2019 Fiscal Year Final Research Report

Creation of the best model of the Earth's core

Research Project

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Project/Area Number	15H05748
Research Category	Grant-in-Aid for Scientific Research (S)
Allocation Type	Single-year Grants
Research Field	Petrology/Mineralogy/Economic geology
Research Institution	Tohoku University
Principal Investigator	Ohtani Eiji 東北大学, 理学研究科, 学術研究員 (60136306)
Co-Investigator(Kenkyū-buntansha)	坂巻竜也東北大学, 理学研究科, 助教 (30630769) 平尾直久公益財団法人高輝度光科学研究センター, 利用研究促進部門, 研究員 (70374915) 福井宏之兵庫県立大学, 物質理学研究科, 助教 (90397901) 宮原正明広島大学, 理学研究科, 准教授 (90400241) 鈴木昭夫東北大学, 理学研究科, 准教授 (20281975)
Project Period (FY)	2015-05-29 – 2020-03-31
Keywords	核 / 軽元素 / 相平衡 / 放射光 / 高温高圧 / 音速 / 状態方程式 / 磁性
Outline of Final Research Achievements	We determined the phase relations, element partitioning, equation of state, sound velocity, and magnetic and crystallographic characteristics of core forming iron alloys by using synchrotron X-ray powder diffraction, inelastic X-ray scattering, and Mossbauer spectroscopy, and neutron powder diffraction. Based on these measurements, we elucidated properties of the iron-light element alloys, and clarified that silicon, oxygen, sulfur, and hydrogen as well as nickel are promising minor elements in the core. Moreover, it was clarified that silicon is the main constituent light element of the inner core. Furthermore, we revealed that the inner core consists of a mixture of hcp phase and B2 phase. We presented a model of the inner core which is composed of a two phase mixture of hcp and B2 phases. This model can explain the enigmatic features of the inner core, the low shear velocity and large Poisson's ratio, which cannot be accounted for by the conventional models of the inner core.
Free Research Field	数物系科学・地球惑星科学
Academic Significance and Societal Importance of the Research Achievements	地球核の研究は地球惑星科学のフロンテイアである．この研究では，超高圧高温実験と放射光X線・中性子線を用いた測定方法の技術開発を行いつつ，地球核を構成する物質の諸物性を解明し，地球核の新たなモデルを構築した．これによって，地球型惑星の構造とその形成過程の理解を増進した．さらに，本研究において開発された実験方法は，関連する物理学・材料科学分野において使用されるなど，地球惑星科学のみならず，広く物性科学，材料科学分野においても貢献をしている．