Pallene

Cassini image of Pallene transiting Saturn on October 16, 2010
Discovery
Discovered by	Voyager 2 (first discovery) Cassini Imaging Team[1]
Discovery date	June 1, 2004 (second discovery by Cassini-Huygens)
Designations
Designation	Saturn XXXIII
Pronunciation	/pəˈliːniː/[2]
Named after	Παλλήνη Pallēnē
Alternative names	S/1981 S 14 (first discovery) S/2004 S 2 (second discovery)
Adjectives	Pallenean /pælɪˈniːən/[3]
Orbital characteristics [4]
Epoch 20 June 2004 (JD 2453177.5)
Semi-major axis	212300 km[5]
Eccentricity	0.004[5]
Orbital period (sidereal)	1.009549 d[5]
Inclination	0.1810°±0.0014° (to Saturn's equator)
Satellite of	Saturn
Group	Alkyonides
Physical characteristics
Dimensions	5.76 × 4.16 × 3.68 km (± 0.14 × 0.14 × 0.14 km)[6]: 2
Mean diameter	4.46±0.14 km[6]: 2
Volume	46.5 km3[a]
Mass	(1.15±0.40)×1013 kg[6]: 3
Mean density	0.251±0.075 g/cm3[6]: 3
Surface gravity	0.011–0.016 mm/s2[6]: 3
Escape velocity	0.0007 km/s at longest axis to 0.0009 km/s at poles
Synodic rotation period	synchronous
Axial tilt	zero

Pallene /pəˈliːniː/ is a very small natural satellite of Saturn. It is one of three small moons known as the Alkyonides that lie between the orbits of the larger Mimas and Enceladus. It is also designated Saturn XXXIII.

Discovery

Pallene was discovered by the Cassini Imaging Team in 2004, during the Cassini–Huygens mission.^[7][8] It was given the temporary designation S/2004 S 2. In 2005, the name Pallene was provisionally approved by the IAU Division III Working Group for Planetary System Nomenclature,^[9] and was ratified at the IAU General Assembly in 2006. The name refers to Pallene, one of the Alkyonides, the seven beautiful daughters of the giant Alkyoneus.

After the discovery in 2004, it was realized that Pallene had been first photographed on August 23, 1981, by the space probe Voyager 2. It had appeared in a single photograph and had been provisionally named S/1981 S 14 and estimated to orbit 200,000 km from Saturn.^[10] Because it had not been visible in other images, it had not been possible to compute its orbit at the time, but recent comparisons have shown it to match Pallene's orbit.^[4]

Orbital characteristics

Pallene is visibly affected by a perturbing mean-longitude resonance with the much larger Enceladus, although this effect is not as large as Mimas's perturbations on Methone. The perturbations cause Pallene's osculating orbital elements to vary with an amplitude of about 4 km in semi-major axis, and 0.02° in longitude (corresponding to about 75 km). Eccentricity also changes on various timescales between 0.002 and 0.006, and inclination between about 0.178° and 0.184°.^[4]

Ring

In 2006, images taken in forward-scattered light by the Cassini spacecraft enabled the Cassini Imaging Team to discover a faint dust ring around Saturn that shares Pallene's orbit, now named the Pallene Ring.^[11][12] The ring has a radial extent of about 2,500 km. Its source is particles blasted off Pallene's surface by meteoroid impacts, which then form a diffuse ring around its orbital path.^[13][14]

Exploration

The Cassini spacecraft, which studied Saturn and its moons until September, 2017, performed a fly-by of Pallene on 16 October 2010, and 14 September 2011 at a distance of 36,000 kilometers (22,000 miles) and 44,000 kilometers respectively.^[15]