Skip to main content

Thank you for visiting nature.com. 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.

  • Letter
  • Published:

100-metre-diameter moonlets in Saturn's A ring from observations of 'propeller' structures

Nature volume 440, pages 648–650 (2006)Cite this article

Abstract

Saturn's main rings are composed predominantly of water-ice particles ranging between about 1 centimetre and 10 metres in radius. Above this size range, the number of particles drops sharply, according to the interpretation of spacecraft1 and stellar2 occultations. Other than the gap moons Pan and Daphnis (the provisional name of S/2005 S1), which have sizes of several kilometres, no individual bodies in the rings have been directly observed, and the population of ring particles larger than ten metres has been essentially unknown. Here we report the observation of four longitudinal double-streaks in an otherwise bland part of the mid-A ring. We infer that these ‘propeller’-shaped perturbations3,4,5 arise from the effects of embedded moonlets approximately 40 to 120 m in diameter. Direct observation of this phenomenon validates models of proto-planetary disks in which similar processes are posited4,6. A population of moonlets, as implied by the size distribution that we find, could help explain gaps in the more tenuous regions of the Cassini division and the C ring7. The existence of such large embedded moonlets is most naturally compatible with a ring originating in the break-up of a larger body8,9,10,11, but accretion from a circumplanetary disk12 is also plausible if subsequent growth onto large particles occurs after the primary accretion phase has concluded13,14.

Access through your institution
Buy or subscribe

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

Access options

Access through your institution

Buy this article

  • Purchase on SpringerLink
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Four longitudinally aligned double-streaks observed in a bland region of Saturn's A ring by the Cassini ISS camera.
Figure 2: Peak locations and longitudinal scans of the four double-streaks in Fig. 1.
Figure 3: Cumulative size distribution for particles in the A ring.

Similar content being viewed by others

References

  1. Zebker, H. A., Marouf, E. A. & Tyler, G. L. Saturn's rings: Particle size distributions for thin layer models. Icarus 64, 531–548 (1985)

    Article  ADS  Google Scholar 

  2. French, R. G. & Nicholson, P. D. Saturn's rings II. Particle sizes inferred from stellar occultation data. Icarus 145, 502–523 (2000)

    Article  ADS  Google Scholar 

  3. Spahn, F. & Sremcevic, M. Density patterns induced by small moonlets in Saturn's rings? Astron. Astrophys. 358, 368–372 (2000)

    ADS  Google Scholar 

  4. Sremcevic, M., Spahn, F. & Duschl, W. J. Density structures in perturbed thin cold discs. Mon. Not. R. Astron. Soc. 337, 1139–1152 (2002)

    Article  ADS  Google Scholar 

  5. Seiss, M., Spahn, F., Sremcevic, M. & Salo, H. Structures induced by small moonlets in Saturn's rings: Implications for the Cassini Mission. Geophys. Res. Lett. 32, L11205, doi:10.1029/2005GL022506 (2005)

    Article  ADS  Google Scholar 

  6. Bryden, G., Chen, X., Lin, D. N. C., Nelson, R. P. & Papaloizou, J. C. B. Tidally induced gap formation in protostellar disks: gap clearing and suppression of protoplanetary growth. Astrophys. J. 514, 344–367 (1999)

    Article  ADS  Google Scholar 

  7. Lissauer, J. J., Shu, F. H. & Cuzzi, J. N. Moonlets in Saturn's rings? Nature 292, 707–711 (1981)

    Article  ADS  Google Scholar 

  8. Harris, A. W. in Planetary Rings (eds Greenberg, R. & Brahic, A.) 641–659 (Univ. Arizona Press, Tucson, 1984)

    Google Scholar 

  9. Dones, L. A recent cometary origin for Saturn's rings? Icarus 92, 194–203 (1991)

    Article  ADS  Google Scholar 

  10. Smith, B. A. et al. A new look at the Saturn system—the Voyager 2 images. Science 215, 504–537 (1982)

    Article  CAS  ADS  Google Scholar 

  11. Colwell, J. E. The disruption of planetary satellites and the creation of planetary rings. Planet. Space Sci. 42, 1139–1149 (1994)

    Article  ADS  Google Scholar 

  12. Pollack, J. B. The rings of Saturn. Space Sci. Rev. 18, 3–93 (1975)

    Article  ADS  Google Scholar 

  13. Shu, F. H. in Planetary Rings (eds Greenberg, R. & Brahic, A.) 513–561 (Univ. Arizona Press, Tucson, 1984)

    Google Scholar 

  14. Weidenschilling, S. J., Chapman, C. R., Davis, D. & Greenberg, R. in Planetary Rings (eds Greenberg, R. & Brahic, A.) 367–415 (Univ. Arizona Press, Tucson, 1984)

    Google Scholar 

  15. Julian, W. H. & Toomre, A. Non-axisymmetric responses of differentially rotating disks of stars. Astrophys. J. 146, 810–827 (1966)

    Article  ADS  Google Scholar 

  16. Murray, C. D. & Dermott, S. F. Solar System Dynamics (Cambridge Univ. Press, 1999)

    MATH  Google Scholar 

  17. Hénon, M. A simple model of Saturn's rings. Nature 293, 33–35 (1981)

    Article  ADS  Google Scholar 

  18. Showalter, M. R., Cuzzi, J. N., Marouf, E. A. & Esposito, L. W. Satellite ‘wakes’ and the orbit of the Encke Gap moonlet. Icarus 66, 297–323 (1986)

    Article  ADS  Google Scholar 

  19. Porco, C. C. et al. Cassini Imaging Science: initial results on Saturn's rings and small satellites. Science 307, 1226–1236 (2005)

    Article  CAS  ADS  Google Scholar 

  20. Lewis, M. C. & Stewart, G. R. Expectations for Cassini observations of ring material with nearby moons. Icarus 178, 124–143 (2005)

    Article  ADS  Google Scholar 

  21. Esposito, L. A., O'Callahan, M. & West, R. A. The structure of Saturn's rings: Implications from the Voyager stellar occultation. Icarus 56, 439–452 (1983)

    Article  ADS  Google Scholar 

  22. Nicholson, P. D. et al. Saturn's rings I. Optical depth profiles from the 28 Sgr occultation. Icarus 145, 474–501 (2000)

    Article  ADS  Google Scholar 

  23. Cuzzi, J. N. et al. in Planetary Rings (eds Greenberg, R. & Brahic, A.) 73–199 (Univ. Arizona Press, Tucson, 1984)

    Google Scholar 

  24. Dones, L., Cuzzi, J. N. & Showalter, M. R. Voyager photometry of Saturn's A ring. Icarus 105, 184–215 (1993)

    Article  ADS  Google Scholar 

  25. Dones, L. & Porco, C. C. Spiral density wakes in Saturn's A Ring? Bull. Am. Astron. Soc. 21, 929 (1989)

    ADS  Google Scholar 

  26. Salo, H. Simulations of dense planetary rings III. Self-gravitating identical particles. Icarus 117, 287–312 (1995)

    Article  ADS  Google Scholar 

  27. Karjalainen, R. & Salo, H. Gravitational accretion of particles in Saturn's rings. Icarus 172, 328–348 (2004)

    Article  ADS  Google Scholar 

  28. Daisaka, H., Tanaka, H. & Ida, S. Viscosity in a dense planetary ring with self-gravitating particles. Icarus 154, 296–312 (2001)

    Article  ADS  Google Scholar 

  29. Showalter, M. R. & Nicholson, P. D. Saturn's rings through a microscope—particle size constraints from the Voyager PPS scan. Icarus 87, 285–306 (1990)

    Article  ADS  Google Scholar 

  30. Porco, C. C. et al. Cassini Imaging Science: instrument characteristics and anticipated scientific investigations at Saturn. Space Sci. Rev. 115, 363–497 (2004)

    Article  ADS  Google Scholar 

Download references

Acknowledgements

We thank E. Baker for help with data reduction, and P. Nicholson for discussions. We acknowledge support from JPL, the Cassini project, NASA's Planetary Geology and Geophysics program, and the UK Particle Physics and Astronomy Research Council.

Author information

Authors and Affiliations

  1. Department of Astronomy, Cornell University,

    Matthew S. Tiscareno, Joseph A. Burns & Matthew M. Hedman

  2. Department of Theoretical and Applied Mechanics, Cornell University, New York, 14853, Ithaca, USA

    Joseph A. Burns

  3. CICLOPS, Space Science Institute, 4750 Walnut Street, Colorado, 80301, Boulder, USA

    Carolyn C. Porco & John W. Weiss

  4. Southwest Research Institute, 1050 Walnut Street, Colorado, 80302, Boulder, USA

    Luke Dones

  5. Department of Astronomy, University of Maryland, Maryland, 20742, College Park, USA

    Derek C. Richardson

  6. Astronomy Unit, Queen Mary, University of London, Mile End Road, E1 4NS, UK

    Carl D. Murray

Authors
  1. Matthew S. Tiscareno
    View author publications

    You can also search for this author inPubMed Google Scholar

  2. Joseph A. Burns
    View author publications

    You can also search for this author inPubMed Google Scholar

  3. Matthew M. Hedman
    View author publications

    You can also search for this author inPubMed Google Scholar

  4. Carolyn C. Porco
    View author publications

    You can also search for this author inPubMed Google Scholar

  5. John W. Weiss
    View author publications

    You can also search for this author inPubMed Google Scholar

  6. Luke Dones
    View author publications

    You can also search for this author inPubMed Google Scholar

  7. Derek C. Richardson
    View author publications

    You can also search for this author inPubMed Google Scholar

  8. Carl D. Murray
    View author publications

    You can also search for this author inPubMed Google Scholar

Corresponding author

Correspondence to Matthew S. Tiscareno.

Ethics declarations

Competing interests

Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.

Supplementary information

Supplementary Figures

This file contains Supplementary Figures 1–4 and their legends. (PDF 2642 kb)

Rights and permissions

Reprints and permissions

About this article

Cite this article

Tiscareno, M., Burns, J., Hedman, M. et al. 100-metre-diameter moonlets in Saturn's A ring from observations of 'propeller' structures. Nature 440, 648–650 (2006). https://doi.org/10.1038/nature04581

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nature04581

Search

Advanced search

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