West R A, Brown M E, Salinas S V, Bouchez A H, Roe H G
MS 169-237 Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, California 91109, USA.
Nature. 2005 Aug 4;436(7051):670-2. doi: 10.1038/nature03824.
With its substantial atmosphere of nitrogen, hydrocarbons and nitriles, Saturn's moon Titan is a unique planetary satellite. Photochemical processing of the gaseous constituents produces an extended haze that obscures the surface. Soon after the Voyager fly-bys in 1980 and 1981 photochemical models led to the conclusion that there should be enough liquid methane/ethane/nitrogen to cover the surface to a depth of several hundred metres. Recent Earth-based radar echoes imply that surface liquid may be present at a significant fraction of the locations sampled. Here we present ground-based observations (at near-infrared wavelengths) and calculations showing that there is no evidence thus far for surface liquid. Combined with the specular signatures from radar observations, we infer mechanisms that produce very flat solid surfaces, involving a substance that was liquid in the past but is not in liquid form at the locations we studied.
土星的卫星土卫六拥有浓厚的氮气、碳氢化合物和腈类大气层，是一颗独特的行星卫星。气态成分的光化学过程产生了一层延伸的薄雾，遮蔽了表面。1980年和1981年旅行者号飞掠之后不久，光化学模型得出结论，应该有足够的液态甲烷/乙烷/氮气覆盖表面达数百米深。最近基于地球的雷达回波表明，在采样的大部分地点可能存在地表液体。在此，我们展示了地面观测（近红外波长）和计算结果，表明目前尚无地表液体的证据。结合雷达观测的镜面特征，我们推断出产生非常平坦固体表面的机制，涉及一种过去是液态但在我们研究的地点并非液态的物质。
