Methone (moon)

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Methone
Methone PIA14633.jpg
Cassini image of Methone's leading side taken on 20 May 2012
Discovery
Discovered by Cassini Imaging Team [1]
Discovery date June 1, 2004
Designations
Pronunciation /mɨˈθn/ mi-THOH-nee
Adjectives Methonean
Orbital characteristics[3]
Epoch June 20, 2004 (JD 2453177.5)
194440±20 km
Eccentricity 0.0001
1.009573975 d[2]
Inclination 0.007°±0.003° (to Saturn's equator)
Satellite of Saturn
Physical characteristics
Mean radius
1.6±0.6 km [4]
Mean density
0.31+0.05
−0.03
 g/cm3
[5]
synchronous
zero

Methone is a very small natural satellite of Saturn lying between the orbits of Mimas and Enceladus.

Discovery and naming[edit]

Methone was first seen by the Cassini Imaging Team[1][6][7] and given the temporary designation S/2004 S 1. Methone is also named Saturn XXXII (32). The Cassini spacecraft has made two visits to Methone and its closest approach was made on May 20, 2012 with a minimum distance of 1,900 km (1,181 mi) from it.

The name Methone was approved by the IAU Working Group on Planetary System Nomenclature on January 21, 2005.[8] It was ratified at the IAU General Assembly in 2006. Methone (Greek Μεθώνη) was one of the Alkyonides, the seven beautiful daughters of the Giant Alkyoneus.

Characteristics[edit]

In May 2012, the Cassini spacecraft obtained its first close-up photographs of Methone, revealing an egg-shaped moonlet with a remarkably smooth surface, with no visible craters.[9] The moons Pallene and Aegaeon are thought to be similarly smooth.[10] There is a sharply defined distinctly (~13%) darker albedo region centered on Methone's leading point. UV and IR spectra gave no indication of a color difference between the two regions, suggesting that a physical rather than compositional difference may be responsible.[5] Increased exposure to electrons from Saturn's magnetosphere has been proposed to be responsible for thermal anomalies on the leading hemispheres of Mimas and Tethys,[11] and a similar irradiation anisotropy might be behind Methone's albedo pattern.[5]

Methone's mean radius is 1.6 km and its mass estimated to be 9×1012 kg.[12]

Assuming that Methone is in hydrostatic equilibrium, i.e. that its elongated shape simply reflects the balance between the tidal force exerted by Saturn and Methone's gravity, an estimate of its density can be calculated. The result is 0.31 g/cm3, among the lowest density values obtained or inferred for a Solar System body. This suggests Methone is composed of icy fluff, material that might be mobile enough to explain the lack of craters.[5][10]

Methone's orbit is visibly affected by a perturbing 14:15 mean longitude resonance with the much larger Mimas. This causes its osculating orbital elements to vary with an amplitude of about 20 km (12 mi) in semi-major axis, and 5° in longitude on a timescale of about 450 days. Eccentricity also varies on different timescales between 0.0011 and 0.0037, and inclination between about 0.003° and 0.020°.[3]

Material blasted off Methone by micrometeoroid impacts is believed to the source of the Methone Ring Arc, a faint partial ring about Saturn co-orbital with Methone discovered in September 2006.[13][14]

See also[edit]

References[edit]

Further reading[edit]

External links[edit]