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Discovery of 12 satellites of Saturn exhibiting orbital clustering

Abstract

The giant planets in the Solar System each have two groups of satellites. The regular satellites move along nearly circular orbits in the planet's orbital plane, revolving about it in the same sense as the planet spins. In contrast, the so-called irregular satellites are generally smaller in size and are characterized by large orbits with significant eccentricity, inclination or both. The differences in their characteristics suggest that the regular and irregular satellites formed by different mechanisms: the regular satellites are believed to have formed in an accretion disk around the planet, like a miniature Solar System, whereas the irregulars are generally thought to be captured planetesimals1. Here we report the discovery of 12 irregular satellites of Saturn, along with the determinations of their orbits. These orbits, along with the orbits of irregular satellites of Jupiter and Uranus, fall into groups on the basis of their orbital inclinations. We interpret this result as indicating that most of the irregular moons are collisional remnants of larger satellites that were fragmented after capture, rather than being captured independently.

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Figure 1: This sketch compares the orbital properties of the irregular satellites of the giant planets.

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Acknowledgements

The Canada–France–Hawaii telescope is operated by the National Research Council of Canada, le Centre National de la Recherche Scientifique de France, and the University of Hawaii. Observations for the ESO 2.2-m telescope and the VLT were collected at the European Southern Observatory, Chile. Observations at the Palomar Observatory were made as part of a continuing collaborative agreement between the California Institute of Technology and Cornell University. Kitt Peak National Observatory, part of the National Optical Astronomy Observatories, is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation. The Nordic Optical Telescope is operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. We gratefully acknowledge financing from the French Research Ministry ACI Jeunes Chercheurs programme, the Institut National de Science de l'Univers, from the European Southern Observatory, from the NASA Planetary Astronomy programme and the Natural Sciences and Engineering Research Council of Canada.

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Correspondence to Brett Gladman.

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Gladman, B., Kavelaars, J., Holman, M. et al. Discovery of 12 satellites of Saturn exhibiting orbital clustering. Nature 412, 163–166 (2001). https://doi.org/10.1038/35084032

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