Perdita (moon)
| Perdita | |
|---|---|
 |
|
| Hubble picture from 2003 with Perdita, Cressida, Portia and Belinda | |
| Provisional or systematic name | S / 1986 U 10 |
| Central body | Uranus |
| Properties of the orbit | |
| Major semi-axis | 76,417 ± 1 km |
| Periapsis | 76,325 km |
| Apoapsis | 76,509 km |
| eccentricity | 0.0012 ± 0.0005 |
| Orbit inclination | 0.03 ± 0.3 (equatorial plane) ° |
| Orbital time | 0.638021 ± 0.000013 d |
| Mean orbital velocity | 8.7101 km / s |
| Physical Properties | |
| Albedo | 0.08 ± 0.01 |
| Apparent brightness | 24.0 likes |
| Medium diameter | 30.0 ± 6 km |
| Dimensions | ≈ 1.8 · 10 16 kg |
| surface | ≈ 2,800 km 2 |
| Medium density | ≈ 1.3 g / cm 3 |
| Acceleration of gravity on the surface | ≈ 0.0047 m / s 2 |
| Escape speed | ≈ 11.0 m / s |
| Surface temperature | ≈ −184 to −209 ° C / 64–89 K |
| discovery | |
| Explorer | |
| Date of discovery | May 18, 1999 |
| Remarks | Physical data relatively imprecise. |
Perdita (also Uranus XXV ) is the eleventh innermost and one of the smaller of the 27 known moons of the planet Uranus .
Discovery and naming
Perdita was discovered by Erich Karkoschka in 1999 on a photograph taken on January 18, 1986 by the Voyager 2 space probe when it passed Uranus. However, since no other recordings were available to confirm the existence of the moon, the discovery was not recognized. The discovery was announced on May 18, 1999 by the International Astronomical Union (IAU); the moon was initially given the provisional designation S / 1986 U 10 . However, it has not yet been confirmed, as it was assumed that it would be one of the already discovered inner moons of Uranus. In December 2001 the IAU decided to remove the entry from the list of known Uranus moons . On August 25, 2003, however, Mark R. Showalter and Jack Jonathan Lissauer found an object on recordings from the Hubble Space Telescope at the point where Perdita had to be according to the available calculations, and the IAU definitely confirmed its existence on September 3, 2003.
The moon was named after Perdita (Latin for "the lost"), the daughter of King Leontes of Sicily and Hermione in Shakespeare's romance Winter's Tale . Leontes has Hermione thrown into dungeon, believing that she was unfaithful to him with the Bohemian King Polixenes, and has the Oracle of Delphi questioned about it . Hermione gives birth to Perdita in the dungeon, whereupon Leontes, who is initially convinced of Hermione's guilt, instructs Lord Antigonus to abandon the child in the wilderness. After the oracle's exonerating answer for Hermione - which prophesied that Leontes would not have an heir until what was lost is found - Leontes receives news of the death of his son Mamilius, whereupon Hermione collapses supposedly dead. Antigonus abandons Perdita on the Bohemian coast , but is then killed by a bear. Perdita grew up for sixteen years with a Bohemian shepherd and his son Florizel, with whom she fell in love, but the couple kept their improper love a secret. However, when his father found out, the couple flees to Sicily. Leontes, who has since learned the truth, recognizes his missing daughter and is reconciled with Polixenes. This will bring Hermione back to life.
All the moons of Uranus are named after characters from Shakespeare or Alexander Pope . The first four Uranus moons discovered ( Oberon , Titania , Ariel , Umbriel ) were named after suggestions by John Herschel , the son of the Uranus discoverer Wilhelm Herschel . Later the tradition of naming was retained.
Track properties
Orbit
Perdita orbits Uranus in a prograde , almost perfectly circular orbit at an average distance of around 76,417 km (approx. 2,990 Uranus radii) from its center, i.e. 50,858 km above its cloud ceiling. The orbit eccentricity is 0.0012, the orbit is inclined 0.03 ° to the equator of Uranus .
Perdita is the outermost moon of the Portia group , which also includes Bianca , Cressida , Desdemona , Juliet , Portia , Rosalind , Cupid, and Belinda . These moons have similar orbits and similar spectral properties.
The orbit of the nearest inner moon Belinda is on average only 1,161 km away from Perdita's orbit, that of the next outer moon Puck 9,587 km. The Hubble measurements from 2003 show that Perdita does not follow an ideal Kepler orbit . It is in a 43:44 orbit resonance with the inner Belinda, 1,161 km away. In addition, it is close to a 7: 8 resonance with the Rosalind 6,490 km away .
Perdita is located in the middle of two Uranus rings, the inner ν (Ny) dust ring , the outer edge of which is on average around 6,500 km away from the Perdita orbit, and the inner edge of the outer μ (My) dust ring is just 9,600 km away, like Puck.
Perdita orbits Uranus in 15 hours, 18 minutes and 40.01 seconds. Since this is faster than the rotation of Uranus, Perdita rises in the west and sets in the east as seen from Uranus. Since Perdita moves close to the synchronous orbit, it turns out that Perdita only rises or sets once every 8 Uranus days on the horizon for a fictional observer, which means that she can be seen in the sky for almost 4 Uranus days.
rotation
It is believed that Perdita rotates synchronously and that its axis has an inclination of 0 °.
Physical Properties
Perdita has an estimated diameter of 30, according to other sources about 20 km. It can be assumed that Perdita does not have a spherical shape.
At 1.3 g / cm³, its mean density is significantly lower than the density of the earth and indicates that the moon is mainly composed of water ice .
Perdita has a very low albedo of 0.08, i.e. That is, 8% of the incident sunlight is reflected from the surface. It is therefore a very dark celestial body.
On its surface, the acceleration due to gravity is 0.0047 m / s², which is less than 1 ‰ of that on earth.
The mean surface temperature of Perdita is estimated to be between −184 ° C and −209 ° C (89–64 K ).
Otherwise, not much is known about this moon, as the probe images were taken at a great distance and therefore have a low resolution.
exploration
The Uranus system has been studied by earth-based observations since the Voyager 2 spacecraft passed, but Perdita was too small and faint to be located. It was only through observations with the Hubble space telescope that the orbit parameters of Perdita could be specified.
Web links
- IAUC 7171: S / 1986 U 10 May 18, 1999 (discovery)
- IAUC 8194: Satellites of Uranus September 3, 2003 (rediscovery)
- IAUC 8648: Satellites of Uranus December 29, 2005 (numbering and naming)
- Polish moon page: Perdita description and further links (English)
- Satellite Viewer Orbit simulation of the Uranus moons