Article | Published:

The evolution of Titan’s high-altitude aerosols under ultraviolet irradiation

Nature Astronomyvolume 2pages489494 (2018) | Download Citation


The Cassini–Huygens space mission revealed that Titan’s thick brownish haze is initiated high in the atmosphere at an altitude of about 1,000 km, before a slow transportation down to the surface. Close to the surface, at altitudes below 130 km, the Huygens probe provided information on the chemical composition of the haze. So far, we have not had insights into the possible photochemical evolution of the aerosols making up the haze during their descent. Here, we address this atmospheric aerosol aging process, simulating in the laboratory how solar vacuum ultraviolet irradiation affects the aerosol optical properties as probed by infrared spectroscopy. An important evolution was found that could explain the apparent contradiction between the nitrogen-poor infrared spectroscopic signature observed by Cassini below 600 km of altitude in Titan’s atmosphere and a high nitrogen content as measured by the aerosol collector and pyrolyser of the Huygens probe at the surface of Titan.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Additional information

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


  1. 1.

    Niemann, H. B. et al. The abundances of constituents of Titan’s atmosphere from the GCMS instrument on the Huygens probe. Nature 438, 779–784 (2005).

  2. 2.

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

  3. 3.

    Lavvas, P. et al. Aerosol growth in Titan’s ionosphere. Proc. Natl Acad. Sci. USA 110, 2729–2734 (2013).

  4. 4.

    Waite, J. H. Jr et al. The process of tholin formation in Titan’s upper atmosphere. Science 316, 870–875 (2007).

  5. 5.

    Coates, A. J. et al. Discovery of heavy negative ions in Titan’s ionosphere. Geophys. Res. Lett. 34, L22103 (2007).

  6. 6.

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

  7. 7.

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

  8. 8.

    Tomasko, M. G. et al. A model of Titan’s aerosols based on measurements made inside the atmosphere. Planet. Space Sci. 56, 669–707 (2008).

  9. 9.

    Dimitrov, V. & Bar-Nun, A. Aging of Titan’s aerosols. Icarus 156, 530–538 (2002).

  10. 10.

    Dimitrov, V. & Bar-Nun, A. Hardening of Titan’s aerosols by their charging. Icarus 166, 440–443 (2003).

  11. 11.

    Cable, M. L. et al. Titan tholins: simulating Titan organic chemistry in the Cassini–Huygens era. Chem. Rev. 112, 1882–1909 (2012).

  12. 12.

    Hörst, S. M. Titan’s atmosphere and climate. J. Geophys. Res. Planets 122, 432–482 (2017).

  13. 13.

    Nahon, L. et al. DESIRS: a state-of-the-art VUV beamline featuring high resolution and variable polarization for spectroscopy and dichroism at SOLEIL. J. Synchrotron Rad. 19, 508–520 (2012).

  14. 14.

    Thuillier, G. et al. Solar irradiance reference spectra for two solar active levels. Adv. Space Res. 34, 256–261 (2004).

  15. 15.

    Gautier, T. et al. Mid- and far-infrared absorption spectroscopy of Titan’s aerosols analogues. Icarus 221, 320–327 (2012).

  16. 16.

    Khare, B. N. et al. Optical constants of organic tholins produced in a simulated Titanian atmosphere: from soft X-ray to microwave frequencies. Icarus 60, 127–137 (1984).

  17. 17.

    Lavvas, P. et al. Energy deposition and primary chemical products in Titan’s upper atmosphere. Icarus 213, 233–251 (2011).

  18. 18.

    López-Puertas, M. et al. Large abundances of polycyclic aromatic hydrocarbons in Titan’s upper atmosphere. Astrophys. J. 770, 132 (2013).

  19. 19.

    Imanaka, H. et al. Laboratory experiments of Titan tholin formed in cold plasma at various pressures: implications for nitrogen-containing polycyclic aromatic compounds in Titan haze. Icarus 168, 344–366 (2004).

  20. 20.

    Quirico, E. et al. New experimental constraints on the composition and structure of tholins. Icarus 198, 218–231 (2008).

  21. 21.

    Mutsukura, N. & Akita, K. Infrared absorption spectroscopy measurements of amorphous CN x films prepared in CH4/N2 r.f. discharge. Thin Solid Films 349, 115–119 (1999).

  22. 22.

    Gavilan, L. et al. X-ray-induced deuterium enrichment of N-rich organics in protoplanetary disks: an experimental investigation using synchrotron light. Astrophys. J. 840, 35 (2017).

  23. 23.

    Skurat, V. Vacuum ultraviolet photochemistry of polymers. Nucl. Instrum. Methods Phys. Res. B 208, 27–34 (2003).

  24. 24.

    Kim, S. J. et al. Retrieval and tentative identification of the 3 μm spectral feature in Titan’s haze. Planet. Space Sci. 59, 699–704 (2011).

  25. 25.

    Mattioda, A. L. et al. Infrared vibrational and electronic transitions in the dibenzopolyacene family. Spectrochim. Acta A Mol. Biomol. Spectrosc. 130, 639–652 (2014).

  26. 26.

    Mattioda, A. L. et al. Infrared spectroscopy of matrix-isolated neutral polycyclic aromatic nitrogen heterocycles: the acridine series. Spectrochim. Acta A Mol. Biomol. Spectrosc. 181, 286–308 (2017).

  27. 27.

    Israel, G. et al. Complex organic matter in Titan’s atmospheric aerosols from in situ pyrolysis and analysis. Nature 438, 796–799 (2005).

  28. 28.

    Carrasco, N., Westlake, J., Pernot, P. & Waite, H. Jr in The Early Evolution of the Atmospheres of Terrestrial Planets 145–154 (Springer, New York, 2013).

  29. 29.

    Vuitton, V. et al. Negative ion chemistry in Titan’s upper atmosphere. Planet. Space Sci. 57, 1558–1572 (2009).

  30. 30.

    Vuitton, V., Yelle, R. V. & McEwan, M. J. Ion chemistry and N-containing molecules in Titan’s upper atmosphere. Icarus 191, 722–742 (2007).

  31. 31.

    Yelle, R. V. et al. Formation of NH3 and CH2NH in Titan’s upper atmosphere. Faraday Discuss. 147, 31–49 (2010).

  32. 32.

    He, C. & Smith, M. A. A comprehensive NMR structural study of Titan aerosol analogs: implications for Titan’s atmospheric chemistry. Icarus 243, 31–38 (2014).

  33. 33.

    Rannou, P. et al. Titan haze distribution and optical properties retrieved from recent observations. Icarus 208, 850–867 (2010).

  34. 34.

    Waite, J. H. Jr et al. Ion neutral mass spectrometer results from the first flyby of Titan. Science 308, 982–986 (2005).

  35. 35.

    Szopa, C., Cernogora, G., Boufendi, L., Correia, J.-J. & Coll, P. PAMPRE: a dusty plasma experiment for Titan’s tholins production and study. Planet. Space Sci. 54, 394–404 (2006).

  36. 36.

    Sciamma-O’Brien, E., Carrasco, N., Szopa, C., Buch, A. & Cernogora, G. Titan’s atmosphere: an optimal gas mixture for aerosol production? Icarus 209, 704–714 (2010).

  37. 37.

    Coll, P. et al. Can laboratory tholins mimic the chemistry producing Titan’s aerosols? A review in light of ACP experimental results. Planet. Space Sci. 77, 91–103 (2013).

  38. 38.

    Cunha de Miranda, B. et al. Molecular isomer identification of Titan’s tholins organic aerosols by photoelectron/photoion coincidence spectroscopy coupled to VUV synchrotron radiation. J. Phys. Chem. A 120, 6529–6540 (2016).

  39. 39.

    Derenne, S. et al. New insights into the structure and chemistry of Titan’s tholins via 13C and 15N solid state nuclear magnetic resonance spectroscopy. Icarus 221, 844–853 (2012).

  40. 40.

    Fleury, B. et al. Influence of CO on Titan atmospheric reactivity. Icarus 238, 221–229 (2014).

  41. 41.

    Carrasco, N., Jomard, F., Vigneron, J., Etcheberry, A. & Cernogora, G. Laboratory analogues simulating Titan’s atmospheric aerosols: compared chemical compositions of grains and thin films. Planet. Space Sci. 128, 52–57 (2016).

  42. 42.

    Mahjoub, A. et al. Influence of methane concentration on the optical indices of Titan’s aerosols analogues. Icarus 221, 670–677 (2012).

  43. 43.

    Mercier, B. et al. Experimental and theoretical study of a differentially pumped absorption gas cell used as a low energy-pass filter in the vacuum ultraviolet photon energy range. J. Vac. Sci. Tech. A 18, 2533–2541 (2000).

Download references


We are grateful to the SOLEIL staff for running the facility and providing beamtime under project number 20120579. We acknowledge J. F. Gil for technical support and the development and design of the sample holder. N.C. and L.G. thank the European Research Council for funding via the ERC PrimChem project (grant agreement 636829). We are grateful to B. Fleury for the preliminary infrared spectroscopic measurements, as well as P. Pernot for helpful discussions. We thank M. Béchard for help and commitment. S.T. acknowledges the University of Paris-Saclay for thesis funding. The work of M.S.G. at the Jet Propulsion Laboratory, California Institute of Technology was performed under a contract with the National Aeronautics and Space Administration and funded through NASA-SSW grant 'Photochemical Processes in Titan’s Atmosphere'. L.N. acknowledges support from the Agence Nationale de la Recherche (ANR-07-BLAN-0293).

Author information


  1. LATMOS/IPSL, UVSQ Université Paris-Saclay, UPMC University, CNRS, Guyancourt, France

    • Nathalie Carrasco
    • , Sarah Tigrine
    •  & Lisseth Gavilan
  2. Institut Universitaire de France, Paris, France

    • Nathalie Carrasco
  3. SOLEIL, l’Orme des Merisiers, Gif-sur-Yvette, France

    • Sarah Tigrine
    •  & Laurent Nahon
  4. Science Division, Jet Propulsion Laboratory, Science Division, California Institute of Technology, Pasadena, CA, USA

    • Murthy S. Gudipati


  1. Search for Nathalie Carrasco in:

  2. Search for Sarah Tigrine in:

  3. Search for Lisseth Gavilan in:

  4. Search for Laurent Nahon in:

  5. Search for Murthy S. Gudipati in:


N.C. supervised the study, helped to perform the irradiation experiments, treated the infrared spectroscopic data and drafted the article. All authors discussed the results and commented on the manuscript. L.G. characterized the sample thickness by ellipsometric measurements. S.T. helped to conduct the irradiation experience. L.N. conceived the irradiation set-up, prepared the beamline for the irradiation conditions and helped to perform the irradiation experiment. M.S.G. was involved in analysis of the data, its interpretation, reaction mechanisms and applications to Titan’s atmosphere.

Competing interests

The authors declare no competing interests.

Corresponding author

Correspondence to Nathalie Carrasco.

About this article

Publication history