Polydeuces (moon)

Polydeuces (pronounced /ˌpɒlɨˈdjuːsiːz/ POL-i-DEW-seez, or as Greek Πολυδεύκης) is a very small natural satellite of Saturn that is co-orbital with Dione and librates around the trailing Lagrangian point (L₅). Its diameter is estimated to be about 3.5 km.^[3]

Polydeuces was discovered by the Cassini Imaging Team on October 24, 2004^[5] in images taken on October 21, 2004^,^[6]^,^[3] and given the temporary designation S/2004 S 5. Subsequent searches of earlier Cassini imaging showed it in images as far back as April 9, 2004^[5]. Polydeuces is also designated as Saturn XXXIV.

Of the known Lagrangian co-orbitals in the Saturn system, Polydeuces wanders the furtherest from its Lagrangian point. The libration takes it away from the L₅ by up to 31.4° in the direction away from Dione, and 26.1° towards it with a period of 790.931 days (for comparison L₅ trails Dione by 60°).^[2] Polydeuces' libration is large enough that it takes on some qualities of a tadpole orbit, as evidenced by the clear asymmetry between excursions towards and away from Dione. In the course of one such cycle, Polydeuces' orbital radius also varies by about ± 7660 km with respect to Dione's.^[5]

The name Polydeuces was approved by the IAU Working Group on Planetary System Nomenclature on January 21, 2005.^[7] In Greek mythology, Polydeuces is another name for Pollux, twin brother of Castor, son of Zeus and Leda.

[edit] References

^ ^a ^b The mean semi-major axis and period must be identical to Dione's.
^ ^a ^b ^c Spitale, J. N.; Jacobson, R. A.; Porco, C. C.; and Owen, W. M., Jr. (2006). "The orbits of Saturn's small satellites derived from combined historic and Cassini imaging observations" (^{[dead link]}). The Astronomical Journal 132: 692. doi:10.1086/505206.
^ ^a ^b ^c Porco, C. C.; et al.; Cassini Imaging Science: Initial Results on Saturn's Rings and Small Satellites, Science, Vol. 307, No. 5713 (February 25, 2005), pp. 1226-1236
^ based on density 0.5 − 2 g/cm³
^ ^a ^b ^c Murray, C. D.; et al. (2005). "S/2004 S 5: A new co-orbital companion for Dione". Icarus 179: 222. doi:10.1016/j.icarus.2005.06.009.
^ C.C. Porco, et al., IAUC 8432: Satellites and Rings of Saturn 2004 November 8 (discovery)
^ IAUC 8471: Satellites of Saturn 2005 January 21 (naming the moon)

[edit] External links

v • d • e Moons of Saturn

Generally listed in increasing distance from Saturn. Temporary names in italics.

Ring shepherds	moonlets · Pan · Daphnis · Atlas · Prometheus · ?S/2004 S 6 · ?S/2004 S 4 · ?S/2004 S 3 · Pandora

Co-orbitals	Epimetheus · Janus

Inner large (and Trojan)	Mimas · Methone · Anthe · Pallene · Enceladus · Tethys (Telesto • Calypso) · Dione (Helene • Polydeuces)

Outer large	Rhea (rings) · Titan · Hyperion · Iapetus

Inuit group	Kiviuq · Ijiraq · Paaliaq · Siarnaq · Tarqeq

Norse group	Phoebe · Skathi · S/2007 S 2 · Skoll · S/2004 S 13 · Greip · Hyrrokkin · Mundilfari · Jarnsaxa · S/2006 S 1 · S/2004 S 17 · Narvi · Bergelmir · Aegir · Suttungr · S/2004 S 12 · Bestla · Farbauti · Hati · S/2004 S 7 · Thrymr · S/2007 S 3 · S/2006 S 3 · Surtur · Kari · Fenrir · Ymir · Loge · Fornjot

Gallic group	Albiorix · Bebhionn · Erriapus · Tarvos

Rings of Saturn · Cassini-Huygens · Themis · Chiron