Saturn’s F ring and its shepherd satellites, Prometheus and Pandora, are natural outcome of the final stage of formation of Saturn’s satellite system, according to a team of planetary scientists at Kobe University, Japan.
This composite image shows Saturn’s main rings, the F ring, and its shepherd satellites: the narrow F ring is located just outside of the outer edge of the main rings; slightly above and to the left of the center of the image are the shepherd satellites Prometheus (inner orbit) and Pandora (outer orbit). Image credit: NASA.
Discovered in 1979 by NASA’s Pioneer 11 spacecraft, Saturn’s F ring is a narrow ring of icy particles, located 3,400 km beyond the outer edge of the planet’s main ring system. It is between 30 and 500 km wide.
Enigmatically, the ring is accompanied on either side by two small satellites, Prometheus and Pandora, which are called shepherd satellites.
According to the latest satellite formation theory, Saturn used to have ancient rings containing many more particles than they do today, and satellites formed from spreading and accretion of these particles. During the final stage of satellite formation, multiple small satellites tend to form near the outer edge of the ring.
On the other hand, observations by NASA’s Cassini spacecraft indicate that the small satellites orbiting near the outer edge of the main ring system have a dense core.
In their simulations using computer systems at the National Astronomical Observatory of Japan, Kobe University researchers revealed that Saturn’s F ring and its shepherd satellites formed as these small satellites with a dense core collided and partially disintegrated.
In other words, the system of the F ring, Prometheus, and Pandora is a natural outcome of the formation process of Saturn’s ring-satellite system.
“Through this study, we were able to show that the current rings of Saturn reflect the formation and evolution processes of the planet’s satellite system,” said Dr Ryuki Hyodo of the Kobe University’s Department of Planetology, lead author on the study published in the journal Nature Geoscience.
“As plans are underway in and outside of Japan to explore the satellite system of Jupiter and the satellites of Mars, we will continue to unravel the origin of satellite systems, which is key to understanding the formation process of planetary systems,” added co-author Prof Keiji Ohtsuki, also of the Kobe University’s Department of Planetology.
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Ryuki Hyodo & Keiji Ohtsuki et al. Saturn’s F ring and shepherd satellites a natural outcome of satellite system formation. Nature Geoscience, published online August 17, 2015; doi: 10.1038/ngeo2508
