Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Discovery of 12 satellites of Saturn exhibiting orbital clustering


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.

This is a preview of subscription content, access via your institution

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

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


  1. Peale, S. J. Origin and evolution of the natural satellites. Annu. Rev. Astron. Astrophys. 37, 533–602 (1999).

    Article  Google Scholar 

  2. Gladman, B. J. et al. Discovery of two distant irregular moons of Uranus. Nature 392, 897–899 (1998).

    Article  CAS  Google Scholar 

  3. Gladman, B. J. et al. The discovery of Uranus XIX, XX, and XXI. Icarus 147, 320–324 (2000); erratum 148, 320 (2000).

    Article  Google Scholar 

  4. Marsden, B. G. S/1999 J 1. IAU Circ. 7460 (2000).

  5. Marsden, B. G. S/1975 J 1 = S/2000 J 1. IAU Circ. 7640 (2000).

  6. Green, D. Satellites of Jupiter. IAU Circ. 7555 (2001).

  7. Pollack, J. B., Burns, J. A. & Tauber, M. E. Gas drag in primordial circumplanetary envelopes: A mechanism for satellite capture. Icarus 37, 587–611 (1979).

    Article  Google Scholar 

  8. Colombo, G. & Franklin, F. A. On the formation of the outer satellite groups of Jupiter. Icarus 30, 186–189 (1971).

    Article  Google Scholar 

  9. Heppenheimer, T. A. & Porco, C. C. New contributions to the problem of capture. Icarus 30, 385–401 (1977).

    Article  Google Scholar 

  10. Saha, P. & Tremaine, S. The orbits of the retrograde jovian satellites. Icarus 106, 549–562 (1993).

    Article  Google Scholar 

  11. Hénon, M. Numerical exploration of the restricted problem. VI. Hill's case: Non-periodic orbits. Astron. Astrophys. 9, 24–36 (1970).

    MATH  Google Scholar 

  12. Hamilton, D. P. & Burns, J. A. Orbital stability zones about asteroids. Icarus 92, 118–131 (1991).

    Article  Google Scholar 

  13. Hamilton, D. P. & Krivov, A. V. Dynamics of distant moons of asteroids. Icarus 128, 241–249 (1997).

    Article  Google Scholar 

  14. Wiegert, P., Innanen, K. & Mikkola, S. The stability of quasi satellites in the outer solar system. Astron. J. 119, 1978–1984 (2000).

    Article  Google Scholar 

  15. Kozai, Y. Secular perturbations of asteroids with high inclination and eccentricity. Astron. J. 67, 591–598 (1962).

    Article  MathSciNet  Google Scholar 

  16. Kinoshita, H. & Nakai, H. Secular perturbations of fictitious satellites of Uranus. Celest. Mech. 52, 293–303 (1991).

    Article  Google Scholar 

  17. Clark, R. N., Fanale, F. P. & Gaffey, M. J. in Satellites (eds Burns, J. A. & Matthews, M. S.) 437–492 (Univ. Arizona Press, Tucson, 1986).

    Google Scholar 

  18. Luu, J. CCD photometry and spectroscopy of the outer jovian satellites. Astron. J. 102, 1213–1225 (1991).

    Article  Google Scholar 

  19. Jarvis, K. S. et al. JVI Himalia: New compositional evidence and interpretations for the origin of Jupiter's small satellites. Icarus 145, 445–453 (2000).

    Article  Google Scholar 

  20. Farinella, P. et al. The injection of asteroid fragments into resonances. Icarus 101, 174–187 (1993).

    Article  Google Scholar 

  21. Smith, B. A. et al. A new look at the Saturn system. Science 215, 504–537 (1982).

    Article  CAS  Google Scholar 

  22. Colwell, J. E. & Esposito, L. W. Origins of the rings of Uranus and Neptune. II. Initial distributions of disrupted satellite fragments. J. Geophys. Res. 98, 7387–7401 (1993).

    Article  Google Scholar 

  23. Porco, C. C. et al. in Neptune and Triton (ed. Cruikshank, D. P.) 703–804 (Univ. Arizona Press, Tucson, 1995).

    Google Scholar 

  24. Tanga, P. et al. On the size distribution of asteroid families: The role of geometry. Icarus 141, 65–78 (1999).

    Article  Google Scholar 

  25. Thomas, P. et al. Phoebe: Voyager 2 observations. J. Geophys. Res. 88, 8736–8742 (1986).

    Article  Google Scholar 

  26. Simonelli, D. et al. Phoebe: Albedo map and photometric properties. Icarus 138, 249–258 (1999).

    Article  Google Scholar 

  27. Gladman, B. et al. Pencil-beam surveys for faint trans-neptunian comets. Astron. J. 116, 2042–2054 (1998).

    Article  Google Scholar 

  28. McKinnon, W., Lunine, J. I. & Banfield, D. in Neptune and Triton (ed. Cruikshank, D. P.) 807–878 (Univ. Arizona Press, Tucson, 1995).

    Google Scholar 

  29. Marsden, B. G. S/2000 S 1 and S/2000 S 2. IAU Circ. 7512 (2000).

  30. Marsden, B. G. S/2000 S 3 and S/2000 S 4. IAU Circ. 7513 (2000).

  31. Marsden, B. G. S/2000 S 5 and S/2000 S 6. IAU Circ. 7521 (2000).

  32. Marsden, B. G. S/2000 S 7, S/2000 S 8 and S/2000 S9. IAU Circ. 7538 (2000).

  33. Marsden, B. G. S/2000 S 10. IAU Circ. 7539 (2000).

  34. Green, D. S/2000 S 11. IAU Circ. 7545 (2000).

  35. Green, D. S/2000 S 12. IAU Circ. 7548 (2000).

Download references


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.

Author information

Authors and Affiliations


Corresponding author

Correspondence to Brett Gladman.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Gladman, B., Kavelaars, J., Holman, M. et al. Discovery of 12 satellites of Saturn exhibiting orbital clustering. Nature 412, 163–166 (2001).

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing