Prometheus (moon)

Prometheus

Prometheus image from Cassini (December 26, 2009)
Discovery
Discovered by	Collins, Voyager 1
Discovery date	October, 1980
Orbital characteristics [1]
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 [2]
Mean radius	43.1±2.7 km [2]
Volume	≈ 340000 km^3 [2]
Mass	(1.595±0.015)×10^17 kg [2]
Mean density	0.48±0.09 g/cm³ [2]
Surface gravity	0.0013–0.0058 m/s² [2]
Escape velocity	≈ 0.019 km/s
Rotation period	synchronous
Axial tilt	zero
Albedo	0.6
Temperature	≈ 74 K

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.^[3]

In late 1985 it was officially named after Prometheus, a Titan in Greek mythology.^[4] It is also designated Saturn XVI (16).^[5] Pronunciation for Prometheus is /prəˈmiːθiəs/,^[6] US dict: prə·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.^[7][8]

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.^[9] The most appreciable changes in their orbits occur approximately every 6.2 years,^[1] 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.^[1]

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

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

References

Citations

1. Spitale Jacobson et al. 2006.
2. Thomas 2010.
3. IAUC 3532.
4. IAUC 4157.
5. USGS: Planet and Satellite Names and Discoverers.
6. "Prometheus". Oxford Dictionaries. Oxford University Press. Retrieved 2016-01-21.
7. Lakdawalla, E. (2014-07-05). "On the masses and motions of mini-moons: Pandora's not a "shepherd," but Prometheus still is". Planetary Society. Retrieved 2015-04-17.
8. Cuzzi, J. N.; Whizin, A. D.; Hogan, R. C.; Dobrovolskis, A. R.; Dones, L.; Showalter, M. R.; Colwell, J. E.; Scargle, J. D. (April 2014). "Saturn’s F Ring core: Calm in the midst of chaos". Icarus 232: 157–175. doi:10.1016/j.icarus.2013.12.027. ISSN 0019-1035.
9. Renner et al. 2005.

Sources

• Marsden, Brian G. (October 31, 1980). "Satellites of Saturn" (discovery). IAU Circular 3532. Retrieved 2011-12-29.
• Marsden, Brian G. (January 3, 1986). "Satellites of Saturn and Pluto" (naming the moon). IAU Circular 4157. Retrieved 2011-12-29.
• Renner, Stéfan F.; Sicardy, Bruno; French, Richard G. (March 2005). "Prometheus and Pandora: Masses and orbital positions during the Cassini tour". Icarus 174 (1): 230–240. Bibcode:2005Icar..174..230R. doi:10.1016/j.icarus.2004.09.005.
• Spitale, J. N.; Jacobson, R. A.; Porco, C. C.; Owen, W. M., Jr. (2006). "The orbits of Saturn's small satellites derived from combined historic and Cassini imaging observations" (PDF). The Astronomical Journal 132 (2): 692–710. Bibcode:2006AJ....132..692S. doi:10.1086/505206.
• Thomas, P. C. (July 2010). "Sizes, shapes, and derived properties of the saturnian satellites after the Cassini nominal mission" (PDF). Icarus 208 (1): 395–401. Bibcode:2010Icar..208..395T. doi:10.1016/j.icarus.2010.01.025.
• USGS/IAU (July 21, 2006). "Planet and Satellite Names and Discoverers". Gazetteer of Planetary Nomenclature. USGS Astrogeology. Retrieved 2011-12-29.

External links

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Media related to Prometheus (moon) at Wikimedia Commons

• "Cassini–Huygens: Multimedia-Videos / Soft Collision". NASA. Archived from the original on 29 October 2007. Prometheus slowly collides with the diffuse inner edge of Saturn's F ring ... pulls a streamer of material from the ring and leaves behind a dark channel.
• Prometheus Profile at NASA's Solar System Exploration site
• The Planetary Society: Prometheus
• 3-D anaglyph view of Prometheus