报告题目：The lunar regolith: what can it reveal about the history of the Moon? 

　　报告人：Greg Michael （Freie Universit？t Berlin Germany）  

　　摘要：The lunar regolith is a fragmental mixture generated by a long sequence of impacts at all scales. The Apollo and Luna samples of brecciated rocks contain impact melt clasts which can be dated by radioisotope methods back to the earliest times of the surface history. It is clear from the number of ancient clasts that such material is a ubiquitous fraction of the surface regolith. It follows that if traces of ancient impact events have survived with measurable abundance, all the intervening events should also have left their mark. By modelling the impact history of the Moon, we estimate the present-day abundance of material at the surface which would carry a measurable radioisotope age resulting from specific impact events. 

　　 A new development in dating planetary surfaces from their impact crater populations allows meaningful age estimates based on fewer superposed craters than previously.  The method makes it possible to date smaller features, and it is applied here to constrain the ages of several-km impact craters in the vicinity of the planned Chang’E-5 landing site. A small component of ejecta from some of these craters could be present in the returned regolith core, and knowledge of their timing could help to identify the source.  

　　时间：4月17日（周三）下午2点  

　　地点：紫台仙林园区 2-208 会议室  

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紫金山天文台学术委员会