Astronomy:Prometheus (moon)

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Short description: Moon of Saturn
Prometheus
Prometheus 12-26-09b.jpg
Prometheus image from Cassini (December 26, 2009)
Discovery
Discovered byStewart A. Collins
D. Carlson
Voyager 1
Discovery dateOctober, 1980
Designations
Designation
Saturn XVI
Pronunciation/prəˈmθəs/[1]
Named afterΠρομηθεύς Promētheys
AdjectivesPromethean, -ian /prəˈmθən/[2]
Orbital characteristics[3]
Epoch 31 December 2003 (JD 2453005.5)
139380±10 km
Eccentricity0.0022
Orbital period0.612990038 d
Inclination0.008°±0.004° to Saturn's equator
Satellite ofSaturn
GroupInner shepherd moon of the F Ring
Physical characteristics
Dimensions137.0 × 81.0 × 56.2 km
(± 1.0 × 2.8 × 0.8 km)[4](p2)
Mean diameter85.6±1.4 km[4](p2)
Volume327740±1710 km3[5](p4)
Mass(1.59720±0.00072)×1017 kg[lower-alpha 1]
Mean density0.4873±0.0026 g/cm3[5](p4)
0.0007–0.0056 m/s2[4](p3)
0.018 km/s at longest axis
to 0.028 km/s at poles
Rotation periodsynchronous
Axial tiltzero
Albedo0.6
Physics≈ 74 K


Prometheus /prəˈmθəs/ is an inner satellite of Saturn. It was discovered in 1980 (on October 24) from photos taken by the Voyager 1 probe, and was provisionally designated S/1980 S 27.[6]

In late 1985 it was officially named after Prometheus, a Titan in Greek mythology.[7] It is also designated Saturn XVI.[8]

Prometheus is extremely elongated, measuring approximately 137 km × 81 km × 56 km (85 mi × 50 mi × 35 mi). It has several ridges and valleys and a number of impact craters of about 20 km (12 mi) diameter are visible, but it is less cratered than nearby Pandora, Epimetheus, and Janus. From its very low density and relatively high albedo, it is likely that Prometheus is a very porous icy body. There is much uncertainty in these values, however, and so this remains to be confirmed.

Interactions with F Ring and other moons

Prometheus is a shepherd satellite for the inner edge of Saturn's narrow F Ring. Pandora orbits just outside the F Ring, and has traditionally been viewed as an outer shepherd of the ring; however, recent studies indicate that only Prometheus contributes to the confinement of the ring.[9][10]

Images from the Cassini probe show that the Promethean gravitational field creates kinks and knots in the F Ring as it 'steals' material from it. The orbit of Prometheus appears to be chaotic, due to a series of four 121:118 mean-motion resonances with Pandora.[11] The most appreciable changes in their orbits occur approximately every 6.2 years,[3] when the periapsis of Pandora lines up with the apoapsis of Prometheus, as they approach to within approximately 1400 km. Prometheus is itself a significant perturber of Atlas, with which it is in a 53:54 mean-longitude resonance.[3]

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Animations

Notes

  1. Calculated from the standard gravitational parameter GM = (1.06602±0.00048)×10−2 km3·s–2 given by Lainey et al. (2023), divided by the gravitational constant G = 6.6743×10−2 km3·kg–1·s–2.[5]

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