Polydeuces (moon)

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Saturn's moon Polydeuces
Saturn's moon Polydeuces
Discovered by Cassini Imaging Science Team
Discovery date October 24, 2004
Pronunciation /ˌpɒlɨˈdjsz/ POL-i-DEW-seez
Saturn XXXIV (34)
S/2004 S5
Orbital characteristics[1]
377,396 km [a]
Eccentricity 0.0192 [1]
2.736915 d [a]
Inclination 0.1774 ± 0.0015° [1]
Satellite of Saturn
Physical characteristics
Dimensions 3 × 2.5 × 2 km[2]
Mean radius
1.3 ± 0.4 km[2]
Mass 1–5 ×1013 kg[b]
assumed synchronous

Polydeuces, or Saturn XXXIV (34), is a small natural satellite of Saturn that is co-orbital with the moon Dione and librates around its trailing Lagrangian point (L5). Its diameter is estimated to be 2–3 km.[2] It is pronounced /ˌpɒlɨˈdjsz/ POL-i-DEW-seez; Greek: Πολυδεύκης. Dione's other co-orbital moon is Helene, which is bigger and located at the leading L4 point.[3]

Polydeuces was discovered by the Cassini Imaging Team on October 24, 2004,[4] in images taken on October 21, 2004,[5][6] 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.[4] Of the four known Lagrangian co-orbitals in the Saturn system ('trojan moon'), Polydeuces wanders the farthest from its Lagrangian point: its distance behind Dione varies from 33.9° to 91.4° with a period of 790.931 days (for comparison, L5 trails Dione by 60°).[1] Polydeuces's 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's orbital radius also varies by about ± 7660 km with respect to Dione's.[4]

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.


  1. ^ a b The mean semi-major axis and period must be identical to Dione's.
  2. ^ based on density 0.5–2 g/cm³

See also[edit]


Further reading[edit]

  • Green, Daniel W. E. (November 8, 2004). "Satellites and Rings of Saturn" (discovery). IAU Circular 8432. Retrieved 2011-12-31. 
  • Green, Daniel W. E. (January 21, 2005). "Satellites of Saturn" (naming the moon). IAU Circular 8471. Retrieved 2011-12-31. 
  • Murray, C. D.; Cooper, N. J.; Evans, M. W.; Beurle, K. (December 1, 2005). "S/2004 S 5: A new co-orbital companion for Dione". Icarus 179 (1): 222–234. Bibcode:2005Icar..179..222M. doi:10.1016/j.icarus.2005.06.009.  edit
  • Porco, C. C.; Baker, E.; Barbara, J.; Beurle, K.; Brahic, A.; Burns, J. A.; Charnoz, S.; Cooper, N.; Dawson, D. D.; Del Genio, A. D.; Denk, T.; Dones, L.; Dyudina, U.; Evans, M. W.; Giese, B.; Grazier, K.; Helfenstein, P.; Ingersoll, A. P.; Jacobson, R. A.; Johnson, T. V.; McEwen, A.; Murray, C. D.; Neukum, G.; Owen, W. M.; Perry, J.; Roatsch, T.; Spitale, J.; Squyres, S.; Thomas, P.; Tiscareno, M. (February 25, 2005). "Cassini Imaging Science: Initial Results on Saturn's Rings and Small Satellites". Science 307 (5713): 1226–1236. doi:10.1126/science.1108056. PMID 15731439.  edit
  • 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.  edit

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