[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

*Masahiko Sato¹, Yuhji Yamamoto², Takashi Nishioka², Kazuto KODAMA³, Nobutatsu Mochizuki⁴, Masashi Ushioda⁵, Ryoichi Nakada⁶, Hideo Tsunakawa⁷ (1.The University of Tokyo, 2.Kochi University, 3.Doshisha University, 4.Kumamoto University, 5.National Institute of Advanced Industrial Science and Technology, 6.Japan Agency for Marine-Earth Science and Technology, 7.Japan Aerospace Exploration Agency)

Keywords: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.