Lysithea (moon)

Lysithea /laɪˈsɪθiə/ is a prograde irregular satellite of Jupiter. It was discovered by Seth Barnes Nicholson in 1938 at Mount Wilson Observatory^[1] and is named after the mythological Lysithea, daughter of Oceanus and one of Zeus' lovers.^[10]

Lysithea

Near-infrared photograph of Lysithea (center) by the 2MASS survey
Discovery [1]
Discovered by	Seth B. Nicholson
Discovery site	Mt. Wilson Observatory
Discovery date	6 July 1938
Designations
Designation	Jupiter X
Pronunciation	/laɪˈsɪθiə/[2][3]
Named after	Λυσιθέα Lysithea
Adjectives	Lysithean /laɪˈsɪθiən/[4]
Orbital characteristics [5]
Epoch 27 April 2019 (JD 2458600.5)
Observation arc	79.87 yr (29,171 days)
Semi-major axis	0.0782144 AU (11,700,710 km)
Eccentricity	0.1478734
Orbital period (sidereal)	+258.57 d
Mean anomaly	27.18992°
Mean motion	1° 23m 32.227s / day
Inclination	26.29254° (to ecliptic)
Longitude of ascending node	343.46495°
Argument of perihelion	94.80010°
Satellite of	Jupiter
Group	Himalia group
Physical characteristics
Mean diameter	42.2±0.7 km (WISE)[6] 42.2±3 km (occultation)[7]: 6
Synodic rotation period	12.78±0.10 h[8]
Albedo	0.036±0.006[6]
Spectral type	C/P[6]
Apparent magnitude	18.2[9]
Absolute magnitude (H)	11.2[5]

Lysithea did not receive its present name until 1975; before then, it was simply known as Jupiter X. It was sometimes called "Demeter"^[11] from 1955 to 1975.

It belongs to the Himalia group, moons orbiting between 11 and 13 Gm from Jupiter at an inclination of about 28.3°.^[12] Its orbital elements are as of January 2000. They are continuously changing due to solar and planetary perturbations. It is gray^{[failed verification]} in color (B−V=0.72, V−R=0.36, V−I=0.74) and intermediate between C-type and P-type asteroids.^[13][6]

Lysithea observed by the Wide-field Infrared Survey Explorer (WISE) spacecraft in 2014

See also

• Irregular satellites
• Jupiter's moons in fiction