title: Rain, winds and haze during the Huygens probe's descent to Titan's surface.
abstract: 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.
authors.affiliation: Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd, Tucson, Arizona 85721-0092, USA.
authors.forename: M G
authors.initials: MG
authors.lastname: Tomasko
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authors.lastname: Archinal
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authors.lastname: Becker
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authors.initials: B
authors.lastname: Bézard
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authors.lastname: Bushroe
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authors.lastname: Combes
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authors.lastname: Cook
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authors.lastname: Coustenis
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authors.lastname: de Bergh
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authors.lastname: Eibl
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authors.lastname: Gliem
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authors.lastname: Grieger
authors.forename: K
authors.initials: K
authors.lastname: Holso
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authors.lastname: Howington-Kraus
authors.forename: E
authors.initials: E
authors.lastname: Karkoschka
authors.forename: H U
authors.initials: HU
authors.lastname: Keller
authors.forename: R
authors.initials: R
authors.lastname: Kirk
authors.forename: R
authors.initials: R
authors.lastname: Kramm
authors.forename: M
authors.initials: M
authors.lastname: Küppers
authors.forename: P
authors.initials: P
authors.lastname: Lanagan
authors.forename: E
authors.initials: E
authors.lastname: Lellouch
authors.forename: M
authors.initials: M
authors.lastname: Lemmon
authors.forename: J
authors.initials: J
authors.lastname: Lunine
authors.forename: E
authors.initials: E
authors.lastname: McFarlane
authors.forename: J
authors.initials: J
authors.lastname: Moores
authors.forename: G M
authors.initials: GM
authors.lastname: Prout
authors.forename: B
authors.initials: B
authors.lastname: Rizk
authors.forename: M
authors.initials: M
authors.lastname: Rosiek
authors.forename: P
authors.initials: P
authors.lastname: Rueffer
authors.forename: S E
authors.initials: SE
authors.lastname: Schröder
authors.forename: B
authors.initials: B
authors.lastname: Schmitt
authors.forename: C
authors.initials: C
authors.lastname: See
authors.forename: P
authors.initials: P
authors.lastname: Smith
authors.forename: L
authors.initials: L
authors.lastname: Soderblom
authors.forename: N
authors.initials: N
authors.lastname: Thomas
authors.forename: R
authors.initials: R
authors.lastname: West
mesh_terms: D001272:Atmosphere / Q000737:chemistry*; D005118:Extraterrestrial Environment / Q000737:chemistry*; D006813:Humidity; D007053:Ice / Q000032:analysis; D008697:Methane / Q000032:analysis / Q000737:chemistry; D011891:Rain; D013026:Space Flight; D014919:Wind
chemical_list: D007053:Ice; D008697:Methane