Discovered by Cassini Imaging Science Team
Discovered on 24 October, 2004
Orbital characteristics
mean Semimajor axis 377,396 km[1]
Eccentricity 0.0192 [2]
Orbital period 2.736915 d [1]
Inclination 0.1774 ± 0.0015° [2]
Is a satellite of Saturn
Physical characteristics
Mean diameter 3.5 km[3]
Mass 1 − 5 ×1013 kg[4]
Mean density unknown
Surface gravity unknown
Rotation period assumed synchronous
Axial tilt unknown
Albedo unknown
Surface temperature
min mean max
Atmosphere none

Polydeuces (pol'-ee-dew'-seez, IPA /ˈpɑliˈdjuːsiz/, 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 on October 24, 2004 in images taken on October 21, 2004 by the Cassini imaging team 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 assymetry between excursions towards and away drom 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. In Greek mythology, Polydeuces is another name for Pollux, twin brother of Castor, son of Zeus and Leda.


  1. 1.0 1.1 The mean semi-major axis and period must be identical to Dione's.
  2. 2.0 2.1 2.2 J.N. Spitale et al (2006). "The orbits of Saturn's small satellites derived from combined historic and Cassini imaging observations". The Astronomical Journal 132: 692.
  3. 3.0 3.1 C. C. Porco et al. (2005), Cassini Imaging Science: Initial Results on Saturn's Rings and Small Satellites. Science 307 (5713): 1226-1236.
  4. Based on density 0.5 − 2 g/cm³
  5. 5.0 5.1 C.D. Murray et al (2005). "S/2004 S 5: A new co-orbital companion for Dione". Icarus 179: 222.

External links

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