Article | Published:

Deep and methane-rich lakes on Titan

Abstract

Saturn’s largest moon, Titan, hosts liquid hydrocarbon lakes and seas on its surface. During the last close encounter with Titan (22 April 2017), the Cassini spacecraft used its RADAR as a sounder to probe the depth of several lakes in the north polar terrain. This was the first time that Titan’s lakes, as opposed to its seas, have been viewed in a sounding configuration. Here, we show that these lakes can exceed 100 m depth and their transparency at the 2.17 cm radar wavelength indicates that they have a methane-dominated composition. This composition differs significantly from that of Ontario Lacus, the only major lake in Titan’s southern hemisphere, which is more ethane rich. If the methane-rich north polar lakes, perched hundreds of metres above the major seas, are formed by a karstic-type process, then they may drain by subsurface flow at rates between 0.001 and 1 m yr−1 (Titan year). Subsurface reservoirs and flows therefore may be an important element of the Titan geochemical system.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request. Long Burst Data Record products are available from NASA Planetary Data System (https://pds-imaging.jpl.nasa.gov/data/cassini/cassini_orbiter).

Additional information

Journal peer review information: Nature Astronomy thanks Alice Le Gall and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

References

  1. 1.

    Elachi, C. et al. Radar: the Cassini Titan radar mapper. Space Sci. Rev. 115, 71–110 (2004).

  2. 2.

    Stofan, E. R. et al. The lakes of Titan. Nature 445, 61–64 (2007).

  3. 3.

    Hayes, A. G. et al. Hydrocarbon lakes on Titan: distribution and interaction with a porous regolith. Geophys. Res. Lett. 35, L09204 (2008).

  4. 4.

    Hayes, A. G. The lakes and seas of titan. Annu. Rev. Earth Space Sci. 44, 57–83 (2016).

  5. 5.

    Hayes, A. G., Lorenz, R. D. & Lunine, J. I. A post Cassini view of Titan’s methane-based hydrologic cycle. Nat. Geosci. 11, 306–313 (2018).

  6. 6.

    Corlies, P. et al. Titan’s topography and shape at the end of the Cassini mission. Geophys. Res. Lett. 44, 11754–11761 (2017).

  7. 7.

    Hayes, A. G. et al. Topographic constraints on the evolution and connectivity of Titan’s lacustrine basins. Geophys. Res. Lett. 44, 11745–11753 (2017).

  8. 8.

    Birch, S. P. D. et al. Geomorphologic mapping of titan’s polar terrains: Constraining surface processes and landscape evolution. Icarus 282, 214–236 (2017).

  9. 9.

    Cornet, T. et al. Dissolution on titan and on Earth: toward the age of Titan’s karstic landscapes. J. Geophys. Res. Planets 120, 1044–1074 (2015).

  10. 10.

    Mastrogiuseppe, M. et al. The bathymetry of a Titan sea. Geophys. Res. Lett. 41, 1432–1437 (2014).

  11. 11.

    Mastrogiuseppe, M. et al. Radar sounding using the Cassini altimeter: waveform modeling and Monte Carlo approach for data inversion of observations of Titan’s seas. IEEE Trans. Geosci. Remote Sens. 54, 5646–5656 (2016).

  12. 12.

    Mastrogiuseppe, M. et al. Bathymetry and composition of Titan’s Ontario Lacus derived from Monte Carlo-based waveform inversion of Cassini RADAR altimetry data. Icarus 300, 203–209 (2018).

  13. 13.

    Mastrogiuseppe, M. et al. Cassini radar observation of Punga Mare and environs: bathymetry and composition. Earth Planet. Sci. Lett. 496, 89–95 (2018).

  14. 14.

    Alberti, G. et al. The processing of altimetric data (PAD) system for Cassini RADAR. Mem. Soc. Astron. Ital. Suppl. 11, 68 (2007).

  15. 15.

    Raguso, M. C., Mastrogiuseppe, M., Seu, R. & Piazzo, L. Super resolution and interferences suppression technique applied to SHARAD data. In 5th IEEE Int. Workshop Metrology for AeroSpace 242–246 (IEEE, 2018).

  16. 16.

    Mitchell, K. L., Barmatz, M. B., Jamieson, C. S., Lorenz, R. D. & Lunine, J. I. Laboratory measurements of cryogenic liquid alkane microwave absorptivity and implications for the composition of Ligeia Mare, Titan. Geophys. Res. Lett. 42, 1340–1345 (2015).

  17. 17.

    Poggiali, V. et al. Liquid-filled canyons on Titan. Geophys. Res. Lett. 43, 7887–7894 (2016).

  18. 18.

    Zebker, H. et al. Surface of Ligeia Mare, Titan, from Cassini altimeter and radiometer analysis. Geophys. Res. Lett. 41, 308–313 (2014).

  19. 19.

    Grima, C. et al. Surface roughness of Titan’s hydrocarbon seas. Earth Planet. Sci. Lett. 474, 20–24 (2017).

  20. 20.

    Hayes, A. G. et al. Transient surface liquid in Titan’s polar regions from cassini. Icarus 211, 655–671 (2011).

  21. 21.

    Hofgartner, J. D. et al. Titan’s "magic islands": transient features in a hydrocarbon sea. Icarus 271, 338–349 (2016).

  22. 22.

    Le Gall, A. et al. Composition, seasonal change and bathymetry of Ligeia Mare, Titan, derived from its microwave thermal emission. J. Geophys. Res. Planets 121, 233–251 (2016).

  23. 23.

    Janssen, M. A. et al. Titan’s surface at 2.18-cm wavelength imaged by the Cassini RADAR radiometer: results and interpretations through the first ten years of observation. Icarus 270, 443–459 (2016).

  24. 24.

    Turtle, E. P. et al. Titan’s meteorology over the Cassini mission: evidence for extensive subsurface methane reservoirs. Geophys. Res. Lett. 45, 5320–5328 (2018).

  25. 25.

    Aharonson, O. et al. An asymmetric distribution of lakes on Titan as a possible consequence of orbital forcing. Nat. Geosci. 2, 851–854 (2009).

  26. 26.

    Dhingra, R. D. et al. Observational evidence for summer rainfall at Titan’s north pole. Geophys. Res. Lett. 46, 1205–1212 (2019).

  27. 27.

    Cordier, D. et al. Structure of Titan’s evaporites. Icarus 270, 41–56 (2016).

  28. 28.

    MacKenzie, S. M. & Barnes, J. W. Compositional similarities and distinctions between Titan’s evaporitic terrains. Astrophys. J. 821, 17 (2016).

  29. 29.

    Mitchell, K. L., Malaska, M. J., Horvath, D. G. & Andrews-Hanna, J. C. Karstic processes on Earth and Titan. In 45th Lunar Planet. Sci. Conf. 2371 (LPI, 2008).

  30. 30.

    Lorenz, R. D. & Lunine, J. I. Erosion on Titan: past and present. Icarus 122, 79–91 (1996).

  31. 31.

    Malaska, M. J. & Hodyss, R. Dissolution of benzene, naphthalene, and biphenyl in a simulated Titan lake. Icarus 242, 74–81 (2014).

  32. 32.

    Glein, C. R. & Shock, E. L. A geochemical model of non-ideal solutions in the methane–ethane–propane–nitrogen–acetylene system on Titan. Geochim. Cosmochim. Acta 115, 217–240 (2013).

  33. 33.

    Lorenz, R. D. The flushing of Ligeia: composition variations across Titan’s seas in a simple hydrological model. Geophys. Res. Lett. 41, 5764–5770 (2014).

  34. 34.

    Choukroun, M. & Sotin, C. Is Titan’s shape caused by its meteorology and carbon cycle? Geophys. Res. Lett. 39, L04201 (2012).

  35. 35.

    Alberti, G., Festa, L., Papa, C. & Vingione, G. A waveform model for near-nadir radar altimetry applied to the Cassini mission to Titan. IEEE Trans. Geosci. Remote Sens. 47, 2252–2261 (2009).

  36. 36.

    Bucciarelli, T. et al. Tracking algorithms in radar altimetry. In Int. Geosci. Remote Sensing Symp. (IGARSS’88) Vol. 2, 973–976 (IEEE, 1988).

  37. 37.

    Mastrogiuseppe, M. et al. Titan dune heights retrieval by using Cassini radar altimeter. Icarus 230, 336–354 (2014).

  38. 38.

    Born, M. & Wolf, E. Principles of Optics: Electromagnetic Theory of Propagation, Interference and Diffraction of Light 7th edn (Cambridge Univ. Press, Cambridge, 1999).

  39. 39.

    Zhang, Z. et al. Dielectric properties of the Martian south polar layered deposits: MARSIS data inversion using Bayesian inference and genetic algorithm. J. Geophys. Res. Planets 113, 5004 (2008).

  40. 40.

    Fung, A. K. & Eom, H. J. Coherent scattering of a spherical wave from an irregular surface. IEEE Trans. Antennas Propag. 31, 68–72 (1983).

  41. 41.

    Picardi, G., Seu, R., Coradini, A., Zampolini, E. & Ciaffone, A. The radar system for the exploration of Titan. Il Nuovo Cimento C 15, 1149–1161 (1992).

Download references

Acknowledgements

M.M. and R.S. acknowledge support from Italian Space Agency (ASI) grant 2014-041-R.0.; M.M., A.G.H. and V.P. acknowledge support from NASA CDAP grant NNX15AH10G; J.I.L. is grateful for the ministrations of the Cassini mission in supporting his research. R.L. acknowledges the support of NASA OPR Grant NNX13AK97G. We appreciate the efforts of the Cassini TOST (Titan Orbiter Science Team) and RADAR Team in planning and executing these observations.

Author information

M.M. led the data analysis, conceived the main conceptual ideas and wrote the manuscript. V.P. made a significant contribution to the analysis and interpretation of data, performed some of the numerical calculations, contributed to the writing of the manuscript and prepared figures. J.I.L. participated in the calculations of the lake compositions and co-wrote the interpretation in terms of geological mechanisms. A.G.H. and R.L. participated in the interpretation of geological mechanism, contributed to drafting the article and revising it for intellectual content. R.S. and G.M. contributed to data analysis and interpretation and contributed to drafting the article.

Competing interests

The authors declare no competing interests.

Correspondence to M. Mastrogiuseppe.

Supplementary information

  1. Supplementary Information

    Supplementary Figures 1–2, Supplementary Table 1

Rights and permissions

To obtain permission to re-use content from this article visit RightsLink.

About this article

Further reading

Fig. 1: Cassini RADAR image mosaic and altimetry tracks acquired during the Cassini mission on the norther polar region of Titan.
Fig. 2: Intercepted lakes from radar altimetry on T126 flyby.
Fig. 3: Bathymetry and liquid attenuation of Winnipeg Lacus.
Fig. 4: Ambiguous lakefloor detections of Oneida Lacus and lake C.
Fig. 5: Comparison of Ligeia Mare and lake surface backscattering during flyby T91 (23 May 2013) and T126 (22 April 2017).
Fig. 6: Ligeia Mare and Winnipeg Lacus waveforms acquired at similar depths.