Polydeuces.space

Trojan moon of Saturn · Dione’s trailing L5 Lagrange point

Polydeuces

Saturn XXXIV · S/2004 S 5

A three-kilometre moon that trails Dione around Saturn — and wanders farther from its Lagrange point than any other trojan moon.

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Polydeuces at a glance
Object typeTrojan (co-orbital) moon of Saturn[1]
LocationTrailing L5 Lagrange point of Dione[1]
DiscoveredImages of 21 Oct. 2004, Cassini Imaging Science Team[1]
Named21 January 2005, after Polydeuces (Pollux)[1]
Diameter≈ 3 km[1]
SurfaceProbably smooth, coated with icy particles from Enceladus[1]
Mean distance≈ 377,600 km from Saturn[3]
Orbital period≈ 2.74 days[3]
Eccentricity≈ 0.019[3]

A trojan moon

Polydeuces shares Dione’s orbit, sitting around Dione’s trailing L5 Lagrange point. Helene occupies the leading point.[1][2]

The biggest wanderer

Perturbations from nearby moons make Polydeuces drift away from its Lagrange point periodically. Of Saturn’s four known trojan moons, it shows the largest displacement.[1]

Dusted with Enceladus ice

About 3 km across, Polydeuces is thought to have a smooth surface coated with fine icy particles from the cryovolcanic plumes of Enceladus.[1]

Spotted by blinking

The Cassini Imaging Science Team found it on 24 October 2004 in images taken on 21 October, using the blink comparison technique. Pre-discovery images went back to April 2004.[1]

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Orbit

With Dione and Helene, Polydeuces orbits Saturn every 2.74 days at about 377,600 km, between Tethys and Rhea.[1][3]

Saturn Tethys (295 thousand km)Dione (377.7 thousand km) farthest ≈ 384.8 thousand km closest ≈ 370.4 thousand km
Top-down orbit of Polydeuces to scale, computed from JPL orbital elements (a ≈ 377.6 thousand km, e ≈ 0.019).[3] Tethys and Dione orbits shown for comparison.[3] Mean orbital elements; this moon’s orbit is almost perfectly circular and lies close to Saturn’s ring plane.

The name

Polydeuces is another name for Pollux, twin brother of Castor and son of Zeus and Leda.[1]

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Lagrange points and trojan moons

How a tiny moon can share an orbit with a big one.

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How Cassini found Polydeuces

Blink comparison, pre-discovery images and a quick confirmation.

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Castor and Pollux in the sky

From Saturn’s moon to the Gemini twins.

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Sources

  1. Polydeuces (moon) — Wikipedia
  2. Polydeuces — NASA Science
  3. Planetary Satellite Mean Elements — NASA JPL Solar System Dynamics
  4. Lagrange point — Wikipedia
  5. Dione (moon) — Wikipedia

Figures are rounded; where sources differ we note it. Spotted an error? Tell us.