碰撞作用与类地行星起源探讨

类地行星挥发性元素普遍亏损很可能是由于太阳星云早期剧烈的太阳活动引起的。当气体、尘粒、挥发性元素和水被驱赶出内太阳系时，只有米级到公里级的物质保存下来并堆积成星子，最终吸积星子形成类地行星。我们认为类地行星的初始物质主要是已分异的星子和一些未分异的球粒陨石质星子或不同类型的陨石母体，最靠近太阳形成的星子具有最低的ＦｅＯ／（ＦｅＯ＋ＭｇＯ）值，水星是在靠近太阳的高度还原条件下吸积成分类似ＥＨ球粒陨石的星子形成的。地球的初始物质为分异的铁陨石及Ｈ群球粒陨石。随着距太阳距离增大及温度降低，陨石形成的部位大致为：ＥＨ、ＥＬ－ＩＡＢ－ＳＮＣ（辉玻无球粒陨石、辉橄无球粒陨石、纯橄无球粒陨石）－Ｅｕｃ（钙长辉长无球粒陨石）－Ｈ、Ｌ、ＬＬ－ＣＶ、ＣＭ、ＣＯ－Ｃｌ－彗星。物体之间、星子之间及行星与星子之间的碰撞对太阳系的形成和演化起着重要的作用。

IMPACT PROCESS AND ITS ROLE IN ORIGIN OF TERRESTRIAL PLANETS

The common depletion of volatile elements in terrestrial planets was probably caused by the early violent activities of the inner solar nebula. The growth of planetesimals took place during gases, dusts, volatile elements and water were driven out of the inner solar system. But only those bodies that range from meters to kilometers in diameter would survive, and eventually accumulate into planetesimals that ultimately formed the terrestrial planets. It is suggested that the primitive materials responsible for the terrestrial planets were mostly the well differentiated planetesimals and some undifferentiated chondritic planetesimals or different types of meteorite parent bodies. The planetesimals forming near the sun are expected to have a low FeO/(FeO + MgO) ratio. The Mercury forming under highly reducing condition near the sun was accreted from planetesimals similar to the EH chondrites in chemical composition. The primitive material of the Earth were the differentiated iron meteorites and H chondrites. With increasing distance and decreasing temperature from the sun, the formation location sequence of meteorites are approximately in such an order:EH,EL-IAB-SNC-Euc-H,L,LL-CV,CM,CO-CI-Comets.The collision between various bodies, planetesimals, planets and large planetesimals must have played a significant role in the origin and evolution of the solar system.