Investigating chronological evidence of a giant impact in the early history of asteroid Vesta

2023 Fiscal Year Final Research Report

• Project/Area Number: 19K03946
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17010:Space and planetary sciences-related
• Research Institution: Tokyo Institute of Technology
• Principal Investigator: Haba Makiko 東京工業大学, 理学院, 助教 (30598438)
• Project Period (FY): 2019-04-01 – 2024-03-31
• Keywords: Vesta / zircon / U-Pb / Pu-Xe / HED / meteorite

Outline of Final Research Achievements

To explore the possibility of giant impacts during the early formation of asteroid Vesta, age measurements of HED meteorites, which originate from Vesta, were conducted for geochronological verification. Firstly, high-precision U-Pb dating was performed using zircons in basaltic eucrites to verify if the age of the impacts could be determined. The age of zircons in the Camel Donga meteorite, used in this study, successfully reduced the error margin associated with traditional methods to less than one-tenth. However, all the zircon grains analyzed indicated the age of crust formation. Additionally, the 244Pu-Xe dating of whole rock howardite samples yielded ages corresponding to the early evolution of Vesta, but did not detect the age of a giant impact.

Free Research Field

Geochemistry

Academic Significance and Societal Importance of the Research Achievements

小惑星ベスタにおける巨大衝突の可能性を探るため，ジルコンの高精度U-Pb年代測定法の改良に取り組んだ．HED隕石中のジルコンはベスタの地殻の初期進化を考える上で重要な年代情報を与えるが，ジルコンの粒径が小さいため，二次イオン質量分析計を用いた年代測定が行われている．この手法では年代に対して2000万年以上の誤差がつくため，初期イベントを年代学的に分離するために高精度な年代が必要とされている．本研究では年代誤差を100万年以下に低減することに成功しており，本手法が複数のHED隕石に適応されることで，ベスタの地殻の形成史が明らかになり，原始惑星の進化プロセスへの理解が深まることが期待される．