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Prometheus

1. One of the small, inner moons of Saturn. It was discovered in 1980 from photos taken by Voyager 1 and is also known as Saturn XVI.
   
   

   Prometheus as imaged by Cassini on Jan. 27, 2010 from a distance of 36,000 km

   
   

   Prometheus as imaged by Voyager 2 on August 25, 1981

   A faint stream of material appears to connect the F ring to Prometheus, the white blob at the bottom, in this image taken by Cassini in July 2004

   
   Prometheus and Pandora act as shepherd moons for the inner edge of Saturn's F-ring. Prometheus is extremely elongated and has a number of ridges and valleys on its northern side. Although craters up to 20 km (12 miles) wide mark its icy surface, it appears to be less heavily cratered than its neighboring moons Pandora, Janus, and Epimetheus. Its low estimated density suggests that it may be a porous, icy body. See also Saturn, moons.
   
   
   

   discovery	1980, by S. Collins et al
   semimajor axis	139,353 km (85,590 miles)
   diameter	119 × 87 × 61 km (74 × 54 × 38 miles)
   mean density	0.5 g/cm3
   escape velocity	0.019 km/s (68 km/h, 43 mph)
   orbital period	0.613 days (14 hr 43 min.)
   orbital eccentricity	0.002
   orbital inclination	0.01°
   visual albedo	0.6

   
   
   

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2. A volcano on Io known as the Jovian moon's "Old Faithful." Prometheus has been active during every observation of it since it was first seen by Voyager 1, though its plume, which is 80 km tall, has migrated about 85 km to the west.



3. See also Project Prometheus.