Daphnis.space

Shepherd moon of Saturn · Keeler Gap, Saturn’s A ring

Daphnis

Saturn XXXV · S/2005 S 1

The wavemaker: an eight-kilometre moon that carves ripples into the edges of Saturn’s rings.

Key factsTelescope picker
Daphnis at a glance
Object typeInner shepherd moon of Saturn[1]
LocationKeeler Gap in the A ring (≈ 42 km wide)[1]
DiscoveredImages of 1 May 2005; announced 10 May 2005[1]
Diameter≈ 7.8 km[1]
PorosityOver 60% (expected, from low density)[1]
Mean distance≈ 136,500 km from Saturn[3]
Orbital period≈ 14 hours[2]
Named2006, after a shepherd-poet of Greek myth[1]

A moon inside the rings

Daphnis orbits in the Keeler Gap, about 42 km wide, within Saturn’s A ring.[1] It is one of only two known shepherd moons orbiting inside the main rings, with Pan.[1]

Making waves

Daphnis raises gravitational ripples on the gap’s edges. Waves on the inner edge lead the moon and those on the outer edge lag, because ring material at different distances moves at different speeds.[1][2]

Predicted before it was seen

A moon in Daphnis’s position was inferred from ripples at the Keeler Gap edges before it was photographed.[1] Cassini discovery images were taken on 1 May 2005.[1]

A ridged, porous body

Close-up images from January 2017 show an irregular moon with a mostly smooth surface, a few craters and an equatorial ridge. Its low density suggests a porosity above 60%.[1]

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Orbit

Daphnis orbits about 136,500 km from Saturn in about 14 hours.[3][2] Its slight eccentricity changes its distance by about 9 km, and its tilt moves it up and down by about 17 km.[1]

Saturn Mimas (186 thousand km) farthest ≈ 136.5 thousand km closest ≈ 136.5 thousand km
Top-down orbit of Daphnis to scale, computed from JPL orbital elements (a ≈ 136.5 thousand km, e ≈ 0).[3] Mimas's orbit shown for comparison.[3] Mean orbital elements; this moon’s orbit is almost perfectly circular and lies close to Saturn’s ring plane.

See the rings yourself

Saturn’s rings are not visible to the naked eye, but a small telescope shows them.[4] Try our telescope picker.

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Daphnis, the wavemaker

How a small moon sculpts the edges of the Keeler Gap.

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Saturn’s two moons inside the main rings

Daphnis and Pan compared.

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Daphnis’s ridge and porous body

What Cassini’s closest images revealed in 2017.

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Sources

  1. Daphnis (moon) — Wikipedia
  2. Daphnis — NASA Science
  3. Planetary Satellite Mean Elements — NASA JPL Solar System Dynamics
  4. Rings of Saturn — Wikipedia
  5. Pan (moon) — Wikipedia

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