Moon Perdita

Perdita's discovery was very complicated, as the first photographs of Perdita were taken by the Voyager 2 spacecraft in 1986, but it was not recognized from the photographs for more than a decade. In 1999, the moon was noticed by Erich Karkoschka and reported. But because no further pictures could be taken to confirm its existence, it was officially demoted in 2001. However, in 2003, pictures taken by the Hubble Space Telescope managed to pick up an object where Perdita was supposed to be, finally confirming its existence.

Perdita

Discovery
Discovered by	Erich Karkoschka / Voyager 2
Discovery date	May 18, 1999 (in images dating back to January 18, 1986)
Designations
Designation	Uranus XXV
Pronunciation	/ˈpɜːrdətə/
Adjectives	Perditean /pɜːrdəˈtiːən/
Orbital characteristics
Mean orbit radius	76,417 ± 1 km
Eccentricity	0.0012 ± 0.0005
Orbital period (sidereal)	0.638021 ± 0.000013 d
Inclination	0.0 ± 0.3° (to Uranus' equator)
Satellite of	Uranus
Physical characteristics
Mean radius	13.3±0.7 km
Surface area	~2220 km2
Volume	~9850 km3
Mass	~(4.93–8.87)×1015 kg
Mean density	0.5–0.9 g/cm3
Surface gravity	~0.002–0.003 m/s2
Escape velocity	~0.007–0.009 km/s
Synodic rotation period	synchronous
Axial tilt	zero
Albedo	0.08 ± 0.01 (assumed)
Temperature	~64 K

Following its discovery in 1999, it was given the temporary designation of S/1986 U 10. It was named Perdita (Latin for 'lost') after the daughter of Leontes and Hermione in William Shakespeare's play The Winter's Tale. The moon is also designated Uranus XXV.

The moon orbits between Belinda and Puck. The above-mentioned Hubble measurements prove that Perdita does not follow a direct Keplerian motion around Uranus. Instead, it is clearly caught in a 43:44 orbital resonance with the nearby moon Belinda, and from this resonance it has been determined that Belinda's mass is 26 times that of Perdita. It is also close to an 8:7 resonance with Rosalind.

Perdita belongs to the Portia group of satellites, which also includes Bianca, Cressida, Desdemona, Portia, Juliet, Cupid, Rosalind and Belinda. These satellites have similar orbits and photometric properties. Little is known about Perdita apart from its orbit, radius of 13.3 km and geometric albedo of 0.08.

• Moons of Uranus