Transformation of Solar dust to Earth dust

2022 Fiscal Year Final Research Report

• Project/Area Number: 19H00712
• Research Category: Grant-in-Aid for Scientific Research (A)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Medium-sized Section 17:Earth and planetary science and related fields
• Research Institution: The University of Tokyo
• Principal Investigator: Tachibana Shogo 東京大学, 大学院理学系研究科(理学部), 教授 (50361564)
• Co-Investigator(Kenkyū-buntansha): 瀧川 晶 東京大学, 大学院理学系研究科(理学部), 准教授 (10750367) ; 川崎 教行 北海道大学, 理学研究院, 准教授 (50770278) ; 圦本 尚義 北海道大学, 理学研究院, 教授 (80191485)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Keywords: 原始惑星系円盤 / 非晶質ケイ酸塩 / ダスト / 酸素同位体 / 反応速度論

Outline of Final Research Achievements

The oxygen isotope exchange rate between amorphous silicate dust and disk gas was determined by low-pressure experiments along with the temperature dependence of the exchange rate and the reaction mechanism. The oxygen isotope exchange between amorphous silicate dust and disk gas was found to be controlled by diffusion in the amorphous silicate. A theoretical equation predicting the temperature at which chemical reactions effectively occur in dust moving in a protoplanetary disk with steady accretion was constructed, and the oxygen isotope exchange temperature of submicron-sized amorphous silicate dust was determined. Oxygen isotope exchange is completed at 650-800 K and 750-900 K for amorphous forsterite and amorphous enstatite dust, respectively, indicating that the evolution of oxygen isotope composition from solar-type dust to Earth-type dust occurred in the early Solar System.

Free Research Field

宇宙化学

Academic Significance and Societal Importance of the Research Achievements

地球や月，火星，小惑星の構成物質の酸素同位体組成は，太陽とは異なり，太陽と同じ酸素同位体組成をもつ太陽系初期ダストが，原始惑星系円盤ガスと酸素同位体交換を起こし，地球型の酸素同位体に変化したと考えられている，本研究では，実験で非晶質ケイ酸塩ダストと円盤ガスとの酸素同位体交換速度を求めた．また，原始惑星系円盤でダストの化学反応が効率的に起こる温度を決定する理論式を構築し，フォルステライト・エンスタタイト・かんらん石組成の非晶質ケイ酸塩ダストについて，それぞれ 650-800，750-900，500-600 K で酸素同位体交換が完了し，太陽型ダストが地球型ダストへと進化しうることがわかった．