Lunine J I
Lunar and Planetary Laboratory, University of Arizona, Tucson 85721, USA.
Orig Life Evol Biosph. 1997 Jun;27(1-3):205-24.
The solar system is thought to have begun in a flattened disk of gas and dust referred to traditionally as the solar nebula. Such a construct seems to be a natural product of the collapse of dense parts of giant molecular clouds, the vast star-forming regions that pepper the Milky Way and other galaxies. Gravitational, magnetic and thermal forces within the solar nebula forced a gradual evolution of mass toward the center (where the sun formed) and angular momentum (borne by a small fraction of the mass) toward the outer more distant regions of the disk. This evolution was accompanied by heating and a strong temperature contrast from the hot, inner regions to the cold, more remote parts of the disk. The resulting chemistry in the disk determined the initial distribution of organic matter in the planets; most of the reduced carbon species, in condensed form, were located beyond the asteroid belt (the 'outer' solar system). The Earth could have received much of its inventory of pre-biological material from comets and other icy fragments of the process of planetary formation in the outer solar system.
太阳系被认为起源于一个传统上被称为太阳星云的由气体和尘埃组成的扁平圆盘。这样一种结构似乎是巨大分子云致密部分坍缩的自然产物，巨大分子云是点缀在银河系和其他星系中的广阔恒星形成区域。太阳星云中的引力、磁力和热力促使质量逐渐向中心（太阳形成的地方）聚集，而角动量（由一小部分质量携带）则向圆盘更遥远的外部区域转移。这种演化伴随着加热以及从圆盘炎热的内部区域到寒冷的更偏远部分的强烈温度反差。圆盘中产生的化学过程决定了行星中有机物的初始分布；大多数以凝聚形式存在的还原碳物种位于小行星带之外（“外”太阳系）。地球可能从外太阳系行星形成过程中的彗星和其他冰质碎片那里获得了大量的前生物物质。
