Article

The seasonal cycle of Titan's detached haze

Received:
Accepted:
Published online:

Abstract

Titan's ‘detached’ haze, seen in Voyager images in 1980 and 1981 and monitored by the Cassini Imaging Science Subsystem (ISS) during the period 2004–2017, provides a measure of seasonal activity in Titan’s mesosphere with observations over almost half of Saturn’s seasonal cycle. Here we report on retrieved haze extinction profiles that reveal a depleted layer (having a diminished aerosol content), visually manifested as a gap between the main haze and a thin, detached upper layer. Our measurements show the disappearance of the feature in 2012 and its reappearance in 2016, as well as details after the reappearance. These observations highlight the dynamical nature of the detached haze. The reappearance seems congruent with earlier descriptions by climate models but more complex than previously described. It occurs in two steps, first as haze reappearing at 450 ± 20 km and one year later at 510 ± 20 km. These observations provide additional tight and valuable constraints about the underlying mechanisms, especially for Titan's mesosphere, that control Titan's haze cycle.

  • Subscribe to Nature Astronomy for full access:

    $99

    Subscribe

Additional access options:

Already a subscriber?  Log in  now or  Register  for online access.

Additional information

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

References

  1. 1.

    Smith, B. A. et al. Encounter with Saturn: Voyager 1 Imaging Science Results. Science 212, 163–191 (1981).

  2. 2.

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

  3. 3.

    Sromovsky, L. A. et al. Implications of Titan’s north–south brightness asymmetry. Nature 292, 698–702 (1981).

  4. 4.

    Rages, K. & Pollack, J. Vertical distribution of scattering hazes in Titan’s upper atmosphere. Icarus 55, 50–62 (1983).

  5. 5.

    Toon, O. B., McKay, C. P., Griffith, C. A. & Turco, R. P. A physical model of Titan aerosols. Icarus 95, 24–53 (1992).

  6. 6.

    Rannou, P., Hourdin, F. & McKay, C. P. A wind origin for Titan’s haze structure. Nature 418, 853–856 (2002).

  7. 7.

    Chassefière, E. & Cabane, M. Two formation regions for Titan’s hazes: indirect clues and possible synthesis mechanisms. Planet. Space Sci. 43, 91–103 (1995).

  8. 8.

    Lavvas, P., Yelle, R. V. & Vuitton, V. The detached haze layer in Titan’s mesosphere. Icarus 201, 626–633 (2009).

  9. 9.

    Porco, C. C. et al. Imaging of Titan from the Cassini spacecraft. Nature 434, 159–168 (2005).

  10. 10.

    Seignovert, B., Rannou, P., Lavvas, P., Cours, T. & West, R. A. Aerosol optical properties in Titan’s detached haze layer before the equinox. Icarus 292, 13–21 (2017).

  11. 11.

    West, R. A. et al. The evolution of Titan’s detached haze layer near equinox in 2009. Geophys. Res. Lett. 38, L06204 (2011).

  12. 12.

    Lebonnois, S., Burgalat, J., Rannou, P. & Charnay, B. Titan global climate model: a new 3-dimensional version of the IPSL Titan GCM. Icarus 218, 707–722 (2012).

  13. 13.

    Larson, E. J. L., Toon, O. B., West, R. A. & Friedson, A. J. Microphysical modeling of Titan’s detached haze layer in a 3D GCM. Icarus 254, 122–134 (2015).

  14. 14.

    Rannou, P., Cabane, M., Botet, R. & Chassefière, E. A new interpretation of scattered light measurements at Titan’s Limb. J. Geophys. Res. E Planets 102, 10997–11013 (1997).

  15. 15.

    West, R. A. et al. Cassini Imaging Science Subsystem observations of Titan’s south polar cloud. Icarus 270, 399–408 (2016).

  16. 16.

    Vinatier, S. et al. Seasonal variations in Titan’s stratosphere observed with Cassini/CIRS after the northern spring equinox. Am. Astron. Soc. DPS Meeting 48, abstract id.509.09. (2016).

  17. 17.

    Rannou, P., Hourdin, F., McKay, C. P. & Luz, D. A coupled dynamics–microphysics model of Titan’s atmosphere. Icarus 170, 443–462 (2004).

  18. 18.

    Cours, T. et al. Dual origin of aerosols in Titan’s detached haze layer. Astrophys. J. Lett. 741, L32 (2011).

  19. 19.

    Lavvas, P., Sander, M., Kraft, M. & Imanaka, H. Surface chemistry and particle shape: processes on the evolution of aerosols in Titan’s atmosphere. Astrophys. J. 728, 80 (2011).

  20. 20.

    Koskinen, T. et al. The mesosphere and lower thermosphere of Titan revealed by Cassini/UVIS stellar occultations. Icarus 216, 507–534 (2011).

  21. 21.

    Lavvas, P. et al. Aerosol properties in Titan’s upper atmosphere. Proc. Titan Aeronomy and Climate Workshop http://adsabs.harvard.edu/abs/2016tac.confE.29L (2016).

  22. 22.

    Sicardy, B. et al. The two Titan stellar occultations of 14 November 2003. J. Geoph. Res. 111, E11S91 (2006).

  23. 23.

    Fulchignoni, M. et al. In situ measurements of the physical characteristics of Titan’s environment. Nature 438, 785–791 (2005).

  24. 24.

    Sicardy, B. et al. The structure of Titan’s stratosphere from the 28 Sgr occultation. Icarus 142, 357–390 (1999).

  25. 25.

    Cabane, M., Chassefière, E. & Israel, G. Formation and growth of photochemical aerosols in Titan’s atmosphere. Icarus 96, 176–189 (1993).

  26. 26.

    Fuchs, N. Mechanics of Aerosols (Pergamon, London, 1964).

  27. 27.

    Larson, E. J. L., Toon, O. B. & Friedson, A. J. Simulating Titan’s aerosols in a three-dimensional general circulation model. Icarus 243, 400 (2014).

Download references

Acknowledgements

Research was supported by the Cassini-Huygens mission, a cooperative endeavour of NASA, ESA and ASI managed by JPL/Caltech under a contract with NASA. Part of this work was performed by the Jet Propulsion Laboratory, California Institute of Technology. Part of this work was done while R.A.W. was hosted at the Université de Reims Champagne-Ardenne with the support of the Région Champagne-Ardenne, and simultaneously with the support of the JPL Senior Research Scientist Leave programme. P.R. thanks the Agence Nationale de la Recherche (ANR Project ‘APOSTIC’ no. 11BS56002, France).

Author information

Affiliations

  1. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

    • Robert A. West
    • , Philip Dumont
    • , Mou Roy
    •  & Aida Ovanessian
  2. GSMA, UMR CNRS 7331, Université de Reims Champagne-Ardenne, Reims, France

    • Robert A. West
    • , Benoît Seignovert
    •  & Pascal Rannou
  3. Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA

    • Elizabeth P. Turtle
  4. Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA

    • Jason Perry

Authors

  1. Search for Robert A. West in:

  2. Search for Benoît Seignovert in:

  3. Search for Pascal Rannou in:

  4. Search for Philip Dumont in:

  5. Search for Elizabeth P. Turtle in:

  6. Search for Jason Perry in:

  7. Search for Mou Roy in:

  8. Search for Aida Ovanessian in:

Contributions

R.A.W. contributed original data and measurements. B.S. contributed measurements and figures. P.R. contributed aerosol retrievals and discussion of haze and climate models. P.D. assisted with scattering models. E.P.T., J.P. and M.R. assisted with data acquisition. A.O. assisted with measurements.

Competing interests

The authors declare no competing interests.

Corresponding author

Correspondence to Robert A. West.

Supplementary information

  1. Supplementary Information

    Supplementary Figures 1–3