Abstract

Saturn's largest moon, Titan, remains an enigma, explored only by remote sensing from Earth, and by the Voyager and Cassini spacecraft. The most puzzling aspects include the origin of the molecular nitrogen and methane in its atmosphere, and the mechanism(s) by which methane is maintained in the face of rapid destruction by photolysis. The Huygens probe, launched from the Cassini spacecraft, has made the first direct observations of the satellite's surface and lower atmosphere. Here we report direct atmospheric measurements from the Gas Chromatograph Mass Spectrometer (GCMS), including altitude profiles of the constituents, isotopic ratios and trace species (including organic compounds). The primary constituents were confirmed to be nitrogen and methane. Noble gases other than argon were not detected. The argon includes primordial ³⁶Ar, and the radiogenic isotope ⁴⁰Ar, providing an important constraint on the outgassing history of Titan. Trace organic species, including cyanogen and ethane, were found in surface measurements.

1. National Aeronautics and Space Administration, Greenbelt, Maryland 20771, USA
2. University of Michigan, Ann Arbor, Michigan 48109-2143, USA
3. Institute for Meteorology and Geophysics, University of Graz, A-8010 Graz, Austria
4. LESIA, Observatoire de Paris-Meudon, F-92195 Meudon Cedex, France
5. Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85716, USA
6. Service d'Aéronomie du CNRS, F-91371 Verrières le Buisson Cedex, France
7. University of Alabama, CMC, 817 22nd Street South, Birmingham, Alabama 35205, USA
8. University of Hawaii, Honolulu, Hawaii 96822, USA
9. Laboratoire Interuniversitaire des Systèmes Atmosphériques, Université Paris 12 et Paris 7, Avenue du Général de Gaulle, F-94010 Creteil Cedex, France

Correspondence to: H. B. Niemann¹ Correspondence and requests for materials should be addressed to H.B.N. (Email: Hasso.B.Niemann@nasa.gov).

Received 2 June 2005; Accepted 3 August 2005

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