Huygens Articles

Nature 438, 765-778 (8 December 2005) | doi:10.1038/nature04126; Received 26 May 2005; Accepted 8 August 2005; Published online 30 November 2005

Rain, winds and haze during the Huygens probe's descent to Titan's surface

M. G. Tomasko1, B. Archinal2, T. Becker2, B. Bézard3, M. Bushroe1, M. Combes3, D. Cook2, A. Coustenis3, C. de Bergh3, L. E. Dafoe1, L. Doose1, S. Douté4, A. Eibl1, S. Engel1, F. Gliem5, B. Grieger6, K. Holso1, E. Howington-Kraus2, E. Karkoschka1, H. U. Keller6, R. Kirk2, R. Kramm6, M. Küppers6, P. Lanagan1, E. Lellouch3, M. Lemmon7, J. Lunine1,8, E. McFarlane1, J. Moores1, G. M. Prout1, B. Rizk1, M. Rosiek2, P. Rueffer5, S. E. Schröder6, B. Schmitt4, C. See1, P. Smith1, L. Soderblom2, N. Thomas9 & R. West10

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The irreversible conversion of methane into higher hydrocarbons in Titan's stratosphere implies a surface or subsurface methane reservoir. Recent measurements from the cameras aboard the Cassini orbiter fail to see a global reservoir, but the methane and smog in Titan's atmosphere impedes the search for hydrocarbons on the surface. Here we report spectra and high-resolution images obtained by the Huygens Probe Descent Imager/Spectral Radiometer instrument in Titan's atmosphere. Although these images do not show liquid hydrocarbon pools on the surface, they do reveal the traces of once flowing liquid. Surprisingly like Earth, the brighter highland regions show complex systems draining into flat, dark lowlands. Images taken after landing are of a dry riverbed. The infrared reflectance spectrum measured for the surface is unlike any other in the Solar System; there is a red slope in the optical range that is consistent with an organic material such as tholins, and absorption from water ice is seen. However, a blue slope in the near-infrared suggests another, unknown constituent. The number density of haze particles increases by a factor of just a few from an altitude of 150 km to the surface, with no clear space below the tropopause. The methane relative humidity near the surface is 50 per cent.

  1. Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd, Tucson, Arizona 85721-0092, USA
  2. US Geological Survey, Astrogeology, 2225 N. Gemini Drive, Flagstaff, Arizona 86001, USA
  3. LESIA, Observatoire de Paris, 5 place Janssen, 92195 Meudon, France
  4. Laboratoire de Planétologie de Grenoble, CNRS-UJF, BP 53, 38041 Grenoble, France
  5. Technical University of Braunschweig, Hans-Sommer-Str. 66, D-38106 Braunschweig, Germany
  6. Max Planck Institute for Solar System Research, Max-Planck-Str. 2, D-37191 Katlenburg-Lindau, Germany
  7. Department of Physics, Texas A&M University, College Station, Texas 77843-3150, USA
  8. Istituto Nazionale di Astrofisica — Istituto di Fisica dello Spazio Interplanetario (INAF-IFSI ARTOV), Via del Cavaliere, 100, 00133 Roma, Italia
  9. Department of Physics, University of Bern, Sidlerstr. 5, CH-3012 Bern, Switzerland
  10. Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, California 91109, USA

Correspondence to: C. See1 Correspondence and requests for materials should be addressed to C.S. (Email: csee@lpl.arizona.edu).

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