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.

  • Letter
  • Published:

A rigid and weathered ice shell on Titan



Several lines of evidence suggest that Saturn’s largest moon, Titan, has a global subsurface ocean beneath an outer ice shell 50 to 200 kilometres thick1,2,3,4. If convection5,6 is occurring, the rigid portion of the shell is expected to be thin; similarly, a weak, isostatically compensated shell has been proposed7,8 to explain the observed topography. Here we report a strong inverse correlation between gravity3 and topography9 at long wavelengths that are not dominated by tides and rotation. We argue that negative gravity anomalies (mass deficits) produced by crustal thickening at the base of the ice shell overwhelm positive gravity anomalies (mass excesses) produced by the small surface topography, giving rise to this inverse correlation. We show that this situation requires a substantially rigid ice shell with an elastic thickness exceeding 40 kilometres, and hundreds of metres of surface erosion and deposition, consistent with recent estimates from local features10,11. Our results are therefore not compatible with a geologically active, low-rigidity ice shell. After extrapolating to wavelengths that are controlled by tides and rotation, we suggest that Titan’s moment of inertia may be even higher (that is, Titan may be even less centrally condensed) than is currently thought12.

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

Access options

Buy this article

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

Figure 1: Titan’s degree-3 gravity and topography.
Figure 2: Admittance estimates for nine sets of gravity and topography data.
Figure 3: Model predictions of admittance and erosion.

Similar content being viewed by others


  1. Béghin, C., Sotin, C. & Hamelin, M. Titan’s native ocean revealed beneath some 45 km of ice by a Schumann-like resonance. C. R. Geosci. 342, 425–433 (2010)

    Article  Google Scholar 

  2. Bills, B. G. & Nimmo, F. Rotational dynamics and internal structure of Titan. Icarus 214, 351–355 (2011)

    Article  ADS  Google Scholar 

  3. Iess, L. et al. The tides of Titan. Science 337, 457–459 (2012)

    Article  ADS  CAS  Google Scholar 

  4. Tobie, G., Lunine, J. I. & Sotin, C. Episodic outgassing as the origin of atmospheric methane on Titan. Nature 440, 61–64 (2006)

    Article  ADS  CAS  Google Scholar 

  5. Mitri, G. & Showman, A. P. Thermal convection in ice-I shells of Titan and Enceladus. Icarus 193, 387–396 (2008)

    Article  ADS  CAS  Google Scholar 

  6. Tobie, G., Grasset, O., Lunine, J. I., Mocquet, A. & Sotin, C. Titan’s internal structure inferred from a coupled thermal-orbital model. Icarus 175, 496–502 (2005)

    Article  ADS  CAS  Google Scholar 

  7. Nimmo, F. & Bills, B. G. Shell thickness variations and the long-wavelength topography of Titan. Icarus 208, 896–904 (2010)

    Article  ADS  Google Scholar 

  8. Choukroun, M. & Sotin, C. Is Titan’s shape caused by its meteorology and carbon cycle? Geophys. Res. Lett. 39, 1–5 (2012)

    Article  Google Scholar 

  9. Zebker, H. A. et al. Titan’s figure fatter, flatter than its gravity field. AGU Fall Meet. abstr. P23F–01. (2012)

  10. Neish, C. D. et al. Crater topography on Titan: implications for landscape evolution. Icarus 223, 82–90 (2013)

    Article  ADS  Google Scholar 

  11. Moore, J. M., Howard, A. D. & Schenk, P. M. Bedrock denudation on Titan: estimates of vertical extent and lateral debris dispersion. Lunar Planet. Sci. Conf. XXXXIIII, abstr. 1763. (2013)

  12. Iess, L. et al. Gravity field, shape, and moment of inertia of Titan. Science 327, 1367–1369 (2010)

    Article  ADS  CAS  Google Scholar 

  13. Stiles, B. W. et al. Determining Titan surface topography from Cassini SAR data. Icarus 202, 584–598 (2009)

    Article  ADS  Google Scholar 

  14. Zebker, H. et al. Size and shape of Saturn’s moon Titan. Science 324, 921–923 (2009)

    Article  ADS  CAS  Google Scholar 

  15. McKenzie, D. The relationship between topography and gravity on Earth and Venus. Icarus 112, 55–88 (1994)

    Article  ADS  Google Scholar 

  16. Wieczorek, M. A. Gravity and topography of the terrestrial planets. Treat. Geophys. 10, 165–206 (2007)

    Article  Google Scholar 

  17. Richards, M. A. & Hager, B. H. Geoid anomalies in a dynamic Earth. J. Geophys. Res. 89, 5987–6002 (1984)

    Article  ADS  Google Scholar 

  18. Roberts, J. H. & Nimmo, F. Tidal heating and the long-term stability of a subsurface ocean on Enceladus. Icarus 194, 675–689 (2008)

    Article  ADS  Google Scholar 

  19. Kraus, H. Thin Elastic Shells (Wiley, 1967)

    MATH  Google Scholar 

  20. Turcotte, D. L., Willemann, R. J., Haxby, W. F. & Norberry, J. Role of membrane stresses in the support of planetary topography. J. Geophys. Res. 86, 3951–3959 (1981)

    Article  ADS  Google Scholar 

  21. McGovern, P. J. et al. Localized gravity/topography admittance and correlation spectra on Mars: implications for regional and global evolution. J. Geophys. Res. 107 5136 (2002)

  22. Moore, J. M. & Pappalardo, R. T. Titan: an exogenic world? Icarus 212, 790–806 (2011)

    Article  ADS  Google Scholar 

  23. Grasset, O., Sotin, C. & Deschamps, F. On the internal structure and dynamics of Titan. Planet. Space Sci. 48, 617–636 (2000)

    Article  ADS  CAS  Google Scholar 

  24. Lopes, R. M. C. et al. Cryovolcanic features on Titan’s surface as revealed by the Cassini Titan Radar Mapper. Icarus 186, 395–412 (2007)

    Article  ADS  Google Scholar 

  25. Běhounková, M., Tobie, G., Choblet, G. & Čadek, O. Tidally-induced melting events as the origin of south-pole activity on Enceladus. Icarus 219, 655–664 (2012)

    Article  ADS  Google Scholar 

  26. Nimmo, F. Non-Newtonian topographic relaxation on Europa. Icarus 168, 205–208 (2004)

    Article  ADS  CAS  Google Scholar 

  27. Black, B. A., Perron, J. T., Burr, D. M. & Drummond, S. A. Estimating erosional exhumation on Titan from drainage network morphology. J. Geophys. Res. 117 E08006 (2012)

  28. Patterson, D. B., Farley, K. A. & Norman, M. D. He-4 as a tracer of continental dust: a 1.9 million year record of aeolian flux to the west equatorial Pacific Ocean. Geochim. Cosmochim. Acta 63, 615–625 (1999)

    Article  ADS  CAS  Google Scholar 

  29. O’Rourke, J. G. & Stevenson, D. J. Stability of ice/rock mixtures with applications to Titan. Lunar Planet. Sci. Conf. XXXXII, abstr. 1629 (2011)

Download references


We thank the Cassini radar science team, M. Manga, D. Stevenson, R. Pappalardo and W. McKinnon for their suggestions. Portions of this work were supported by NASA grants NNX13AG02G and NNX11AK44G.

Author information

Authors and Affiliations



F.N. initiated the effort. D.H. and F.N. developed the loading models and analysed the results. L.I. led the development of the gravity field models. H.Z. synthesized the topography models. All authors discussed the results and implications and commented on the manuscript.

Corresponding author

Correspondence to D. Hemingway.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Text and Data, Supplementary Figures 1-11, Supplementary Tables 1-4 and Supplementary References. (PDF 1639 kb)

PowerPoint slides

Rights and permissions

Reprints and permissions

About this article

Cite this article

Hemingway, D., Nimmo, F., Zebker, H. et al. A rigid and weathered ice shell on Titan. Nature 500, 550–552 (2013).

Download citation

  • Received:

  • Accepted:

  • Published:

  • 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