卡西尼-惠更斯 (Cassini-Huygens) 由軌道太空船卡西尼， 和探測器-惠更斯組成的科學探測儀器。 2004 年7 月1 日 卡西尼到達土星系統後， 便展開了土星系統的科學任務。 探測土星、 土星環、 土星磁球層、 電漿、 影像、 土星的衛星等，泰坦為主要的觀測目標之一。 泰坦除了有濃厚的大氣層外， 在太陽系中和地球最為相似。 氮氣為其主要成分， 甲烷為第二多的氣體。 泰坦上
還存在豐富且複雜的有機物質，如乙烷、 乙炔、 丙烷、 丙炔、 二氧化碳、 氰化物等。 離子與中性物質質譜儀 (INMS) 在卡西尼飛越泰坦大氣時可以測定泰坦大氣中組成成分及氣體密度。 分析26 次飛越任務， 飛越泰坦南半球和北半球上層大氣1000~2000 公里之間， INMS 得到氮氣及甲烷的資料， 發現上層大氣呈現扁圓的狀態， 靠近低緯度地區的氣體密度較高， 大氣結構並不是均勻且
對稱的。 另外溫度的變化可由氣體密度隨高度的變化， 以及標高 (Scale Height) 的計算得到。不同緯度有不同的溫度變化。以氮氣來說， 在1000 公里處， 溫度在不同緯度有很大的變化，北半球133 K ~165 K， 南半球108 K~ 161 K。 在1400 公里處， 北半球151 K ~ 157 K， 南半球152 K ~ 168 K。 上層大氣的加熱機制可能為物質的光分解， 太陽輻射或與土星磁層電漿交互作用而造成的。

Cassini spacecraft is consist of the Cassini orbiter and the Huygens probe. In July 2004, Cassini-Huygens reached Saturn system. In this study, during 26 close encounters with Titan, through northern hemisphere and southern hemisphere, the Ion and Neutral Spectrometer (INMS) instrument on the Cassini spacecraft can be used to measure the atmospheric distributions of different neutral and ion species. Molecular nitrogen is the major species and methane is the second . Preliminary analyses of
the INMS data have shown that the structure of Titan＇s upper atmosphere has significant variations both in latitude and local ( for ions ). It is found that different scale heights are required to fit the density
variations at different altitudinal ranges. Different temperature is calculated. For nitrogen, temperatures close to 1000 km vary strongly with latitude , northern hemisphere, 133~165 K; southern hemisphere, 108~161
K . At 1400 km, northern hemisphere, 151~157 K; southern hemisphere, 152~168 K . Additional heating mechanism might be photolytic effect, solar radiation or Saturn＇s plasma interaction.

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網頁:
NASA JPL http://saturn.jpl.nasa.gov/