[S-CG48] 観測・実験・シミュレーションから見えてきた惑星内部

[SCG48-P03] Paleointensity estimation of ancient Mars using the magnetic anomaly data

*佐藤 雅彦¹、潮田 雅司²、中田 亮一³、田村 裕二郎⁴、山本 伸次⁴、小澤 一仁⁵、高橋 太⁶、坂田 遼弥⁷、関 華奈子⁵ (1.東京理科大学、2.四国総合研究所、3.海洋研究開発機構、4.横浜国立大学、5.東京大学、6.九州大学、7.東北大学)

キーワード：Mars、Paleointensity、Magnetic anomaly、Exsolved magnetite

Magnetic field observations of Mars revealed that there are strong magnetic anomalies arising from the crustal remanences, which is estimated to be about 10 times as strong as the Earth’s crustal magnetization. The strong crustal remanences require a particular origin such as the strong dynamo field of the ancient Mars, the high concentration of ferromagnetic mineral in the Martian crust, and so on. Plagioclase, one of the common constituents of terrestrial crustal rocks, sometimes contain fine-grained magnetite crystals exsolved from Fe-bearing magmatic plagioclase at subsolidus condition. The natural remanent magnetization carried by the exsolved magnetite in plagioclase is likely candidate of the source of Martian magnetic anomaly in terms of the remanence stability. In this study, a suite of experiments (magnetic measurements, synchrotron radiation study, and microscopic observation) and calculations (thermodynamic calculation with the rhyolite-MELTS program) were carried out to estimate the concentrations of exsolved magnetite in the Martian crust and the paleo-planetary field intensity of Mars based on the crustal remanence records. The results indicate that the Martian crustal rocks are high in concentrations of exsolved magnetite, which efficiently acquires the thermoremanent magnetization, resulting in the high remanence acquisition efficiency of the Martian crust. The paleo-planetary field intensity of Mars is estimated to be 10–20 μT using the crustal remanence and acquisition efficiency values. On the basis of the magnetic field intensity, we will discuss the histories of Martian magnetic field and water escape from Martian surface.