2015-06-17

第３８４回 †

日時　平成２７年０６月１７日　水曜日　１７時より
場所　東京工業大学　石川台２号館　３１８号室　

＜講師＞　Richard J. Walker 様（メリーランド大学 地質学専攻　教授）
＜題名＞　Late Heavy Bombardment: The Nature of Late-Stage Additions to the Moon and Earth

The Moon and Earth underwent a final minor period of accretion that has commonly been referred to as the Late Heavy Bombardment (LHB) or Terminal Cataclysm. Visual evidence for this “event” in the inner Solar System includes the presence of basins on the Moon, Mercury and Mars that are typically presumed to have formed at about the same time. The LHB is an important process to understand, as it is a potential mechanism for the delivery of water and organic materials to the terrestrial planets, following the high-temperature giant impact stage of planetary growth. Yet, the timing and cause of the LHB, as well as the chemical compositions of the impactors involved remain topics of intense debate.

For the seminar, I will review the history of the LHB concept and provide an overview of reasons cited for and against it being a discrete event in the evolution of our Solar System. Most of the talk will focus on efforts to chemically and isotopically fingerprint the nature of the impactors involved in the basin-forming events, through the analysis of siderophile elements in impact melt rocks from various lunar sites. The application of new, siderophile element isotopic tracers may soon provide a much better understanding of the genetics of the impactors involved.