[S-EM19] Earth and planetary magnetism: Observations, modeling, and implications on dynamics and evolution

[SEM19-02] Constraints on the Source of the Martian Magnetic Anomalies Inferred From Relaxation Time of Remanent Magnetization

★Invited Papers

*佐藤 雅彦¹、山本 裕二²、西岡 孝²、小玉 一人³、望月 伸竜⁴、潮田 雅司⁵、中田 亮一⁶、綱川 秀夫⁷ (1.東京大学、2.高知大学、3.同志社大学、4.熊本大学、5.産業技術総合研究所、6.海洋研究開発機構、7.宇宙航空研究開発機構)

キーワード：Martian magnetic anomaly、magnetite、relaxation time of remanent magnetization

The strong magnetic anomalies observed over Mars originate from remanence of deep crust, which should be preserved during 4 billion years. We estimate the relaxation time of remanence carried by various types of magnetite, considering temperature and pressure dependences of magnetic parameters. The estimation shows that acicular-shaped single-domain magnetite is needed to retain the thick magnetized layer during 4 billion years in a low-Urey ratio scenario, whereas acicular-shaped single-domain, equidimensional single-domain, and pseudo-single-domain magnetites can be the source of anomalies in a high-Urey ratio scenario. In each case, fine-grained (<10 μm) and preferably high-aspect-ratio magnetite in deep crust is needed to explain the observed anomalies.