[P-PS22] 太陽系における惑星物質の形成と進化

[PPS22-25] 小惑星ベスタにおけるダイオジェナイト形成の為の結晶化・冷却条件

*川畑 佑典¹、永原 裕子¹ (1.東京大学大学院理学系研究科地球惑星科学専攻)

キーワード：マグマオーシャン, 小惑星ベスタ, HED隕石

The asteroid 4 Vesta has been completely differentiated to core and mantle despite its small size, of which surface materials are howardite-eucrite-diogenite (HED) meteorites that we know the detailed petrology, and therefor, is a good target for understanding differentiation of terrestrial planets. A new differentiation model for crust formation was developed by taking magma ocean fluid dynamics, chemical equilibrium, presence of ²⁶Al, and cooling into consideration with special care to crystal separation. The role of crystal size, thickness of the conductive lib, and fO₂ are evaluated as parameters. Large crystals (1cm) settle and form a km-thick cumulate layer of orthopyroxene with Mg# of 0.70-0.90 in 20 thousand years, which almost agrees with the Mg# of diogenites, whereas thinner layers are formed if the grain size is smaller.