Research press release


Nature Geoscience

Origin of Saturn’s shepherd moons




関連するNews&Views記事でAurelien Cridaは、同様な過程が、「多数の細い環の少なくとも1つが羊飼い衛星をもつ天王星のシステムと、環の拡大による巨大惑星の衛星形成をより一般的に」説明できる可能性があると記している。

Saturn’s narrow F ring and its two tiny moons, Prometheus and Pandora, may be the product of a collision at the outer edge of the planet’s main ring system, according to a study published online in Nature Geoscience. The findings suggest that the seemingly unusual configuration of the F ring and its two faithful ‘shepherd moons’ may be a natural consequence of ring evolution around giant planets.

As Saturn’s main ring system evolved, ice particles clumped together to form moonlets, which eventually migrated outwards and merged with each other in collisions to form Saturn’s main moons. Saturn’s F ring, which lies beyond the main ring system, is thought to be the icy debris of a collision between two of these fragile moonlets. The ‘flock’ of icy F ring particles are confined to a well-defined, narrow band flanked on either side by Prometheus and Pandora, but how this shepherding arose remains unexplained.

Ryuki Hyodo and Keiji Ohtsuki simulated collisions between icy moonlets under conditions at the outer edge of Saturn’s main ring system. They find that if the moonlets are composed entirely of small icy particles, they completely disintegrate in the collision and only a ring remains. However, if the moonlets have denser cores, they may only partially disintegrate, forming a ring and leaving behind two remnant moons that match observations of the F ring system.

In an accompanying News & Views, Aurelien Crida writes that a similar process may also explain “features of the Uranian system, where at least one of a dozen narrow rings has shepherd moons…[and] the formation of giant planet satellites from the spreading of rings more generally.”

doi: 10.1038/ngeo2508


メールマガジンリストの「Nature 関連誌今週のハイライト」にチェックをいれていただきますと、毎週各ジャーナルからの最新の「注目のハイライト」をまとめて皆様にお届けいたします。