Hyodo Ryuki, a second-year student in the Doctoral Program, and Professor Ohtsuki Keiji of the Graduate School of Science at Kobe University have revealed that Saturn's F ring and its shepherd satellites are natural by-products of the final stage of formation of Saturn's satellites. Their research results will be published in Nature Geoscience on August __.

Saturn, which is the second largest planet in our solar system after Jupiter, is known to possess multiple rings and satellites. In 1979, Pioneer 11 discovered the F ring located outside the main ring system that extends tens of thousands of kilometers.

The F ring is very thin with a width of only a few hundred kilometers and possesses two shepherd satellites called Prometheus and Pandora, which orbit inside and outside the ring, respectively. Although the Voyager and Cassini spacecrafts have made detailed observations of the F ring and its shepherd satellites since their discovery, their origin was unclear.

According to the latest satellite formation theory, which includes contributions by Hyodo and Ohtsuki, Saturn used to possess rings containing many more particles than they do today, and satellites formed from aggregates of these particles. During the final stage of satellite formation, multiple small satellites formed in close orbit.

The data obtained by Cassini indicated that the small satellites orbiting near the outer edge of the main ring system have a dense core. In their simulations using the computing facilities at the National Astronomical Observatory of Japan, Hyodo and Ohtsuki revealed that the F ring and its shepherd satellites formed as these small satellites collided and partially disintegrated. In other words, the F ring and its shepherd satellites are natural by-products of the formation process of Saturn's satellite system.

This new revelation should help elucidate the formation of satellite systems both within and outside our solar system. For example, the above formation mechanism can also be applied to the rings and shepherd satellites of Uranus, which are similar to those of Saturn.

Hyodo remarked, "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."

"As plans are underway in and outside of Japan to explore the satellite system of Jupiter and the satellites of Mars," said Ohtsuki, "we will continue to unravel the origin of satellite systems, which is key to understanding the formation process of planetary systems."