Article | Published:

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

Nature Astronomyvolume 2pages489494 (2018) | Download Citation

Abstract

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.

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Acknowledgements

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

Affiliations

  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

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Contributions

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.

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DOI

https://doi.org/10.1038/s41550-018-0439-7