The Martian magnetic field intensity estimation based on the magnetic properties of exsolved magnetite

2020 Fiscal Year Final Research Report

• Project/Area Number: 19K14777
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 17010:Space and planetary sciences-related
• Research Institution: The University of Tokyo
• Principal Investigator: Sato Masahiko 東京大学, 大学院理学系研究科(理学部), 助教 (50723277)
• Project Period (FY): 2019-04-01 – 2021-03-31
• Keywords: 斜長石 / 磁鉄鉱 / 離溶 / 火星 / 惑星磁場

Outline of Final Research Achievements

This study prepared the plagioclase crystal samples from natural mafic-plutonic rocks, and the magnetic hysteresis loop measurement using an Alternating Gradient Magnetometer, the microscopic observation using electron microprobes, and the X-ray absorption near edge structure measurement at synchrotron radiation facilities were conducted for the single grain plagioclase crystals. It was confirmed that there was inverse relationship between the magnetite content and average valence states of Fe. In addition, the intensity of thermoremanent magnetization was mesuremed for plagiolcase crystals. The content of the exsolved magnetite in the Martian crustal rock and the intensity of crustal magnetization were calculated on the basis of the empirically obtained relationships and the thermodynamic calculations. Comparing the calculated and observed crustal magnetizations, the magnetic field intensity of Mars was estimated.

Free Research Field

岩石磁気学

Academic Significance and Societal Importance of the Research Achievements

過去の惑星磁場強度に関する情報は，惑星内部ダイナミクス状態を知る重要な指標であり，表層環境の進化を知る上でも必要不可欠である．しかし形成初期における火星の磁場強度に関する情報は，そのデータ量・質ともに不十分であり解明が急務となっていた．本研究では，斜長石中に含まれる離溶磁鉄鉱の磁気的性質を用いた新手法により問題解決を試みた．実験・計算から火星地殻中に含まれる離溶磁鉄鉱の含有量および離溶磁鉄鉱の残留磁化強度を求め，得られた実験データを用いて人工衛星によって観測された離溶磁鉄鉱の磁場記録を読み解く事で，形成初期における火星の磁場強度の推定値を得ることに成功した．