Titania （Titania / tɪˈtɑːniə /），Also known as Uranus III, it isUranusLargest satellite andsolar systemThe eighth largest satellite.The diameter is 1578 km (981 miles).1787William Herschel It was found that the third day of TianweiShakespeare《Midsummer Night's Dream》The fairy queen was named.Its orbit is within Uranus's magnetosphere.
Triton is composed of about the same amount of ice and rock, and may be differentiated into rock core and icemantleThe core mantle boundary may have a layer of liquid water ocean.The surface of Triton is relatively dark and reddish, which seems to be shaped by impact and endogenous tectonic processes.It covers countlessImpact craterWith a diameter of 326 kilometers (203 miles), but the impact crater is not as large as the outermost of Uranus's five major moonsTianwei IVSerious.Triton may have experienced an early endogenous surface regeneration event, covering its older, pitted surface.tremendouscanyonandSteep cliffThe system cut the surface of Triton, which is the result of its internal expansion in the later development.Like all the major moons of Uranus, Triton may have been formed by UranusAccretion diskAccumulated.
From 2001 to 2005infraredSpectral studies reveal that there are water ice and carbon dioxide dry ice on the surface of Triton, which may contain weakcarbon dioxideAtmosphere, the surface pressure is about 10 kPa (10 − 13 bar).Titania OccultationThe measured value during the period is 1 – 2 mPa (10 – 20 nbar), and the surface pressure of any possible atmosphere is set to the upper limit.
have onlyVoyager 2In January 1986, a close study of the Uranus system was carried out. It took several images of Triton and drew about 40% of the surface.
On January 11, 1787, William Herschel discovered Triton, and on the same day he also discovered the second largest moon of Uranus, Triton.[1-2]He later claimed to have discovered four more Uranus moons,[3]But later astronomers found that the statement was wrong.[4]Although people can observe Triton and Triton on the earth with modern amateur telescopes, in the fifty years after William Herschel announced the discovery of these two satellites, no astronomical observation instrument on the earth could observe them again.[5]
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The English names of all the satellites of Uranus are named after the characters created by William Shakespeare or Alexander Pope.The English name Titania is taken from the Midsummer Night Dream[6]The goblin queen in.The names of all four Uranus moons were proposed by John Herschel, the son of William Herschel, in 1852 at the request of William Russell,[7]William Lassell The other two moons of Uranus were discovered the year before,Tianwei I(Ariel) andEnceladus（Umbriel）。[8]
Triton was initially called "the first satellite of Uranus" and was named "Uranus I" by William Russell in 1848.[9]However, he still sometimes uses the name given by William Herschel (he calls Triton and Triton "Uranus II" and "UranVus I" respectively).[10]In 1851, Russell adoptedRoman numeralsIt was named after all the known Uranus moons at that time, and from then on Triton was called "Uranus III".[11]The name of Shakespeare's character is pronounced/t 618ˈ te 618ɪ nj ə/, but Tianwei is usually pronounced/ta 618ˈ te ɪ ni ə/, similar to familiar chemical elementstitanium。[12]The adjective form is homophone with Titan.Titania's name originates fromancient Greek, meaning Titan's daughter.
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The orbit of Triton around Uranus is about 436000 kilometers (271000 miles), which is the second largest of the five major satellites of Uranus.ApostoidEccentricityandRail inclination(relative to the equator of Uranus) relatively small.[13]The orbital revolution period of Triton is about 8.7 days, which is exactly the same as its rotation period.In other words, Triton is a synchronous rotation satellite or tide locked satellite, with one side always facing Uranus.[14]
Triton's orbit is completely located on UranusMagnetosphereInside.[15]This is important because satellites operating inside the magnetosphere are bombarded by the magnetospheric plasma that rotates with the planet, away from the orbiting hemisphere.[16]This bombardment may cause the back hemisphere to darken, which has actually been observed on all Uranus satellites except Triton.[15]
Since Uranus almost lies around the sun, and its satellites revolve in the equatorial plane of the planet, they (including Triton) will experience an extreme seasonal cycle.The Arctic and Antarctic will spend 42 years in complete darkness and 42 years in continuous sunshine. Every winter solstice, the sun rises near the pole.[15]The Voyager 2 flyby coincided with the 1986 summer solstice in the southern hemisphere, almost illuminating the entire southern hemisphere.Uranus appears at the vernal equinox every 42 years, when its equatorial plane intersects the earth, and its satellites may appear to interact with each othereclipse。In 2007 – 2008, many such events were observed, including the eclipse of Triton by Enceladus on August 15 and December 8, 2007.[17-18]
Material composition and internal structure
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Triton is the largest satellite of Uranus in size and mass, and also the eighth largest satellite in the solar system.The density of Triton is 1.71g/cm ³,[19]It is much higher than the typical density of Saturn's satellite, indicating that it is composed of approximately equal proportion of water ice and dense non ice components;[20]The latter can be rocks and carbon based materials including heavier organic compounds.[21]The observation of infrared spectra from 2001 to 2005 showed that there was crystalline water ice on the surface of its satellite.[15]Water ice in the hemisphere of Triton orbitAbsorption bandSlightly stronger than the contraorbital hemisphere.This is contrary to the results observed in Triton, whose anti orbital hemisphere shows stronger water ice characteristics.[15]The reason for this asymmetry is not clear, but it may be related to the bombardment of charged particles in the magnetosphere from Uranus, which is stronger in the anti orbital hemisphere (due to the co rotation of the plasma).[15]High energy particles tend to sublimate water ice, and are trapped in the ice to formhydrateOfmethaneAnd darken other organic matters, leaving a dark carbon rich residue surface.[15]
Voyager 2 captured the highest resolution image of Triton in January 1986.
In addition to water, throughInfrared spectrometryThe other compounds identified on the surface of Triton are carbon dioxide, mainly concentrated in the anti orbital hemisphere.[21] The origin of carbon dioxide is not completely clear.It may be generated from local carbonates, or organic matter may be affected by solar ultraviolet radiation or high-energy charged particles from the Uranian magnetosphere.The latter process can explain its distributionAsymmetryBecause the reverse orbit hemisphere is more affected by the magnetosphere than the same orbit hemisphere.Another possible source is the release of trapped CO from water ice inside early Tritontwo, which may be related to the geological activities on this satellite in the past.[15]
The interior of Triton may be divided into rock cores wrapped by ice mantle.[20]If this is the case, the core radius is 520km (320 miles), accounting for 66% of the satellite radius, and its mass is about 58% of the satellite mass, which is determined by the composition of the satellite mass.The pressure of the Third Tianwei Center is about 0.58 GPa (5.8 kilobars),[20]The state of the ice mantle is unknown.If the ice contains enough ammonia or other antifreeze, Triton may have an underground ocean at the core mantle boundary, with a thickness of 50 kilometers (31 miles) and a temperature of about 190K.[20]The internal structure of Triton today depends largely on its thermodynamic history, which we know little about.
Surface characteristics
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Among Uranus's moons, Triton is between the brightness of dark Triton and Enceladus, and the brightness of bright Triton and Enceladus.[22]Its surface shows a steady reverse phase surge. At a phase angle of 0 °, the reflectivity decreases from 35% (geometric albedo) to 25% (about 1 ° angle).The content of Triton is relatively low, and the spectral albedo is about 17%.[22]Its surface is usually light red, but lighter than that of Triton.[23]However, the new impact sediment will turn blue, while the smooth plain and some grabens along the same track hemisphere near the Ursula impact crater are slightly red.[23-24]There may be asymmetry between the same orbit hemisphere and the reverse orbit hemisphere;[25]The former is 8% redder than the latter, but this difference is related to the smooth plain and may be accidental.[23]As the solar system ages, the reddening of the surface may be due to space weathering caused by charged particle bombardment and micro meteorite.[23]However, the color asymmetry of Triton is probably related to the increase of red matter.It comes from the outer layer of Uranus system, possibly from irregular satellites, which will be mainly deposited in the same orbital hemisphere.[25]
Scientists have discovered three types of geological features of Triton: impact crater, canyon and cliff.[26]The surface of Triton is not as many impact pits as that of Triton or Triton, so the surface is younger.[24]Largest known crater Gertrude[27](There may also be a degraded basin of roughly the same size) with a diameter of 326 km,[24]Some impact craters (e.g. Ursula and Jessica) are surrounded by bright impact jets (radiation lines) - relatively new water ice.All the large impact craters on Triton have flat plains and central peaks.The exception is the Ursula impact crater, which has a crater in its center.[24]In the west of Gertrude, there is an area with irregular terrain, namely the so-called "unnamed basin", which may be another impact basin with seriously reduced diameter.About 330 km (210 miles).[24]
The surface of Triton is pierced by huge faults and cliff systems.In some places, two parallel steep slopes mark the depression of the satellite crust,[21]The formation of graben is sometimes called canyon.[28]The most prominent canyon in Tricera is Messina Chasma, which stretches about 1500 kilometers (930 miles) from the equator to the South Pole.[26]The graben on Triton is 20-50 km (12-31 miles) wide and 2-5 km deep.[21]The cliffs unrelated to the canyon are called rupes, such as Rousillon Rupes near the Ursula impact crater.[26]At Voyager's image resolution, some steep areas near Ursula appear smooth.After the formation of most impact craters, these smooth plains may be resurfaced later in the geological history of Triton.The resurfacing may be endogenous, including fluid materials ejected from the interior (low temperature mania), or the nearby large impact crater may be covered by impact sputtering materials.[24]Graben is probably the youngest geological feature on Triton - they divide all impact craters, even smooth plains.[28]
The geology of Titania is affected by two competitive forces: impact crater[28]The former acts on the whole history of satellites and affects all surfaces.The latter process is also global in nature, but mainly in the formation of satellites[24]The original pitted terrain has been eliminated, which can explain that there are relatively few impact craters on the surface of satellites today.[21]Other resurfacing phenomena may occur later, resulting in a smooth plain.[21]In addition, the smoother plains may be covered by ejections from nearby impact pits.[28]Endogenous action is mainly manifested by geological tectonic activity, which eventually forms canyon terrain, that is, large cracks in the ice crust.[28]This crustal crack was formed during the expansion of the star of Triton, and the expansion rate of the star reached 0.7%.[28]
Surface features of the named Triton
Deep valley: the deep valley on Tianwei IIIShakespeareNames of place names in the works.
The presence of carbon dioxide on the surface indicates that Triton may have faint COtwoSeasonal atmosphere, much like Ganymede[29]Other gases, such as nitrogen or methane, are unlikely to occur because Titania's weak gravity cannot prevent them from escaping into space.The highest temperature (89 K) can be reached at the third summer solstice of Tianwei, and the vapor pressure content of carbon dioxide is about 300 μ Pa (3 nbar).[29]
On September 8, 2001, Triton eclipsed a bright star with an apparent magnitude of 7.2 (HD 106829), which is a good opportunity to accurately measure the diameter and ephemeris of Triton and detect any existing atmosphere.The data shows that there is no atmosphere with pressure up to 1 – 2 mPa (10 – 20 nbar).If it exists, it is thinner than Triton and Pluto[29]This upper limit is still several times higher than the maximum possible surface pressure of carbon dioxide, which means that there is essentially no limit on atmospheric parameters for measurement.[29]
The special geometry of the Uranus system causes the poles of the satellite to receive more solar energy[15]Due to COtwoThe vapor pressure of[29]It may lead to the condensation of Triton at low latitudes, where it can stably exist in shadow areas in the form of high albedo patches and ice.In summer, when the polar temperature reaches 85 – 90K,[26]Carbon dioxide sublimates and migrates to opposite poles and equatorial regions, causing acarbon cycle。The cold trap created by magnetospheric particles can remove the condensed carbon dioxide dry ice from it, thus splashing it from the surface.Since its formation 4.6 billion years ago, Triton is believed to have lost a lot of carbon dioxide.[15]
Origin and evolution
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Triton is believed to beAccretion diskOr secondary nebula, the gas orDust pan, or it may have been caused by a huge impact that tilted Uranus.[30]Astronomers do not know the exact composition of the sub nebula;However, compared with Saturn's satellite, the density of Triton and other Uranus satellites is higher, indicating that the nebula may contain less water ice.[14]In the secondary nebula forming satellites, nitrogen and carbon may be morecarbon monoxideandnitrogenInstead of ammonia and methane, it may contain less water ice (including CO and NtwoIs captured as inclusion compound) and more rocks, which indicates that their density is higher.[14]
The formation process of Triton may have lasted for thousands of years.[30]Accompanying the accumulation of influence, the satellite outer layer heats up.[31]The maximum temperature of about 250 K (− 23 ° C) was reached at a depth of about 60 km (37 miles).[31]After the formation of Triton, the underground rock stratum gradually cooled, and the temperature of the internal rock stratum increased due to the heat generated by the decay of radioactive elements contained in the rock.[14]The cooled outer rock stratum shrinks, while the inner rock stratum expands outward, which produces strong stress in the star crust, leading to the formation of cracks.This process lasted about 200 million years,[32]Formed the canyon seen today.This means that any endogenous tectonic activity stopped billions of years ago.[14]
Early accumulation of heat if someAntifreeze(e.g. ammonia), combined with the continuous decay of radioactive elements, may be strong enough to melt ice.Hydrated ammonia or salt[31]Further melting may lead to the separation of ice and rock, and the formation of core surrounded by ice mantle.A layer of liquid water ocean rich in dissolved ammonia may have formed at the core mantle boundary.[20]The eutectic point of this layer of ammonia water mixture is 176 K (- 97 ° C).[20]If the temperature is lower than this value, the ocean may freeze again now.The freezing of the ocean will lead to the expansion of the internal structure, which may be the reason for the formation of most canyon landforms.[33]However, the understanding of the geological evolution of Triton is still very limited.
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Only Voyager 2 took a close-up picture of the moon when it flew over Triton in January 1986.Since the shortest distance between Voyager 2 and Triton is only 365200 kilometers (226900 miles),[34]The optimal spatial resolution of the satellite image is about 3.4 km (only forTianwei FiveAnd Triton).[33]The images cover about 40% of the surface, but only 24% of the photos have the required accuracy of geological mapping.During the overflightsouthern hemispherePointing to the sun (like other satellites), it is impossible to study the northern (dark) hemisphere.[14]
Uranus system and Triton have not been visited by other spacecraft, and no exploration mission plan has been carried out in the future.One possibility that has been abandoned is pieCassiniGo from Saturn to Uranus for an expansion mission.Another proposed mission concept is the Uranus Orbiter and Probe Program, which was evaluated around 2010.Uranus has also been studied as part of the route of the pioneering interstellar probe concept "Innovative Interplanetary Explorer Program".Uranus orbiter[35]Listed as "NASAPlanetary scienceThe third priority flagship mission of the 10-year survey project is currently analyzing its conceptual design.[36]
