Pallene (moon)

Pallene

Cassini image of Pallene transiting Saturn on October 16, 2010
Discovery
Discovered by	Voyager 2 (first discovery) Cassini Imaging Team
Discovery date	June 1, 2004 (second discovery by Cassini-Huygens)
Designations
Designation	Saturn XXXIII
Pronunciation	/pəˈliːniː/
Named after	Παλλήνη Pallēnē
Alternative names	S/1981 S 14 (first discovery) S/2004 S 2 (second discovery)
Adjectives	Pallenean /pæləˈniːən/
Orbital characteristics
Epoch 20 June 2004 (JD 2453177.5)
Semi-major axis	212300 km
Eccentricity	0.004
Orbital period (sidereal)	1.009549 d
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)
Mean diameter	4.46±0.14 km
Volume	46.5 km3
Mass	(1.15±0.40)×1013 kg
Mean density	0.251±0.075 g/cm3
Surface gravity	0.011–0.016 mm/s2
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

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

Back-illuminated rings of Saturn as seen by Cassini on 15 September 2006. The faint Pallene ring is visible at the bottom left as indicated.

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

Pallene's crescent illuminated by Saturnshine, imaged by Cassini on 14 September 2011

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.

References

Sources

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• "Moonmade Rings". Cassini Imaging Central Laboratory for OPerationS. October 11, 2006. Archived from the original on 2012-02-05. Retrieved 2012-01-01.
• Green, Daniel W. E. (April 14, 1995). "Possible Satellites of Saturn". IAU Circular. 6162. Retrieved 2012-01-01.
• Green, Daniel W. E. (August 16, 2004). "S/2004 S 1 and S/2004 S 2" (discovery). IAU Circular. 8389: 1. Bibcode:2004IAUC.8389....1P. Retrieved 2012-01-01.
• Green, Daniel W. E. (January 21, 2005). "S/2004 S 1 and S/2004 S 2" (naming the moon). IAU Circular. 8471. Retrieved 2012-01-01.
• Green, Daniel W. E. (October 11, 2006). "Rings of Saturn (R/2006 S 1, R/2006 S 2, R/2006 S 3, R/2006 S 4)". IAU Circular. 8759: 1. Bibcode:2006IAUC.8759....1P. Retrieved 2012-01-01.
• Hedman, M. M.; Murray, C. D.; Cooper, N. J.; Tiscareno, M. S.; Beurle, K.; Evans, M. W.; Burns, J. A. (2008-11-25). "Three tenuous rings/arcs for three tiny moons". Icarus. 199 (2): 378–386. Bibcode:2009Icar..199..378H. doi:10.1016/j.icarus.2008.11.001. ISSN 0019-1035.
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• Spitale, J. N.; Jacobson, R. A.; Porco, C. C.; Owen, W. M. Jr. (2006). "The orbits of Saturn's small satellites derived from combined historic and Cassini imaging observations". The Astronomical Journal. 132 (2): 692–710. Bibcode:2006AJ....132..692S. doi:10.1086/505206.
• Thomas, P. C. (July 2010). "Sizes, shapes, and derived properties of the saturnian satellites after the Cassini nominal mission" (PDF). Icarus. 208 (1): 395–401. Bibcode:2010Icar..208..395T. doi:10.1016/j.icarus.2010.01.025. Archived from the original (PDF) on 2018-12-23. Retrieved 2015-09-04.
• Thomas, P. C.; Burns, J. A.; Tiscareno, M. S.; Hedman, M. M.; et al. (2013). "Saturn's Mysterious Arc-Embedded Moons: Recycled Fluff?" (PDF). 44th Lunar and Planetary Science Conference. p. 1598. Retrieved 2013-05-21.
• Thomas, P. C.; Helfenstein, P. (July 2020). "The small inner satellites of Saturn: Shapes, structures and some implications". Icarus. 344: 20. Bibcode:2020Icar..34413355T. doi:10.1016/j.icarus.2019.06.016. S2CID 197474587. 113355.

External links

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