Lunine J I, McKay C P
Lunar and Planetary Laboratory, University of Arizona, Tucson 85721, USA.
Adv Space Res. 1995 Mar;15(3):303-11. doi: 10.1016/s0273-1177(99)80101-x.
The surface and atmosphere of Titan constitute a system which is potentially as complex as that of the Earth, with the possibility of precipitation, surface erosion due to liquids, chemistry in large surface or subsurface hydrocarbon reservoirs, surface expressions of internal activity, and occasional major impacts leading to crustal melting. While none of the above have been observed as yet, the composition, density and thermal properties of Titan's atmosphere make it uniquely suited in the outer solar system as a place where such processes may occur. The one attribute of the Earth not expected on Titan is biological activity, which has had a profound effect on the evolution of the Earth's surface-atmosphere system. The earliest environment of Titan could have been warm enough for liquid ammonia-water solutions to exist on or near surface; pre-biotic organic processes may have taken place in such an environment. After a few hundred million years surface ammonia-water would have disappeared. Therefore, study of Titan through the Cassini-Huygens mission, planned for launch in 1997, primarily affords the opportunity to understand planet-wide surface-atmosphere interactions in the presence of fluids but in the absence of life. More speculative is the possibility that endogenic and exogenic heating continue to provide short-lived environments on Titan wherein pre-biotic organic processes in the presence of water happen.
土卫六的表面和大气构成了一个系统，其潜在的复杂性可能与地球的系统相当，存在降水的可能性、液体导致的表面侵蚀、大型地表或地下碳氢化合物储层中的化学过程、内部活动的地表表现，以及偶尔导致地壳熔化的重大撞击。虽然上述情况目前尚未被观测到，但土卫六大气的成分、密度和热性质使其在外太阳系中成为此类过程可能发生的独特场所。地球的一个在土卫六上不太可能出现的特征是生物活动，生物活动对地球表面 - 大气系统的演化产生了深远影响。土卫六最早的环境可能足够温暖，使得液态氨 - 水溶液能够存在于表面或其附近；在前生物环境中，有机过程可能在这样的环境中发生。经过几亿年，表面的氨 - 水将会消失。因此，计划于1997年发射的卡西尼 - 惠更斯任务对土卫六的研究，主要提供了一个机会，来了解在有流体但无生命存在的情况下，全球范围内的表面 - 大气相互作用。更具推测性的是，内源性和外源性加热是否会继续在土卫六上提供短暂的环境，使水存在时的前生物有机过程得以发生。
