Pasiphae (moon)

Not to be confused with Pasithee (moon).

Pasiphae /pəˈsɪfeɪ.iː/, formerly spelled Pasiphaë,^[10] also known as Jupiter VIII is one of the outermost and the biggest of retrograde irregular satellite of Jupiter. As an irregular moon with an eccentric orbit, it gets as far as 35.9 million km from Jupiter.

Pasiphae

Pasiphae photographed by the Haute-Provence Observatory in August 1998
Discovery[1]
Discovered by	Philibert J. Melotte
Discovery site	Royal Observatory, Greenwich
Discovery date	27 January 1908
Designations
Designation	Jupiter VIII
Pronunciation	/pəˈsɪfeɪ.iː/[2][3]
Named after	Πασιφάη Pāsiphaē
Alternative names	1908 CJ
Adjectives	Pasiphaëan /ˌpæsɪfeɪˈiːən/[4]
Orbital characteristics[5]
Epoch 2026-01-01
Observation arc	110.34 yr (40,303 days)
Periapsis	12.3 million km
Apoapsis	35.9 million km
Semi-major axis	24.1 million km
Eccentricity	0.490
Orbital period (sidereal)	–763.7 d
Mean anomaly	227.2°
Mean motion	0° 29m 54.168s / day
Inclination	155.6° (to ecliptic)
Longitude of ascending node	73°
Argument of perihelion	268°
Satellite of	Jupiter
Group	Pasiphae group
Physical characteristics
Mean diameter	57.8±0.8 km[6]
Mass	1.72×1017 kg (calculated)
Mean density	1.70 g/cm3 (assumed)[7]
Albedo	0.044±0.006[6]
Spectral type	C[6]
Apparent magnitude	16.9[8]
Absolute magnitude (H)	10.1[9]

Discovery and Naming

It was discovered in 1908 by Philibert Jacques Melotte.^[1][11] The moon was first spotted on a plate taken at the Royal Greenwich Observatory on the night of 28 February 1908. Inspection of previous plates found it as far back as January 27. It received the provisional designation 1908 CJ, as it was not clear whether it was an asteroid or a moon of Jupiter. The recognition of the latter case came by April 10.^[12]

Later named after the mythological Pasiphaë, wife of Minos and mother of the Minotaur from Greek legend. Pasiphae did not receive its present name until 1975;^[13] before then, it was simply known as Jupiter VIII. It was sometimes called "Poseidon"^[14] between 1955 and 1975.

Orbit

The diagram illustrates its orbit in relation to other retrograde irregular satellites of Jupiter. The eccentricity of selected orbits is represented by the yellow segments (extending from the pericentre to the apocentre). The outermost regular satellite Callisto is located for reference..

Pasiphae orbits Jupiter on a high eccentricity (0.490) and high inclination (about 157°) on a retrograde orbit with an average distance of 24.1 million km, but it gets as far as 35.9 million km from Jupiter.^[5] The orbital elements are continuously changing due to solar and planetary perturbations.

It gives its name to the Pasiphae group, a group of retrograde moons jupiters with semi-major axes spread over 22–25 million km, inclinations between 141° and 158°, and higher eccentricities between 0.22 and 0.44.

Pasiphae is also known to be in a secular resonance with Jupiter (tying the longitude of its perijove with the longitude of perihelion of Jupiter).^[15]

Physical characteristics

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

With a diameter estimated at 58 km (Albedo 4.4%),^[6] Pasiphae is the largest retrograde and third largest irregular satellite after Himalia and Elara.

Spectroscopical measurements in infrared indicate that Pasiphae is a spectrally featureless object, consistent with the suspected asteroidal origin of the object. The satellite appears pale red (colour indices V=17.22 B-V=0.74, R-V=0.38) though it falls into the grey color-class of C-type asteroids.^[16]

Origin

Pasiphae probably did not form near Jupiter but was captured by Jupiter later. Pasiphae is believed to be a fragment from a captured asteroid along with other Pasiphae group satellites.^[17][18]

See also

• Irregular satellite