Miranda ( Uranus V) is the fourteenth of the known 27 as well as the smallest and innermost of the five large moons of the planet Uranus. It is characterized by a very complex surface.
- 3.1 size
- 3.2 Internal structure
- 3.3 Surface 3.3.1 Coronae
- 3.3.2 Regiones
- 3.3.3 Rupes
- 3.3.4 crater
- 4.1 The collision theory
- 4.2 The orbital resonance theory
Discovery and designation
Miranda was discovered on 16 February 1948 as the fifth moon of Uranus the Dutch- American astronomer Gerard Kuiper Peter at McDonald Observatory in Texas, 161 years after the discovery of Titania and Oberon.
Miranda is the daughter of the magician Prospero, the rightful Duke of Milan, in Shakespeare's The Tempest. Miranda was the first of a total of 10 moons, named after a character in this play.
All the moons of Uranus are named after characters from Shakespeare or Alexander Pope, which on a proposal of the astronomer John Herschel, the son of Uranus discoverer William Herschel back.
Miranda Uranus orbits on a prograde, nearly perfectly circular orbit at an average distance of about 129,872 kilometers (about 5,081 Uranus radii ) from the center, or around 104,300 km on whose cloud tops. The orbital eccentricity is 0.0013, the orbit is inclined 4.338 degrees from the equator of Uranus.
The orbit of the next inner moon Mab is on average 31,650 kilometers away from Miranda's orbit, that of the next outer moon Ariel about 61,000 km.
Miranda is the first moon of Uranus system, which is located entirely outside of the rings. The outer edge of the outermost μ ( My) dust ring is removed about 27,000 km from the Miranda orbit.
Miranda orbits Uranus in 1 day, 9 hours, 55 minutes and 25 seconds.
Since Miranda 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 Miranda 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 which also happens every 42 years, mutual occultations and eclipses of the moons of Uranus Uranus are possible. A number of these events took place recently in 2007 and 2008.
Miranda currently owns no orbital resonance with other moons. In his history he was but possibly in a 5:3 resonance with Ariel and a 3:1 resonance with Umbriel, who may have been responsible for the internal heating of Miranda.
The rotation period is equal to the orbital period and Miranda has with how the Earth's moon, a synchronous rotation, which therefore also takes place within one day 9 hours, 55 minutes and 25 seconds. Its rotation axis is exactly perpendicular to its orbital plane.
Miranda is slightly irregular in shape with dimensions of 481 × 468.4 × 465.8 km. It is noteworthy that the equatorial diameter in the case of Miranda is greater than the polar diameter, which is extremely rare in the solar system at large to medium-sized moons. The surface has a high albedo of 0.32, i.e., 32 percent of the incident light from the sun being reflected. This corresponds approximately to the reflectivity of deserts to the earth. From the size Miranda is best compared with Saturn's moon Enceladus and Neptune moon Proteus. Of the entire moon has been able by Voyager 2 only 45 to 50%, mainly the southern hemisphere - as with all Uranian moons - are explored in more detail.
Miranda is predominantly ( about 80 %) of water ice, with proportions of silicate rock, and carbon compounds such as methane assembled. Due to the composition, it has a low density of 1.214 g/cm3. The acceleration of gravity at its surface is 0.079 m/s2, which is less than 1 % of the earth.
Miranda was photographed and measured in January 1986 flyby of the Voyager 2 spacecraft. Its surface has extreme distortions, fragmentary pattern and a network of canyons that are up to 20 km deep with Verona Rupes. No other known celestial bodies has such structures, which is why Miranda is the most geologically interesting of the moons of Uranus.
The maximum surface temperature of Miranda is -189 ° C ( 84 K); on average there are only about an estimated -213 ° C (60 K).
The total area of Miranda is about 700,000 km2, which corresponds approximately to the size of France, Austria, Switzerland and Slovenia put together.
The most conspicuous structures on Miranda's surface are the so-called coronae (Latin for wreaths ), which differ greatly from the cratered area. On them only few craters are present, indicating a younger age. General coronae are slightly darker than the surroundings, the albedo is in brighter regions 0.32 to 0.33, in darker from 0.25 to 0.26. The surrounding coronae brighter highlands have an albedo of 0.29 on average.
This structure, which is known for its angled arrangement and Inverness (Scotland ), a town in Shakespeare's Macbeth is named, is a valley in the surrounding highlands and measures in its maximum extension 234 km. The brightness variations in this formation are exceptionally large, the albedo varies from 0.20 to at least 0.40. In the formation of this complex area, one starts from a cryovolcanic origin.
Inverness Corona is located near the geographic south pole of Miranda, who immediately connects itself to the highlands at the end of the longer length of the light angle and the border. To the north it is bounded by the Argier Rupes, a deep grave system with cliffs, extending from the Elsinore Corona to the Verona Rupes.
This is reminiscent of a racetrack structure that is similar to structures on Jupiter's moon Ganymede, named after Elsinore (English name for Helsingor, Denmark) to Shakespeare's Hamlet. The parallel furrows south of the equator from west extend about 30 ° to the east, and are called Naples sulcus, perform at the east end a change of direction of more than 90 ° and consist to the north under the name Syracuse sulcus continued. To the north and to the east the Elsinore Corona is limited by the stark, Ephesus regions and the mountainous regions Sicilia. The largest crater of Elsinore Corona, which intersects the border of the highlands to the south is called Stephano. The Elsinore corona extends over 323 km, ie nearly 70 % of the total diameter of the moon.
Arden Corona, after the Ardennes forest ( Ardennes ) in Shakespeare's As you like it is named, extends over 318 km and is similar in length however, so the Elsinore Corona is much wider. This structure appears to be caused by large-scale upwelling. The only previously named craters of Arden Corona stands out because of its high brightness and Gonzalo is called.
The highlands surrounding the coronae is divided into four regions previously named, the Mantua Regio Regio Dunsinane, Sicilia Region and Ephesus regions are called. The first two are reminiscent of the highlands on the Earth's Moon or Saturn's moon Mimas. The Mantua Regio is the most extensive structure on Miranda and has an extension of 399 km, while Dunsinane Regio has a diameter of 244 km.
The Sicilia Region (extension 170 km) is characterized by very high mountains and has grooves similar to those on Mars moon Phobos. The Ephesus regions (extension 225 km), which was only in 1997 so named and to the north adjoins the Elsinore Corona, provides its own, particularly irregularly furrowed and scarred region dar. on the previous recordings is only a small part of this region visible.
The regions were named as all surface structures on Miranda after Shakespeare plays, including Mantua (Italy ) from Romeo and Juliet and Two Gentlemen of Verona, the Dunsinane Hill from Macbeth, Sicilia from The Winter's Tale and Ephesus ( Turkey), from The Comedy of Errors.
Miranda has two broad grave systems, noticeable by their steep cliffs high sided (Latin Rupes ) and in the solar system are unique. In particular, Verona Rupes, which is named after the location of the action in Shakespeare's Romeo and Juliet, is particularly known as the height of this cliff is an estimated 20 miles and, by their proximity to day - night boundary at the time of the Voyager 2 flyby in the surface structures of the body through the shadows are especially visible, could be photographed the media. Verona Rupes separates the Sicilia Region of the Dunsinane Regio and extends in a north-south direction.
This grave system, named after Algiers in Shakespeare's The Tempest, runs from the Elsinore Corona starting in west-east direction and separates the Inverness Corona in the south of the Sicilia Region in the north. The slopes on the north side of Argier Rupes are significantly higher and flatter toward the east; at its foothills, near which is the largest named crater Alonso, the Verona Rupes connects. For Inverness Corona out are the relationships are not as high, but much steeper.
Only seven of the International Astronomical Union ( IAU) of the countless impact craters on Miranda have yet been officially named, according to the USGS nomenclature all after characters from Shakespeare's The Tempest. The named craters are all on the cratered highlands, with the exception of the crater Stephano, which is located on the edge of Elsinore Corona. The largest named crater is 25 km Alonso. Five of the seven crater names were also used for the discovered from 1997 to 2003 nine outer irregular moons of Uranus, especially for Francisco, Ferdinand, Prospero, Stephano and Trinculo.
The collision theory
Due to the ubiquity of impact craters and the mosaic-like structure of the surface, this theory was created soon after the Voyager 2 flyby. Thus, the moon in its history became apparent once or several times torn apart and continued as a result of its own gravity back together. The cause was believed to be either strong tidal forces of Uranus have ripped the moon, or he was shattered by a collision with another celestial body, the latter theory seemed to be more likely. This theory is now considered obsolete, as could find no evidence of such events more.
The orbital resonance theory
Theoretical models of the orbital evolution of the Uranus system provide evidence that Miranda had been in their early days in a 5:3 orbital resonance with the moon Ariel and a 3:1 resonance with Umbriel. This theory, which is now generally considered to be valid is supported by the fact that today's observed orbital inclination is about ten times higher than in the other regular Uranian moons. Then Miranda became more and after three rounds in the gravitational sphere of influence of Umbriel and after five rounds in those of Ariel. In both cases, Miranda was thus provided additional orbital energy. This meant that Miranda's orbit became increasingly eccentric and in its periapsis in stronger influence of Uranus ' fell tidal forces. The result was that parts of Miranda's heart heated the, diapirs of warmer water ice rose up and tectonic processes put in motion that formed the structures visible today as the coronae and the fold mountains. After a certain time, however, Miranda escaped the resonance with Umbriel, as evidenced by the lower oblateness of Uranus and the - was favored larger moons compared to Jupiter and Saturn - relatively speaking. As a result, the moon cooled off again.
After the discovery in 1949 by Gerard Kuiper several decades was out of the orbital parameters over Miranda is not much known. The moon was too small and too far away to resolve it closer with ground-based telescopes. The big breakthrough came in January 1986 flyby of the Voyager 2 space probe to Uranus. The axis of rotation of the planet had, as a result of the high axial inclination 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 ruled around the planet and the planet had to be taken virtually. This meant that at intervals of about two days of all moons of Uranus only the southern hemisphere could be photographed - 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 Miranda was close to happening that. For the participating scientists because of their size and the supposed assumption of a geologically dead world like Saturn 's moon Mimas, initially was not the preferred destination So it was pure luck that the most interesting surface of the Uranus system could be taken up close. Voyager 2 passed Miranda on 24 January 1986 at a distance of 29,000 miles and sent a series of high-resolution images back to Earth.