1852, at the request of William Lassell, [14] who had discovered the other two moons, Ariel and Umbriel, the year before. [15]

William Shakespeare English playwright and poet

William Shakespeare was an English poet, playwright and actor, widely regarded as the greatest writer in the English language and the world's greatest dramatist. He is often called England's national poet and the "Bard of Avon". His extant works, including collaborations, consist of approximately 39 plays, 154 sonnets, two long narrative poems, and a few other verses, some of uncertain authorship. His plays have been translated into every major living language and are performed more often than those of any other playwright.

Alexander Pope English poet

Alexander Pope was an 18th-century English poet. He is best known for his satirical verse, including Essay on Criticism, The Rape of the Lock and The Dunciad, and for his translation of Homer. He is the second-most frequently quoted writer in The Oxford Dictionary of Quotations after Shakespeare.

<i>A Midsummer Nights Dream</i> play by William Shakespeare

A Midsummer Night's Dream is a comedy written by William Shakespeare in 1595/96. It portrays the events surrounding the marriage of Theseus, the Duke of Athens, to Hippolyta. These include the adventures of four young Athenian lovers and a group of six amateur actors who are controlled and manipulated by the fairies who inhabit the forest in which most of the play is set. The play is one of Shakespeare's most popular works for the stage and is widely performed across the world.

Titania was initially referred to as "the first satellite of Uranus", and in 1848 was given the designation Uranus I by William Lassell, [16] although he sometimes used William Herschel's numbering (where Titania and Oberon are II and IV). [17] In 1851 Lassell eventually numbered all four known satellites in order of their distance from the planet by Roman numerals, and since then Titania has been designated Uranus III. [18]

Shakespeare's character's name is pronounced /tɪˈtnjə/ , but the moon is often pronounced /tˈtniə/ , by analogy with the familiar chemical element titanium. [2] The adjectival form, Titanian, is homonymous with that of Saturn's moon Titan. The name Titania is ancient Greek in origin, meaning "Daughter of the Titans".

Orbit

Titania orbits Uranus at the distance of about 436,000 kilometres (271,000 mi), being the second farthest from the planet among its five major moons. [lower-alpha 7] Titania's orbit has a small eccentricity and is inclined very little relative to the equator of Uranus. [3] Its orbital period is around 8.7 days, coincident with its rotational period. In other words, Titania is a synchronous or tidally locked satellite, with one face always pointing toward the planet. [6]

Titania's orbit lies completely inside the Uranian magnetosphere. [19] This is important, because the trailing hemispheres of satellites orbiting inside a magnetosphere are struck by magnetospheric plasma, which co-rotates with the planet. [20] This bombardment may lead to the darkening of the trailing hemispheres, which is actually observed for all Uranian moons except Oberon (see below). [19]

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 spend 42 years in a complete darkness, and another 42 years in continuous sunlight, with the sun rising close to the zenith over one of the poles at each solstice. [19] 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 and its equatorial plane intersects the Earth, mutual occultations 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. [21] [22]

Composition and internal structure

Voyager 2's highest-resolution image of Titania shows moderately cratered plains, enormous rifts and long scarps. Near the bottom, a region of smoother plains including the crater Ursula is split by the graben Belmont Chasma. PIA00039 Titania.jpg
Voyager 2's highest-resolution image of Titania shows moderately cratered plains, enormous rifts and long scarps. Near the bottom, a region of smoother plains including the crater Ursula is split by the graben Belmont Chasma.

Titania is the largest and most massive Uranian moon, and the eighth most massive moon in the Solar System. [lower-alpha 8] Its density of 1.71 g/cm³, [5] 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; [24] the latter could be made of rock and carbonaceous material including heavy organic compounds. [6] The presence of water ice is supported by infrared spectroscopic observations made in 2001–2005, which have revealed crystalline water ice on the surface of the moon. [19] Water ice absorption bands 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. [19] The cause of this asymmetry is not known, but it may be related to the bombardment by charged particles from the magnetosphere of Uranus, which is stronger on the trailing hemisphere (due to the plasma's co-rotation). [19] The energetic particles tend to sputter water ice, decompose methane trapped in ice as clathrate hydrate and darken other organics, leaving a dark, carbon-rich residue behind. [19]

Except for water, the only other compound identified on the surface of Titania by infrared spectroscopy is carbon dioxide, which is concentrated mainly on the trailing hemisphere. [19] The origin of the carbon dioxide is not completely clear. It might be produced locally from carbonates or organic materials under the influence of the solar ultraviolet 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 of the primordial 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. [19]

Titania may be differentiated into a rocky core surrounded by an icy mantle. [24] If this is the case, the radius of the core 520 kilometres (320 mi) 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). [24] The current state of the icy mantle is unclear. If the ice contains enough ammonia or other antifreeze, Titania may have a subsurface ocean at the core–mantle boundary. The thickness of this ocean, if it exists, is up to 50 kilometres (31 mi) and its temperature is around 190  K. [24] However the present internal structure of Titania depends heavily on its thermal history, which is poorly known.

Surface features

Titania with surface features labeled. The south pole is situated close to the unidentified bright crater below and left of the crater Jessica. Titania (moon) labeled.jpg
Titania with surface features labeled. The south pole is situated close to the unidentified bright crater below and left of the crater Jessica.

Among Uranus's moons, Titania is intermediate in brightness between the dark Oberon and Umbriel and the bright Ariel and Miranda. [7] Its surface shows a strong opposition surge: 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 of about 17%. [7] Its surface is generally slightly red in color, but less red than that of Oberon. [25] 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. [25] [26] There may be an asymmetry between the leading and trailing hemispheres; [27] the former appears to be redder than the latter by 8%. [lower-alpha 9] However, this difference is related to the smooth plains and may be accidental. [25] The reddening of the surfaces probably results from space weathering caused by bombardment by charged particles and micrometeorites over the age of the Solar System. [25] 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 satellites, which would be deposited predominately on the leading hemisphere. [27]

Scientists have recognized three classes of geological feature on Titania: craters, chasmata (canyons) and rupes (scarps). [28] The surface of Titania is less heavily cratered than the surfaces of either Oberon or Umbriel, which means that the surface is much younger. [26] The crater diameters reach 326 kilometers for the largest known crater, Gertrude [29] (there can be also a degraded basin of approximately the same size). [26] Some craters (for instance, Ursula and Jessica) are surrounded by bright impact ejecta (rays) consisting of relatively fresh ice. [6] All large craters on Titania have flat floors and central peaks. The only exception is Ursula, which has a pit in the center. [26] 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 330 kilometres (210 mi). [26]

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, [6] forming grabens, which are sometimes called canyons. [30] The most prominent among Titania's canyons is Messina Chasma, which runs for about 1,500 kilometres (930 mi) from the equator almost to the south pole. [28] The grabens on Titania are 20–50 kilometres (12–31 mi) wide and have a relief of about 2–5 km. [6] The scarps that are not related to canyons are called rupes, such as Rousillon Rupes near Ursula crater. [28] 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), or, alternatively it may be due to blanking by the impact ejecta from nearby large craters. [26] The grabens are probably the youngest geological features on Titania—they cut all craters and even smooth plains. [30]

The geology of Titania was influenced by two competing forces: impact crater formation and endogenic resurfacing. [30] 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. [26] They obliterated the original heavily cratered terrain, explaining the relatively low number of impact craters on the moon's present-day surface. [6] Additional episodes of resurfacing may have occurred later and led to the formation of smooth plains. [6] Alternatively smooth plains may be ejecta blankets of the nearby impact craters. [30] The most recent endogenous processes were mainly tectonic in nature and caused the formation of the canyons, which are actually giant cracks in the ice crust. [30] The cracking of the crust was caused by the global expansion of Titania by about 0.7%. [30]

Messina Chasma--a large canyon on Titania Messina Chasma.jpg
Messina Chasma—a large canyon on Titania
Named surface features on Titania [28]
FeatureNamed afterTypeLength (diameter), kmCoordinates
Belmont Chasma Belmont, Italy ( The Merchant of Venice ) Chasma 238 8°30′S32°36′E / 8.5°S 32.6°E / -8.5; 32.6
Messina Chasmata Messina, Italy ( Much Ado About Nothing )1,492 33°18′S335°00′E / 33.3°S 335°E / -33.3; 335
Rousillon Rupes Roussillon, France ( All's Well That Ends Well ) Rupes 402 14°42′S23°30′E / 14.7°S 23.5°E / -14.7; 23.5
AdrianaAdriana ( The Comedy of Errors ) Crater 50 20°06′S3°54′E / 20.1°S 3.9°E / -20.1; 3.9
BonaBona ( Henry VI, Part 3 )51 55°48′S351°12′E / 55.8°S 351.2°E / -55.8; 351.2
Calphurnia Calpurnia Pisonis ( Julius Caesar )100 42°24′S291°24′E / 42.4°S 291.4°E / -42.4; 291.4 (Calphurnia crater)
Elinor Eleanor of Aquitaine ( The Life and Death of King John )74 44°48′S333°36′E / 44.8°S 333.6°E / -44.8; 333.6
Gertrude Gertrude ( Hamlet )326 15°48′S287°06′E / 15.8°S 287.1°E / -15.8; 287.1
ImogenImogen (Cymbeline)28 23°48′S321°12′E / 23.8°S 321.2°E / -23.8; 321.2
IrasIras ( Antony and Cleopatra )33 19°12′S338°48′E / 19.2°S 338.8°E / -19.2; 338.8
JessicaJessica (The Merchant of Venice)64 55°18′S285°54′E / 55.3°S 285.9°E / -55.3; 285.9
KatherineKatherine ( Henry VIII )75 51°12′S331°54′E / 51.2°S 331.9°E / -51.2; 331.9
LucettaLucetta ( The Two Gentlemen of Verona )58 14°42′S277°06′E / 14.7°S 277.1°E / -14.7; 277.1
MarinaMarina ( Pericles, Prince of Tyre )40 15°30′S316°00′E / 15.5°S 316°E / -15.5; 316
MopsaMopsa ( The Winter's Tale )101 11°54′S302°12′E / 11.9°S 302.2°E / -11.9; 302.2
PhryniaPhrynia ( Timon of Athens )35 24°18′S309°12′E / 24.3°S 309.2°E / -24.3; 309.2
Ursula Ursula (Much Ado About Nothing)135 12°24′S45°12′E / 12.4°S 45.2°E / -12.4; 45.2
ValeriaValeria ( Coriolanus )59 34°30′S4°12′E / 34.5°S 4.2°E / -34.5; 4.2
Surface features on Titania are named for female characters from Shakespeare's works. [31]

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. [lower-alpha 10] [4] Other gases, like nitrogen or 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 (89 K), the vapor pressure of carbon dioxide is about 300 μPa (3 nbar). [4]

On September 8, 2001, Titania occulted a bright star (HIP106829) with a visible magnitude of 7.2; this was an opportunity to both refine Titania's diameter and ephemeris, 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 or Pluto. [4] 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. [4]

The peculiar geometry of the Uranian system causes the moons' poles to receive more solar energy than their equatorial regions. [19] Because the vapor pressure of CO2 is a steep function of temperature, [4] 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, [4] [19] carbon dioxide sublimates and migrates to the opposite pole and to the equatorial regions, giving rise to a type of carbon cycle. 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. [19]

Origin and evolution

Titania is thought to have formed from an accretion disc 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. [32] 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 indicates that it may have been relatively water-poor. [lower-alpha 11] [6] Significant amounts of nitrogen and carbon may have been present in the form of carbon monoxide and N2 instead of ammonia and methane. [32] 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. [6]

Titania's accretion probably lasted for several thousand years. [32] The impacts that accompanied accretion caused heating of the moon's outer layer. [33] The maximum temperature of around 250 K (−23 °C) was reached at a depth of about 60 kilometres (37 mi). [33] 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. [6] 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, [34] implying that any endogenous activity ceased billions of years ago. [6]

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 was present. [33] 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. [24] The eutectic temperature of this mixture is 176 K (−97 °C). [24] 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. [26] 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 probe, which photographed the moon during its flyby of Uranus in January 1986. Since the closest distance between Voyager 2 and Titania was only 365,200 km (226,900 mi), [35] 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). [26] The images cover about 40% of the surface, but only 24% was photographed with the precision required for geological mapping. At the time of the flyby, the southern hemisphere of Titania (like those of the other moons) was pointed towards the Sun, so the northern (dark) hemisphere could not be studied. [6]

No other spacecraft has ever visited the Uranian system or Titania, and no mission is currently planned. 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.

A Uranus orbiter [36] was listed as the third priority for a NASA Flagship mission by the NASA Planetary Science Decadal Survey, and conceptual designs for such a mission are currently being analyzed. [37]

See also

Notes

  1. Along the terminator are visible the moon's largest known impact crater, Gertrude, at upper right and several enormous canyon-like grabens (the Messina Chasmata above, Belmont Chasma near bottom) at lower right.
  1. ti-TAY-nee-ə, ty-. [2] The former pronunciation is distinct from the adjectival form of Saturn's moon Titan.
  2. Calculated on the basis of other parameters.
  3. Surface area derived from the radius r : 4πr².
  4. Volume v derived from the radius r : 4πr³/3.
  5. Surface gravity derived from the mass m, the gravitational constant G and the radius r : Gm/r².
  6. Escape velocity derived from the mass m, the gravitational constant G and the radius r : 2Gm/r.
  7. The five major moons are Miranda, Ariel, Umbriel, Titania and Oberon.
  8. The seven moons more massive than Titania are Ganymede, Titan, Callisto, Io, Earth's Moon, Europa, and Triton. [23]
  9. The color is determined by the ratio of albedos viewed through the green (0.52–0.59 μm) and violet (0.38–0.45 μm) Voyager filters. [25] [27]
  10. The partial pressure of CO2 on the surface of Callisto is about 10 nPa (10 pbar).
  11. For instance, Tethys, a Saturnian moon, has the density of 0.97 g/cm³, which implies it contains more than 90% of water. [19]

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Nereid is the third-largest moon of Neptune. It has a highly eccentric orbit. It was the second moon of Neptune to be discovered, by Gerard Kuiper in 1949.

Umbriel (moon) moon of Uranus

Umbriel is a moon of Uranus discovered on October 24, 1851, by William Lassell. It was discovered at the same time as Ariel and named after a character in Alexander Pope's poem The Rape of the Lock. Umbriel consists mainly of ice with a substantial fraction of rock, and may be differentiated into a rocky core and an icy mantle. The surface is the darkest among Uranian moons, and appears to have been shaped primarily by impacts. However, the presence of canyons suggests early endogenic processes, and the moon may have undergone an early endogenically driven resurfacing event that obliterated its older surface.

Triton (moon) largest moon of Neptune

Triton is the largest natural satellite of the planet Neptune, and the first Neptunian moon to be discovered. The discovery was made on October 10, 1846, by English astronomer William Lassell. It is the only large moon in the Solar System with a retrograde orbit, an orbit in the direction opposite to its planet's rotation. At 2,710 kilometres (1,680 mi) in diameter, it is the seventh-largest moon in the Solar System, and the only moon of Neptune massive enough to be in hydrostatic equilibrium. Because of its retrograde orbit and composition similar to Pluto's, Triton is thought to have been a dwarf planet captured from the Kuiper belt. It has a surface of mostly frozen nitrogen, a mostly water-ice crust, an icy mantle and a substantial core of rock and metal. The core makes up two-thirds of its total mass. The mean density is 2.061 g/cm3, reflecting a composition of approximately 15–35% water ice.

Uranus Seventh planet from the Sun in the Solar System

Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. Uranus is similar in composition to Neptune, and both have bulk chemical compositions which differ from that of the larger gas giants Jupiter and Saturn. For this reason, scientists often classify Uranus and Neptune as "ice giants" to distinguish them from the gas giants. Uranus' atmosphere is similar to Jupiter's and Saturn's in its primary composition of hydrogen and helium, but it contains more "ices" such as water, ammonia, and methane, along with traces of other hydrocarbons. It is the coldest planetary atmosphere in the Solar System, with a minimum temperature of 49 K, and has a complex, layered cloud structure with water thought to make up the lowest clouds and methane the uppermost layer of clouds. The interior of Uranus is mainly composed of ices and rock.

Puck (moon) moon of Uranus

Puck is an inner moon of Uranus. It was discovered in December 1985 by the Voyager 2 spacecraft. The name Puck follows the convention of naming Uranus's moons after characters from Shakespeare. The orbit of Puck lies between the rings of Uranus and the first of Uranus's large moons, Miranda. Puck is approximately spherical in shape and has diameter of about 162 km. It has a dark, heavily cratered surface, which shows spectral signs of water ice.

Rhea (moon) moon of Saturn

Rhea is the second-largest moon of Saturn and the ninth-largest moon in the Solar System. It is the second smallest body in the Solar System for which precise measurements have confirmed a shape consistent with hydrostatic equilibrium, after dwarf planet Ceres. It was discovered in 1672 by Giovanni Domenico Cassini.

Tethys (moon) moon of Saturn

Tethys is a mid-sized moon of Saturn about 1,060 km (660 mi) across. It was discovered by G. D. Cassini in 1684 and is named after the titan Tethys of Greek mythology.

Hyperion (moon) moon of Saturn

Hyperion, also known as Saturn VII (7), is a moon of Saturn discovered by William Cranch Bond, George Phillips Bond and William Lassell in 1848. It is distinguished by its irregular shape, its chaotic rotation, and its unexplained sponge-like appearance. It was the first non-round moon to be discovered.

Ariel (moon) fourth-largest moon of Uranus

Ariel is the fourth-largest of the 27 known moons of Uranus. Ariel orbits and rotates in the equatorial plane of Uranus, which is almost perpendicular to the orbit of Uranus and so has an extreme seasonal cycle.

Wunda (crater) crater on the surface of Uranus moon Umbriel

Wunda is a large crater on the surface of Uranus' moon Umbriel. It is 131 km in diameter and is located near the equator of Umbriel. The crater is named after Wunda, a dark spirit of Australian aboriginal mythology.

The naming of moons has been the responsibility of the International Astronomical Union's committee for Planetary System Nomenclature since 1973. That committee is known today as the Working Group for Planetary System Nomenclature (WGPSN).

Exploration of Uranus

The exploration of Uranus has, to date, been solely through telescopes and NASA's Voyager 2 spacecraft, which made its closest approach to Uranus on January 24, 1986. Voyager 2 discovered 10 moons, studied the planet's cold atmosphere, and examined its ring system, discovering two new rings. It also imaged Uranus' five large moons, revealing that their surfaces are covered with impact craters and canyons.

Mommur Chasma chasma on Oberon

Mommur Chasma is the largest 'canyon' on the known part of the surface of Uranus' moon Oberon. This feature probably formed during crustal extension at the early stages of moon's evolution, when the interior of Oberon expanded and its ice crust cracked as a result. The canyon is an example of graben or scarp produced by normal fault(s). The chasma was first imaged by Voyager 2 spacecraft in January 1986.

Messina Chasmata chasma on Titania

The Messina Chasmata are the largest canyon or system of canyons on the surface of the Uranian moon Titania, named after a location in William Shakespeare's comedy Much Ado About Nothing. The 1492 km long feature includes two normal faults running NW–SE, which bound a down-dropped crustal block forming a structure called a graben. The graben cuts impact craters, which probably means that it was formed at a relatively late stage of the moon's evolution, when the interior of Titania expanded and its ice crust cracked as a result. The Messina Chasmata have only a few superimposed craters, which also implies being relatively young. The feature was first imaged by Voyager 2 in January 1986.

Ursula (crater) crater on Uranuss moon Titania

Ursula is a large crater on Uranus's moon Titania. It is about 135 km across, and is cut by Belmont Chasma. It is named after Hero's attendant in William Shakespeare's comedy Much Ado About Nothing.

Vuver (crater) crater on the surface of Uranus moon Umbriel

Vuver is a crater on the surface of Uranus' moon Umbriel. It is estimated to be 98 km in diameter. The longitude and latitude of its center are 311.6° and −4.7°, respectively.

Rousillon Rupes rupes on Titania

Rousillon Rupes is a scarp on the surface of the Uranian moon Titania named after "Bertram, count of Rousillon" in William Shakespeare's comedy All's Well That Ends Well. The 402 km long feature is a normal fault situated near the equator and running perpendicular to it. The scarp cuts impact craters, which probably means that it was formed at a relatively late stage of moon's evolution, when the interior of Titania expanded and its ice crust cracked as a result. Rousillon Rupes has only few crater superimposed on it, which also implies its relatively young age. The scarp was first imaged by Voyager 2 spacecraft in January 1986.

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