Prometheus (moon)

Prometheus

Prometheus image from Cassini (December 26, 2009)
Discovery
Discovered by	Collins, Voyager 1
Discovery date	October, 1980
Orbital characteristics
Epoch 31 December 2003 (JD 2453005.5)
Semi-major axis	139380±10 km
Eccentricity	0.0022
Orbital period	0.612990038 d
Inclination	0.008°±0.004° to Saturn's equator
Satellite of	Saturn
Physical characteristics
Dimensions	135.6 × 79.4 × 59.4 km
Mean radius	43.1±2.7 km
Volume	≈ 340000 km3
Mass	(1.595±0.015)×1017 kg
Mean density	0.48±0.09 g/cm³
Surface gravity	0.0013–0.0058 m/s²
Escape velocity	≈ 0.019 km/s
Rotation period	synchronous
Axial tilt	zero
Albedo	0.6
Temperature	≈ 74 K

Not to be confused with the asteroid 1809 Prometheus.

Prometheus is an inner satellite of Saturn. It was discovered in 1980 (some time before October 25) from photos taken by the Voyager 1 probe, and was provisionally designated S/1980 S 27.

In late 1985 it was officially named after Prometheus, a Titan in Greek mythology. It is also designated Saturn XVI (16). Pronunciation for Prometheus is /proʊˈmiːθiəs/, US dict: prō·mē′·thē·əs; Greek: Προμηθεύς.

Prometheus is extremely elongated, measuring approximately 136 km × 79 km × 59 km (85 mi × 49 mi × 37 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 a lot of uncertainty in these values, however, and so this remains to be confirmed.

Interactions with F Ring and other moons

Prometheus acts as 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.

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. The most appreciable changes in their orbits occur approximately every 6.2 years, when the periapsis of Pandora lines up with the apoapsis of Prometheus, when 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.

Selected images

Prometheus pulling material from the F Ring  Prometheus tugging kinks into the F Ring  Voyager 2 (August 25, 1981) image  Cassini image (with moon's Saturn-facing end at lower right) reveals a surface covered with a blanket of fine material.  Image from Jan. 27, 2010. Saturnshine illuminates the moon's night side.  Brightened version of same image  Prometheus flyby (December 6, 2015)

Animations

Play media Prometheus collides with the F ring, pulls a streamer, and leaves behind a dark channel. 12 seconds 107 kbit/s  Play media Movie of Prometheus and the F Ring looped once. 5 seconds 48 kbit/s

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Media related to at Wikimedia Commons

• Prometheus Profile at NASA's Solar System Exploration site
• The Planetary Society: Prometheus
• 3-D anaglyph view of Prometheus