The present atmosphere of Titan exhibits evidence of extensive evolution, in the form of rapid photochemical destruction of methane and a large fractionation of the nitrogen and oxygen isotopes. Attempts to recover the initial inventory of volatiles lead toward a model in which nitrogen was originally supplied as NH3, essentially unmodified from its relative abundance in the outer solar nebula. Titan's atmospheric methane, in contrast, appears to have been formed from carbon and other carbon compounds, either by gas phase reactions in the subnebula or by accretional heating during the formation of Titan. These conclusions can be tested by further studies of abundances and isotope ratios in Titan's atmosphere, augmented by studies of comets. The possible similarity of carbon and nitrogen inventories on Titan to those on the inner planets makes this investigation particularly intriguing.

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论泰坦大气的起源

泰坦目前的大气层显示出广泛演化的证据，形式是甲烷的快速光化学破坏和氮和氧同位素的大量分馏。试图恢复挥发物的初始库存导致了一个模型，其中氮最初以 NH3 形式提供，基本上没有改变其在外太阳星云中的相对丰度。相比之下，泰坦的大气甲烷似乎是由碳和其他碳化合物形成的，要么是通过亚星云中的气相反应，要么是泰坦形成过程中的吸积加热。这些结论可以通过进一步研究泰坦大气中的丰度和同位素比率来验证，并通过对彗星的研究得到加强。