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Umbriel- the third largest satellite of Uranus: table of parameters, darkest surface, orbit, composition, name, Voyager-2 research, interesting facts.
The 19th century was a favorable time for scientists. We not only found the asteroid belt, but also found small planets and satellites. So one of interesting finds became the satellite of Uranus Umbriel. It is the third largest among the moons of Uranus and the darkest.
Discovery and name of Umbriel's satellite
In 1851, William Lassell found Umbriel and Ariel. True, William Herschel, 50 years earlier, claimed that he sees 4 satellites, but the observations were not confirmed.
Like the other 27 moons, Umbriel gets its name from a character in Shakespeare's creation. They were suggested by John Herschel.
This satellite is considered dark and the name itself with the prefix "umbra" (shadow) alludes to this.
Size, mass and orbit of Umbriel
It extends for 1170 km in diameter, but the spectrograph shows that most of represented by water ice, covering approximately 40% of the total mass. This may mean that the satellite consists of an outer ice crust centered around a rocky core. The darkness could have been created due to the contact of water ice with energy elements the planet's magnetosphere.
Thus, you found out which planet Umbriel is a satellite of.
The main parameters of the Umbriel satellite |
|||||
| Information about the opening | |||||
|---|---|---|---|---|---|
| opening date | October 24, 1851 | ||||
| pioneers | William Lassell | ||||
| Orbital characteristics | |||||
| Major axis | ? | ||||
| Eccentricity | 0,0039 | ||||
| Period of circulation | synchronized (turned to Uranus by one side) | ||||
| Mood | ~0° | ||||
| Satellite | uranium | ||||
| physical characteristics | |||||
| Diameter | 1169.4 ± 2.8 km | ||||
| Radius | 266,000 km | ||||
| Weight | 1.172 ± 0.35 10 21 kg | ||||
| Density | 1.39 ± 0.16 g/cm3 | ||||
| Albedo | 0,26 | ||||
Methane can decompose in ice elements, and other organic molecules become dark, leaving a carbon-enriched trail. Also dark color created by low albedo - the number of reflected EM rays.
The analysis showed the presence of water and carbon dioxide. So methane and organic substances still exist only in theory. But their presence can explain high level CO 2 in the posterior hemisphere.
The orbital period covers 4.1 days, which converges with the rotation period, which means the moon is in a gravitational block. Satellite Umbriel is distant from the planet Uranus at 266,000 km.
The only close photos of Umbriel came from Voyager 2, which flew past the satellite in 1986 at a distance of 325,000 km. The images reflected 40% of the surface, but only 20% were mined with the possibility of geological mapping. On that moment South side was turned to the Sun and the north remained in the shadow.
Interesting facts about Umbriel's moon
The surface of the satellite is littered with large crater scars, whose diameter can cover several hundred kilometers. The largest is Voloko, occupying 210 km. Wunda is most noticeable with a diameter of 131 km. Features a ring of bright material. There are also Fin, Peri and Zliden craters, whose names come from mythology.
Uranus' moon Umbriel is believed to have remained stable since the bombardment ceased. The only marks from the old days are canyons and dark polygons, complex shapes stretching for hundreds of kilometers. The polygons showed up in the images of Voyager 2. There are serious seasonal fluctuations.
Well this is interesting object. But for the time being, we cannot get to it again, since Mars and the nearest satellites are in priority. But scientists do not lose hope and believe that one day we will send a device there and collect more information. Below is a map of the Umbriel satellite.
Surface map of Umbriel
Umbriel, photographed by Voyager 2
Umbriel is a moon of Uranus discovered by William Lassell on October 24, 1851. Lassel also discovered Ariel at the same time. All 27 moons of Uranus are named after characters from plays by Alexander Pope and William Shakespeare. These names were suggested by John Herschel, son of William Herschel, the famous astronomer who discovered Titania and Oberon.
Umbriel
It is one of the five main satellites.
Both Umbriel are almost the same size, with a diameter of 1158 kilometers and 1170 kilometers respectively. The diameter is about one third of the diameter of the Earth.
It is the third largest moon, but only the fourth largest.
Scientists believe that most of it consists of water ice and about 40% is dense rocky material. 
Umbriel, photographed using light filters
It has the darkest surface of all moons. Albedo is the light that bounces off a surface and is very low, only 16%.
One revolution around Uranus takes approximately 4.1 days.
Since it is in synchronous orbit with the planet, it also takes 4.1 days to complete one revolution around the axis. The distance to the planet is on average 266 thousand kilometers. Uranus is the only planet in solar system, due to the large tilt of the axis (89 degrees) rotating lying on its side. Satellites rotate in the plane of the planet's equator. The north and south poles spend 42 years in the light and then 42 years in the dark. 
Discovered by William Lassell on October 24, 1851. Named after the gnome from the poem English poet Alexander Pope "The Abduction of the Lock".
Umbriel is mostly ice with a significant amount of rock. It may have a stone core covered by an icy mantle. Umbriel is the third largest moon of Uranus and has the darkest surface, reflecting only 16% of incident light.
Umbriel, covered with numerous impact craters reaching 210 kilometers in diameter, ranks second among the satellites of Uranus in terms of the number of craters (after Oberon).
Umbriel, like all the satellites of Uranus, was presumably formed in that surrounded the planet immediately after its formation.
studied the system of Uranus close range only one - . The flight took place in January 1986. Several images of Umbriel made it possible to study and map about 40% of its surface.
Opening and naming
Umbriel was discovered by William Lassell on October 24, 1851, along with another moon of Uranus, . Although William Herschel, the discoverer of Uranus, claimed at the end of the 18th century that he had observed four more moons of Uranus, his observations were not confirmed, and Herschel's right to be considered the discoverer of the remaining moons of Uranus is disputed.
All the moons of Uranus are named after characters in the works of William Shakespeare and Alexander Pope. The names of all four then-known moons of Uranus were proposed by William Herschel's son John in 1852 at the request of William Lassell. Umbriel is named after the melancholic dwarf from Alexander Pope's The Stolen Lock. The Latin word "umbra" means shadow. The moon is also designated as Uranus II.
Orbit
Uranus with satellites. Shot in the near infrared(Paranal observatory, 2002)
Umbriel's orbit is 266,000 kilometers from Uranus, the third-most distant of the five major moons of Uranus. The inclination of the orbit to the equator of the planet is very small. The orbital period of Umbriel is 4.1 earth days and coincides with the period of its rotation. In other words, Umbriel is a synchronous satellite of Uranus and always turns to it with the same side. The orbit of Umbriel passes entirely within the magnetosphere of Uranus, and this satellite has no atmosphere. Therefore, his back (along the way orbital movement) the hemisphere is constantly bombarded with particles of magnetospheric plasma, which orbit much faster than Umbriel (with a period equal to the period axial rotation Uranus). Perhaps this leads to the darkening of the rear hemisphere, which is observed on all satellites of Uranus, except for Oberon. The Voyager 2 flyby made it possible to detect a clear decrease in the concentration of ions in the magnetosphere of Uranus near Umbriel.
Since Uranus rotates around "on its side", and its equatorial plane roughly coincides with the plane of the equator (and orbit) of its large satellites, the change of seasons on them is very peculiar. Each pole of Umbriel is in complete darkness for 42 years and continuously illuminated for 42 years, and during the summer solstice the Sun at the pole almost reaches its zenith. The Voyager 2 flyby in January 1986 coincided with the summer solstice over south pole, while almost all North hemisphere was in complete darkness. Once every 42 years - during the equinox on Uranus - the Sun (and together with it) passes through its equatorial plane, and then mutual eclipses of its satellites can be observed. Several such events were observed in 2007-2008, including two Umbriel occultations of Titania on August 15 and December 8, 2007, and an Umbriel occultation of Ariel on August 19, 2007.
Umbriel does not currently have an orbital resonance with any of Uranus' moons. However, probably, at the beginning of its existence, it had a resonance of 1:3 with . This may have increased the eccentricity of Miranda's orbit, contributing to the internal heating and geological activity of that satellite, while Umbriel's orbit was largely unaffected. It is easier for the satellites of Uranus to get out of orbital resonance than for the satellites of or , since the oblateness and size of Uranus is less than that of more large giant planets. An example of this is Miranda, which went out of resonance (which is probably the reason for the anomalously large inclination of its orbit).
Composition and internal structure
Umbriel is the third largest and fourth largest moon of Uranus. Its density is 1.39 g/cm 3 . It follows from this that the satellite is largely composed of water ice, and denser components make up about 40% of its mass. These components can be stones, as well as macromolecular organic compounds known as tholins. Using infrared spectroscopy, water ice was found on the surface. Its absorption bands on the anterior hemisphere are more pronounced than on the posterior one. The reasons for this asymmetry are unknown, but it is assumed that this may be caused by the bombardment of the surface by charged particles from the magnetosphere of Uranus, which acts precisely on the trailing hemisphere (due to the joint rotation of the planet and plasma). These particles pulverize the ice, decomposing the (clathrate-forming) methane it contains and attacking other organic matter, leaving a dark, carbon-rich residue.
A shot of Umbriel using purple and light filters
Using infrared spectroscopy on the surface of Umbriel, in addition to water, carbon dioxide was detected, which is concentrated mainly in the rear hemisphere of the satellite. Origin carbon dioxide not quite clear. It could have formed on the surface from carbonates or organic matter under the influence of the sun ultraviolet radiation or charged particles coming from Uranus' magnetosphere. The latter can explain the asymmetry in the distribution of carbon dioxide over the surface of the satellite, because these particles bombard the trailing hemisphere. Another possible source of CO2 is the degassing of water ice in Umbriel's interior, which may be a consequence of the satellite's past geological activity.
Umbriel can be differentiated into a stone core and an icy mantle. If so, then the radius of the core (about 317 km) is approximately 54% of the radius of the satellite, and the mass of the core is about 40% of the mass of the satellite (the parameters are calculated based on the composition of Umbriel). In this model, the pressure at the center of Umbriel is about 0.24 GPa (2.4 kbar). Current state icy mantle is unclear, although the existence of a subsurface ocean is considered unlikely.
Surface
A snapshot of Umbriel, in which areas with different albedo are highlighted. Dark areas are highlighted in red, light areas in blue.
The surface of Umbriel is darker than the surfaces of all the other moons of Uranus and reflects less than half the light that Ariel reflects, although these moons are close in size. Umbriel has a very low Bond albedo - only about 10% (for comparison, Ariel has 23%). The surface of Umbriel exhibits an oppositional effect: as the phase angle increases from 0° to 1°, the reflectivity decreases from 26% to 19%. Unlike the other dark satellite Uranus - Oberon - the surface of Umbriel is slightly blue color. Young impact craters (such as Vanda crater) are even bluer. In addition, the anterior hemisphere is slightly redder than the posterior. This reddening is likely caused by cosmic weathering due to the bombardment of charged particles and micrometeorites since the formation of . However, Umbriel's color asymmetry could also be related to the accretion of reddish material coming from the outer part of the Uranian system (probably from irregular satellites). This substance should settle mainly on the anterior hemisphere. Other than this hemispheric difference, Umbriel's surface is relatively uniform in albedo and color.
The surface of the satellite is heavily cratered, but there are no craters with clearly visible light rays on it, unlike other satellites of Uranus. One of the proposed explanations for this is that the heat generated in the bowels of Umbriel during the era of its formation, for some reason, was not enough to melt the crust and gravitational differentiation. Therefore, the composition of Umbriel weakly depends on depth, and ejections of deep rocks around impact craters are indistinguishable from the main surface. However, the presence of canyons shows that endogenous processes once took place on the satellite; they probably led to a renewal of the surface and the destruction of old landforms.
| Crater | Origin of the name | Coordinates | Diameter (km) |
|---|---|---|---|
| Alberich | Alberich, the dwarf from the Nibelungenlied | 33.6°S sh. 42.2° E d.(G)(O) | 52 |
| Fin | Fin, a troll in Danish folklore | 37.4°S sh. 44.3° E d.(G)(O) | 43 |
| gob | Gob, King of the Dwarves | 12.7°S sh. 27.8° E d.(G)(O) | 88 |
| Canaloa | Kanaloa, Chief evil spirit in Polynesian mythology | 10.8°S sh. 345.7° E d.(G)(O) | 86 |
| Malingi | Malingee (Mutinga), the old witch in the mythology of the Australian aborigines |
22.9°S sh. 13.9° E d.(G)(O) | 164 |
| Minepa | Minepa, an evil spirit among the Makua people of Mozambique | 42.7°S sh. 8.2° E d.(G)(O) | 58 |
| Peri | Peri, evil spirits from Persian mythology | 9.2°S sh. 4.3° E d.(G)(O) | 61 |
| Setibos | Setibos, prince of darkness in Patagonia | 30.8°S sh. 346.3° E d.(G)(O) | 50 |
| Skind | Hurry, troll in Danish folklore | 1.8°S sh. 331.7° E d.(G)(O) | 72 |
| Woover | Woover from Finnish mythology | 4.7°S sh. 311.6° E d.(G)(O) | 98 |
| Vokolo | Wokolo, an evil spirit from the beliefs of the Bambara people living in West Africa | 30°S sh. 1.8° in. d.(G)(O) | 208 |
| Wanda | Wanda in Australian Aboriginal mythology | 7.9°S sh. 273.6° E d.(G)(O) | 131 |
| Sinister | Sinister, an evil spirit in Slavic mythology | 23.3°S sh. 326.2° E d.(G)(O) | 44 |
Now on Umbriel, the names have only one type of relief detail - craters. There are much more of them on this satellite than on Ariel and Titania, which indicates its lower endogenous activity. Of all the moons of Uranus, only Oberon surpasses Umbriel in the number of craters. Diameters known craters range from a few kilometers to 210 kilometers (for the Vokolo crater). All studied Umbriel craters have a central peak, but none have rays.
One of the main distinctive features Umbriel - Wanda crater with an unusual light circle at its bottom. This is the most prominent geological structure- the diameter is about 131 kilometers. A bright ring at the bottom of the crater may be made up of rock cut from Umbriel. impact. Neighboring craters such as Woover and Skind do not have such rings, but do have bright central peaks. Exploration of the limb of Umbriel has revealed a structure that may be a very large crater (about 400 kilometers in diameter and about 5 kilometers deep).
The surface of Umbriel, like other large satellites of Uranus, is dotted with a system of canyons directed from the northeast to the southwest. However, they have not been given names because the resolution of the images is insufficient for high-quality geological mapping.
The surface of Umbriel did not change after, so there are a lot of craters on it. The only signs of endogenous activity are canyons and dark polygons (areas complex shape tens to hundreds of kilometers in diameter). These polygons were discovered using precise photometry from Voyager 2 images. They are distributed more or less evenly over the entire surface of Umbriel with a predominant orientation from the northeast to the southwest. Some of these areas correspond to lowlands up to several kilometers deep and may be the result of early tectonic activity in Umbriel. At present, there is no explanation why the moon's surface is so dark and uniform. Perhaps it is covered with a thin layer of dark material brought to the surface by meteorite impacts or ejected by volcanoes. According to another version, the bark of Umbriel may consist entirely of dark matter, which makes it impossible for bright ejecta to appear around craters. However, this may be contradicted by the presence of a bright ring in the Vanda crater.
Origin and evolution
Like all large satellites Uranus, Umbriel probably formed from an accretion disk of gas and dust that either existed around Uranus for some time after the formation of the planet, or appeared in a powerful collision, which most likely gave Uranus a very large axial tilt. The exact composition of the nebula is unknown, but more high density satellites of Uranus compared to those of Saturn indicates that this nebula probably contained less water. Significant amounts of carbon and nitrogen may have been in the form of carbon monoxide (CO) and molecular nitrogen (N2) rather than ammonia and methane. A companion formed in such a nebula should contain less water ice (with CO and N2 clathrates) and large quantity stony rocks, and therefore have a higher density.
The formation of Umbriel by accretion probably continued for several thousand years. The collisions that accompanied the accretion caused heating of the satellite's outer layers. The maximum temperature (about 180 K) was reached at a depth of about 3 kilometers. After the completion of the formation, the outer layer cooled down, while the inner one began to heat up due to the decay radioactive elements enclosed in its rocks. The surface layer contracted due to cooling, while the heating inner layer expanded. This caused a strong mechanical stress in the crust of Umbriel, which could lead to the formation of faults. This process must have lasted about 200 million years. Thus endogenous activity on Umbriel must have ceased several billion years ago.
The heat from the initial accretion and subsequent decay of radioactive elements could be enough to melt the ice if it contains any antifreeze (for example, ammonia in the form of ammonium hydrate and salt). The melting could have led to the separation of ice from rock and the formation of a rocky core surrounded by an ice mantle. A layer could form at the boundary between the core and the mantle liquid water(ocean) saturated with dissolved ammonia. The eutectic temperature of this mixture is 176 K. If the ocean temperature was below this value, then it should have frozen long ago. Among all the satellites of Uranus, Umbriel was the least affected by endogenous surface transformation processes, although these processes may have affected Umbriel (as well as other satellites) in its early existence. Unfortunately, information about Umbriel is still very scarce and largely limited to research conducted by Voyager 2.
Research
Graphical reconstruction of a partial occultation of Uranus by Umbriel
The only images of Umbriel to date close-up were obtained by Voyager 2, which photographed the satellite during its exploration of Uranus in January 1986. smallest distance to the satellite was 325,000 kilometers (202,000 miles), and the most detailed images have a resolution of 5.2 kilometers. Images cover only 40% of the surface, and only 20% are captured with sufficient quality for geological mapping. During the flyby, the southern hemisphere of Umbriel (as well as other satellites) was facing the Sun, so the northern hemisphere was not illuminated and could not be studied. Neither Uranus nor Umbriel have been visited by other interplanetary probes, and there are no plans to visit in the foreseeable future.
The satellites of Uranus revolve in circular orbits located in the plane of the planet's equator, and in the same direction as the central body rotates. And since the rotation of Uranus is reversed, the movement of satellites is also reversed. Their orbits are steeply inclined to the plane of the ecliptic. Therefore, they move either "up" or "down". Observing such a strange movement of the satellites of Uranus, astronomers came to the conclusion that Uranus rotates lying on its side.
| Like Neptune and Saturn, Uranus has big number satellites (by 1997, 15 were discovered) and a system of rings. Largest dimensions(in kilometers) and mass (in fractions of the mass of Uranus) are typical for the first five (discovered from Earth) satellites. it Miranda(127 km, 10 -7), (565 km, 1.1 10 -5), (555 km, 1.1 10 -5), (800 km, 3.2 10 -5), (815 km, 3.4 10 -5). The last two satellites, according to theoretical estimates, experience differentiation, that is, redistribution various elements in depth, resulting in the formation of a silicate core, a mantle of ice (water and ammonia) and an ice crust. The heat released during differentiation leads to a noticeable heating of the interior, which can even cause their melting. The remaining 10 satellites of Uranus (Cordelia, Ophelia, Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind, Belinda, Pack) were discovered from the board spacecraft Voyager 2 in 1985-86. |
The explorers of the moons of Uranus have identified unusual fact: Ariel and Miranda have active volcanoes spewing... ice! On each of these satellites, several ice fields, similar to terrestrial lava fields, are clearly visible. It is quite possible that this ice consists of a mixture of ordinary frozen water with frozen methane and ammonia.
What is the cause of the eruptions themselves is not yet clear. However, it is known that water-methane-ammonia ice is more fluid than ordinary ice. At a temperature of -205°C, prevailing on the surface of Ariel and Miranda, such a mixture should be plastic enough to slowly flow down the slopes of the mountains.
