Titania (moon)

William Herschel

Titania ( Uranus III) is the seventeenth of the 27 known moons of the planet Uranus. He is the viertinnerste the five major Uranian satellites and with a diameter of 1578 kilometers, the largest moon of Uranus and Neptune's largest moon Triton after the eighth largest moon in the solar system.

  • 3.1 size
  • 3.2 Internal structure
  • 3.3 Surface 3.3.1 Chasmata and Rupes
  • 3.3.2 crater terrain

Discovery and designation

Titania was discovered on January 11, 1787 along with Oberon as first and second moons of Uranus from Kurhannoverianischen astronomers William Herschel with his homemade telescope in Slough ( UK). Herschel had discovered Uranus around six years earlier. He announced the discovery of the two moons after ensuring the orbital parameters on February 9, 1787 known and observed the system from 1790 to 1796 on. Herschel gave later to the discovery of four more moons of Uranus, which later, however, proved to be non-existent. Almost 50 years after this discovery, Titania and Oberon were by no other than the telescope observed by Herschel more.

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

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

Originally Titania has been called " the first satellite of Uranus ", and 1848 was the moon of Uranus Lassell the name I though he sometimes numbering used Herschel's Uranus II. 1851 numbered Lassell, the previously known moons on the distances to the mother planet new, and has since been referred to as Titania Uranus III.

Web properties

Orbit

Titania Uranus orbits on a prograde, nearly perfectly circular orbit at an average distance of about 436,300 kilometers (about 17.070 Uranus radii ) from the center, or around 410,700 km on whose cloud tops. The orbital eccentricity is 0.0011, the orbit is inclined 0.079 degrees from the equator of Uranus.

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

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

Titania's orbit lies entirely in the magnetosphere of Uranus. The following hemispheres of ( almost) airless moons Titania as a result. Magnetosphärischem under constant attack from plasma which co-rotates with the planet This can lead to a darkening of the following hemisphere, which so far could be observed for all Uranian moons except Oberon. Titania also catches a magneto- spherical charged particles, which leads to an increased number of these particles in orbit and could be observed by the Voyager 2 spacecraft.

As Titania as Uranus orbits the sun practically relative to the rotation on the side, showing her the Northern or Southern hemisphere away at the time of the solstice, either directly to the sun or away from it, leading to extreme seasonal effects. This means that the poles of Titania are illuminated by the sun are in permanent darkness for half a Uranus year of 42 years or so. During the solstice, the sun is therefore close to the zenith over the poles. During the Voyager 2 flyby in 1986, which occurred almost at the solstice, which showed Südhemisphären of Uranus and its moons towards the sun, while the northern hemispheres were in complete darkness. During the equinox, in which the equatorial plane intersects with the direction to the earth and that also happens every 42 years mutual occultations and eclipses of the moons of Uranus Uranus are possible. A number of these rare events took place last from 2007 to 2008; Titania was covered by Umbriel on 15 August 2007, and on December 8, 2007.

Currently owns Titania no orbital resonance with other moons. 3.8 billion years ago estimated it was located but possibly in a 4:1 resonance with Ariel, which was possibly responsible for the internal heating of this moon.

Rotation

The rotation period is equal to the orbital period and Titania has with how the Earth's moon, a synchronous rotation, which therefore also takes place within 8 days, 16 hours, 56 minutes and 59 seconds. Your rotation axis is almost exactly perpendicular to its orbital plane.

Physical Properties

Size

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

From the size Titania is best compared with Oberon or Saturn 's moons Rhea and Iapetus. Of the entire moon has been able by Voyager 2 only about 40%, mainly the southern hemisphere - as with all Uranian moons - are explored in more detail.

The total area of ​​7.82 million km2 Titania is about, this is something more than the area of Australia.

Internal construction

Titania having an average density of 1.71 g/cm3, and its relatively high albedo is 0.27 i.e. 27% of the incident solar light is reflected from the surface. The low density and the high albedo suggest that about 50% Titania water ice, 30% silicate 20% rock and carbon compounds as well as other heavy organic compounds is composed of. The presence of water ice is supported by infrared spekroskopische studies from 2001 to 2005 that brought crystalline water ice on Titania's surface to light. This seems to be more present on Titania's leading hemisphere. The reason for this is unknown, but it seems from the bombardment of charged particles of Uranus ' magnetosphere to stem that has a stronger presence on the trailing hemisphere by the co- rotation of the plasma. These energetic particles tend to sputtering of water ice, the decomposition of methane trapped in ice as clathrate hydrate and the darkening of other organic material, resulting in carbon-rich deposits on the surface.

Apart from the water ice previously could only carbon dioxide ( CO2) can be spectroscopically proved beyond doubt and this compound is mainly focused on the following hemisphere. Its origin is not yet sufficiently clarified. It could be produced locally from carbonates or organic material through the influence of the charged particles of Uranus ' magnetosphere, or by solar ultraviolet radiation. The former hypothesis would explain the asymmetry in the distribution because the following hemisphere is under stronger influence of the magnetosphere. Another possible source is the outgassing of primordial CO2 that is trapped in water ice in Titania's heart. The release of CO2 from the inside is possibly connected with the past geological activity of the moon.

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

Surface

The surface of Titania has numerous craters, but far less than on the outer neighbors Oberon, and relatively newly formed ice fields and huge canyons and crustal fractures. This suggests a geological activity after the formation of the moon.

Of the major Uranian moons Titania lies in its brightness between the dark moons Umbriel and Oberon and the brighter moons Ariel and Miranda. The surface shows depending on the lighting angle high brightness effects; the reflectivity of 0.35 at a phase angle of 0 ° to 0.25 decreases rapidly from about 1 °. The Bond albedo is relatively low 0.17.

The surface shows a slightly reddish color, but less reddish than Oberon. The relatively fresh ice fields are bluish while the gentle plains appear slightly red on the leading hemisphere near the crater Ursula and along some ditches. There seems to exist a little dichotomy of the leading and the trailing hemisphere; the latter appears reddish to about 8%. This difference corresponds to the rolling plains and may be a coincidence. may be derived from the weathering by charged particles and impacts of micrometeorites since the formation of the solar system. The color asymmetry was probably built by the accretion of a reddish material from the outer Uranus system, possibly irregular moons that would be reflected mainly on the leading hemisphere.

The average surface temperature on Titania -203 ± 7 ° C (70 ± 7K). The temperature may rise to a maximum of -184 ° C and -213 ° C drop to.

On the surface, the acceleration due to gravity is 0.378 m/s2, corresponding to approximately 4% of the earthly.

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

Chasmata and Rupes

The canyons are called Chasma (plural Chasmata ), probably represent grave breaches caused by tectonic extension processes. They are the result of a global pressure, which was caused by the freezing of water or a water- ammonia solution in Titania's heart. The Chasmata on Titania are about 20 to 50 km wide and 2-5 km deep.

The most striking Canyon and the most striking feature of the surface at all is a huge fraction of about 1500 km in length called Messina Chasmata against which the Grand Canyon on Earth seems tiny. This structure consists of two faults that run from northwest to southeast and together form a more continuous trench. The canyon system cuts the most impact crater in its path and is cut by only a few craters, indicating a later development in the history of Titania, when the ice crust set off by an inner expansion.

From its expansion Chasmata ago Messina is with the Ithaca Chasma on Saturn's moon Tethys comparable; relative to the total size of the moon could be compared with the Valles Marineris on Mars or Kachina Chasma on Ariel him well.

The fractures that are not associated with the Chasmata be, (Latin for cliff) called Rupes. The largest and only notified of this kind is Rousillon Rupes, which is a level terrain. Since this structure is cut by only a very few craters, they must therefore also be relatively young.

The areas around some of these fractures appear in the resolution of the Voyager recordings as gentle levels that may have occurred later in the history of Titania's surface shaping, ie after most of the existing crater already existed. These transformations are perhaps endogenous nature, including the eruption of molten material from the interior ( Kryovulkanismus ), or they were leveled by Impaktmaterial nearby crater. The trenches are probably the youngest surface features of Titania; they cut all craters and even the levels.

Crater terrain

The surface of Titania is less heavily cratered than the surfaces of Oberon or Umbriel, which means that it is more recent. The diameter of the crater range from a few kilometers to 326 km for the largest known named Gertrude. Its crater rim rises about 2 km above the crater floor, and the central mountain has a diameter of about 150 km and is about 2 to 3 km high. That the crater rim and central peak are relatively flat compared to the overall size of the crater, points out that he has flattened after the passage of time by later processes.

To the west of the crater Gertrude is a terrain with irregular topography, the so-called Unnamed Basin (Unnamed Basin), which possibly represents another major highly weathered Impaktbecken with a diameter of 330 km.

Some craters, such as the above-mentioned Ursula or Jessica, are surrounded by bright deposits of Impaktmaterial and radiation systems that are composed of relatively fresh ice. Ursula is surrounded by rolling plains, which have the lowest crater densities of the whole Moon and thus must be relatively young. All the great crater on Titania have flat floors and central mountains, with the exception of Ursula, whose center is a depression. Ursula is cut by Belmont Chasma, which therefore still needs to be recent.

The geology of the surface was by two competing forces affect: Impacts and endogenous formation by surface renewal. The former took place over the whole period of the history of the moon, while the latter processes also had global influence, however, took place only at a certain time after the formation of Titania. They paved the heavily cratered terrain one, which explains the relative poverty craters visible on the surface today. For more episodes of the renewal were possibly an even later and led to the formation of layers. However, they might also have arisen due to the deposition of the nearby crater. The recent endogenous processes are mainly tectonic nature and caused the formation of the Chasmata, the huge cracks in the icy crust of the moon are caused by the global expansion of about 0.7%.

Atmosphere

The presence of carbon dioxide indicates a thin seasonal atmosphere, similar to that of Jupiter's moon Callisto. Other gases such as nitrogen or methane is likely not to exist, because they would escape into the space due to the low gravity of titania. If the maximum temperature of -184 ° C (89 K) during the summer solstice, the vapor pressure is about 3 nBar.

On September 8, 2001 covered the 7.2 Titania likes bright star HIP 106829, which was a rare opportunity to determine the diameter and ephemeris precisely and to discover a possible existing atmosphere. The data revealed no atmosphere at a pressure greater than 10-20 nBar. If it exists, it is thinner than that of Pluto or Neptune moon Triton by far. This upper limit is still several times greater than the maximum surface pressure of the carbon dioxide, which means that the measurements were not necessary for the parameter of the atmosphere.

The special geometry of the Uranus system leads the poles more solar energy than to the equatorial regions. Since the vapor pressure of CO2 is an increase factor for temperature, this may lead to an accumulation of carbon dioxide in the lower latitudes, where it can exist firmly on the regions of higher albedo and shaded areas in the form of dry ice. During the Titania - summer, when temperatures can reach 85 to 90 K, carbon dioxide sublimates and migrates to the equatorial regions and to the opposite pole, which is a type of CO2 cycle. The accumulated gas can be removed by the magnetic particles from the cold traps, the sputtering it away from the surface. It is believed that Titania has lost a significant portion of the existing carbon dioxide since its formation about 4.6 billion years ago.

Formation

Titania was probably formed by an accretion disk or by a sub- fog, which was possibly to Uranus during its time of origin or formed by the (still theoretical ) impact that could tip the planet on its side. The exact composition of this sub- nebula is not known, but, the higher densities of Uranus system compared to the lying closer to the Sun Saturn's moons to a relative lack of water out. Potentially significant amounts of nitrogen (N2 ) and carbon ( C ) in the form of carbon monoxide ( CO) and molecular nitrogen were present instead of ammonia (NH3 ) and methane ( CH4). Satellites that emerged from such a sub- fog would contain less water ice and CO and N2 as gas hydrate trapped in ice and more rock include, which would explain the higher densities.

The accretion process probably lasted several thousand years until the formation of Titania was completed. Models show that the accretion concomitant impacts would cause a heating of the outer shell of the moon at a temperature of about 250 K in a depth of up to 60 km. After the formation of this outer layer cooled, while Titania's affairs by the decomposition aufheizte radioactive elements in the rock. The cooling outer shell contracted, while the interior expanded. This caused great tension in the crust of the moon that led to breakthroughs in the crust and the formation of the canyon. This process, which lasted about 200 million years indicates that the endogenous formation of the surface was finished already billions of years ago.

Akkretionshitze the initial and subsequent decomposition radioactive elements may lead to a melting water ice when a freezing point -lowering substance, such as a salt of ammonia or in the form of ammonium hydroxide was present. This would lead to a separation of ice and rock (differentiation) of the core. In this case, a layer of liquid water would have led rich of dissolved ammonia, the boundary of mantle and core. The eutectic temperature of this mixture is 176 K. If the temperature falls below this value, the existing ocean today would probably already frozen over. This freezing presumably led to the extension of the interior, which was probably responsible for the formation of the bulk of Chasmata. Knowledge of the development of Titania is still very limited at present.

Research

Since the discovery in 1787 by William Herschel was 200 years except for the orbital parameters over Titania not much is known. The moon was too small and too far away to resolve it closer with ground-based telescopes.

On January 20, 1986 Titania was a relatively close distance of at least 365,200 kilometers passed by the Voyager 2 spacecraft and photographed and measured. The rotation axis of Uranus and Titania reported, due to the high axial inclination of the planetary system of 98 °, at which point toward Earth, so that the moons of Uranus could not be served individually as before at Jupiter and Saturn on the equatorial plane, but to their orbits like a target around the planet ruled and the planet had to be made virtually. This meant that all the moons of Uranus and only the southern hemisphere was photographed at intervals of about two days - the worst possible position for a flyby. In addition, you had to opt for a moon, as a close flyby at a necessarily large distances to all other conditional.

Since we wanted to draw on Voyager 2 to Neptune, the condition was a close Uranus flyby. This revealed that only the moon Miranda could be happening close. This was the best resolution of the photos is about 3.4 km; they show about 40 % of the surface, leaving only about 24 % were able to be used with the required quality for geological maps and crater count.

777026
de