Pallene (moon)

Pallene

Pallene in September 2010
Discovery
Discovered by	Voyager 2 (first discovery) Cassini Imaging Team
Discovery date	June 1, 2004 (second discovery by Cassini-Huygens)
Designations
Alternative names	Saturn XXXIII S/1981 S 14 (first discovery) S/2004 S 2 (second discovery)
Orbital characteristics
Epoch June 20, 2004 (JD 2453177.5)
Semi-major axis	212,280 ± 5 km
Eccentricity	0.0040
Orbital period	1.153745829 d
Inclination	0.1810 ± 0.0014° (to Saturn's equator)
Satellite of	Saturn
Physical characteristics
Dimensions	2.9×2.8×2.0 km
Mean radius	2.5 ± 0.6 km
Rotation period	synchronous
Axial tilt	zero

Pallene (/pəˈliːniː/ pə-LEE-nee; Greek: Παλλήνη) 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 as Saturn XXXIII (33).

Discovery

Discovery image of Pallene in 2004 from the Cassini probe

Pallene was discovered by the Cassini Imaging Team in 2004, during the Cassini–Huygens mission. 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, 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. 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.

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°.

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. 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.

Exploration

The Cassini–Huygens spacecraft, which is currently studying Saturn and its moons, performed a fly-by of Pallene on 16 October 2010, at a distance of 36,000 kilometeres (22,000 miles).

External links

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• Media related to at Wikimedia Commons
• Pallene Profile by NASA's Solar System Exploration