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首页> 外文会议>58th International Astronautical Congress 2007 >ORIGIN AND EVOLUTION OF TITAN'S NITROGEN AND METHANE ATMOSPHERE: A POST CASSINI-HUYGENS PERSPECTIVE
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ORIGIN AND EVOLUTION OF TITAN'S NITROGEN AND METHANE ATMOSPHERE: A POST CASSINI-HUYGENS PERSPECTIVE

机译：钛和氮甲烷的起源和演变：后卡西尼·惠更斯的视角

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Titan acquired its nitrogen originally in the form of nitrogen compounds, most likely ammonia, as did the Earth. The extremely low Ar/N_2 found by the Cassini-Huygens GCMS supports this assertion. The conversion of ammonia to nitrogen must have taken place by photolysis by the solar UV early in Titan's accretionary heating phase, again as on primordial Earth. Thermal dissociation of ammonia in Titan's interior could also contribute a small fraction of the total N_2 . Production of N_2 by shock-induced dissociation of NH_3 triggered by an impact [4] is less likely. The present day nitrogen atmosphere of 1.5 bars is the remnant of a much thicker 5-8 bars of N_2 in the past, as indicated by the ~(14)N/~(15)N ratio. Methane, the second most abundant gas on Titan, comprises 5% by volume of the atmosphere. The source and production of methane is most likely in the interior of Titan. The proposed mechanism involves generation of H_2 via serpentinization at low temperature followed by Fischer-Tropsch reaction between H_2 and C, CO_2 or CO and organic material in the crustal pores. Such a process could have taken place during Titan's accretionary heating phase, with methane stored as a stable clathrate-hydrate. The stored methane is subsequently released to the atmosphere either gradually over geologic time, or episodically during impacts, thus replenishing the methane lost to photolysis. Direct capture of methane (as methane clathrate) from Saturn's subnebula , instead of production on the satellite, is less appealing in view of available data on the noble gases and the CO/CH_4 ratio. On Titan, methane has a complex methalogical cycle, complete with surface reservoirs, evaporation, condensation and precipitation, coupled to its loss by photochemistry and escape.
机译：土卫六最初以氮化合物的形式获取其氮，最有可能是氨，而地球也是如此。卡西尼-惠更斯（Cassini-Huygens）GCMS发现的极低的Ar / N_2支持此断言。同样在原始地球上，必须在泰坦的增生加热阶段早期通过太阳紫外线通过光解将氨转化为氮。泰坦内部的氨热分解也可能占总N_2的一小部分。由冲击引发的休克诱导的NH_3分解产生N_2的可能性较小[4]。如〜（14）N /〜（15）N的比值所示，如今的氮气氛为1.5 bar，是过去5-8 bar的N_2厚得多的残余物。甲烷是土卫六上第二丰富的气体，占大气体积的5％。甲烷的来源和生产极有可能在土卫六内部。所提出的机理包括在低温下通过蛇形化生成H_2，然后在H_2与C，CO_2或CO和地壳孔隙中的有机物之间进行费托反应。这种过程可能发生在泰坦的增生阶段，甲烷以稳定的笼形水合物形式存储。随后，所存储的甲烷在地质时间内逐渐释放，或者在撞击过程中逐渐释放到大气中，从而补充了光解损失的甲烷。鉴于现有的稀有气体和CO / CH_4比率数据，直接从土星的子星云捕获甲烷（作为甲烷笼形物）而不是在卫星上生产天然气的吸引力较小。在土卫六上，甲烷具有复杂的气象循环，包括地表储集层，蒸发，冷凝和沉淀，以及由于光化学作用和逸出而损失的甲烷。

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