Prometheus orbits Saturn in a near circular orbit with a radius of 139,380 km (87,000 miles), taking about 14 hours 43 minutes to complete one orbit. Its shape is highly irregular, with the three axis being about 119 x 87 x 61 km (74 x 54 x 38 miles). Prometheus is the shepherd moon for the inner edge of the F Ring.
Solar System - Saturn's Moons
Atlas orbits Saturn in a near circular orbit with a radius of 137,670 km (85,500 miles), taking about 14 hours 43 minutes to complete one orbit. It is quite small, and its shape is highly irregular, with the three axis being about 46 x 38 x 19 km (29 x 24 x 12 miles). Atlas, along with the moon Pan, has a distinctive "ridge" around its equator giving it the appearance of a flying saucer. The height of the ridge between about 3 km (2 miles) and 5 km (3 miles), and represents more than a quarter of Atlas' volume. From the time of its discovery in 1980, Atlas was believed to be the shepherd moon for the outer edge of the A Ring, but this is not the case, and the moons Janus and Epimetheus are now known t be responsible responsible. In 2004 a new, very faint ring was found in Atlas' orbit.
Pandora orbits Saturn in a near circular orbit with a radius of 141,720 km (88,060 miles), taking about 15 hours 5 minutes to complete one orbit. Its shape is highly irregular, with the three axis being about 103 x 80 x 64 km (64 x 50 x 40 miles). Pandora is the shepherd moon for the outer edge of the F Ring.
In the image to the right, the moons Pandora and Prometheus are shown "shepherding" the F Ring.
Janus orbits Saturn in a near circular orbit with a radius of about 151,460 km (94,175 miles), taking about 16 hours 40 minutes to complete one orbit, while Epimetheus' orbit is 50 km less taking about 30 seconds less to complete one orbit. There is a complex relationship between the two orbits that causes the two moons essentially to swap orbits about every four years. The process of orbit exchange is illustrated here.
Janus is of moderate size, but is highly irregular in shape, with the three axis being about 193×173×137 km (120×108×85 miles). It is heavily cratered with a number of large craters. Its very low density, less than 12% of the Earth's, and rather high reflectivity indicates it is probably icy and quite porous. Epimetheus is rather smaller at about 135×108×105 km (84×67×65 miles), similarly cratered and with similar density. There are suggestions that the two may have originated from a single parent body early in the life of the solar system.
There is a very faint dust ring around the orbits extending about 5,000 km. It is believed to originate with meteoroid collisions on the surface of the two moons raising dust particles that get distributed along their orbital path.
Janus & Epimetheus
Pan is the shepherd moon for the Encke Gap in Saturn's "A" ring, keeping the gap free of debris. It orbits very close to Saturn at a radius of only 133,584 km. It looks remarkably like a walnut, but is about 35 km wide by 23 km.
Daphnis orbits Saturn in the 42 km wide Keeler Gap within the "A" ring, every 14 hours and 15.5 minutes at a distance of 136,505 km. Its average diameter is about 7.8 km. Daphnis causes gravitational ripples on the inner edge of the gap, which precede it, and on the outer edge of the gap, that follow it. They are seen easily in the pictures to the left & right.
A 2005 Cassini image showing Daphnis' disc.
Saturn's moons are grouped as follows. Select to see details of the moon or the group of moons:
The image to the left is a new Cassini image of Prometheus.
Taken Sep 10th 2013.