Methone.space

Small inner moon of Saturn · Between Mimas and Enceladus

Methone

Saturn XXXII · S/2004 S 1

Saturn’s egg-shaped moon: smooth, craterless, and one of the least dense bodies known.

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Methone at a glance
Object typeSmall inner moon of Saturn[1]
DiscoveredJune 1, 2004, Cassini Imaging Team[2]
ShapeEgg-shaped triaxial ellipsoid[1]
SizeMean radius ≈ 1.6 km[2]
Density≈ 0.31 g/cm³ — among the lowest known[1]
Resonance14:15 with Mimas[1]
Closest Cassini flybyMay 20, 2012, ≈ 1,900 km[1]
Mean distance≈ 194,700 km from Saturn[3]
Orbital period≈ 24 hours[2]

An egg in orbit

Cassini’s close-up images in May 2012 revealed a remarkably smooth, non-spherical moonlet.[1] NASA says it’s hard not to think of an egg.[2]

Icy fluff

Methone’s smoothness suggests an equipotential surface of mobile icy fluff, which might explain its lack of craters.[1]

Lighter than water

Assuming its shape balances Saturn’s tides and its own gravity, Methone’s density is about 0.31 g/cm³ — among the lowest values for any Solar System body.[1]

Rocked by Mimas

A 14:15 resonance with Mimas makes Methone’s semi-major axis vary by about 20 km over about 450 days.[1]

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Orbit

Methone orbits about 194,700 km from Saturn in about 24 hours.[3][2]

Saturn Mimas (186 thousand km)Enceladus (238.4 thousand km) farthest ≈ 195.1 thousand km closest ≈ 194.3 thousand km
Top-down orbit of Methone to scale, computed from JPL orbital elements (a ≈ 194.7 thousand km, e ≈ 0.002).[3] Mimas and Enceladus orbits shown for comparison.[3] Mean orbital elements; this moon’s orbit is almost perfectly circular and lies close to Saturn’s ring plane.

Methone ring arc

Material blasted off Methone is believed to feed a faint partial ring discovered in September 2006.[1]

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Why Methone is shaped like an egg

Tides, spin and gravity in balance.

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One of the least dense bodies known

What 0.31 g/cm³ means.

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Methone’s two-tone surface

Bright and less bright regions.

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Sources

  1. Methone (moon) — Wikipedia
  2. Methone — NASA Science
  3. Planetary Satellite Mean Elements — NASA JPL Solar System Dynamics
  4. Alcyonides — Wikipedia
  5. Hydrostatic equilibrium — Wikipedia

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