[S-IT21] Planetary cores: Structure, formation, and evolution

[SIT21-P05] Experimental study on the timescale of core segregation in planetasimals

*Hidenori Terasaki¹, Takumi Miura², Tadashi Kondo², Takashi Yoshino³ (1.Faculty of Science, Okayama University, 2.Department of Earth and Space science, Osaka University, 3.Institute for Planetary Materials, Okayama University)

Keywords:planetesimal, timescale

Many planetesimals and protoplanets are believed to have been differentiated to the core and mantle prior to build the terrestrial planets. Early core formation in such small bodies has been reported based on Hf-W system (e.g., Kleine et al. 2002). Although segregation velocity of Fe-S melt in olivine matrices was estimated based on experiments (Roberts et al. 2007), the timescale of core formation in small bodies was not enough to be constrained. Here, we experimental investigated the timescale of core melt segregation in the solid opx mantle at interior conditions of small bodies.

High pressure and temperature experiments were carried out using the piston cylinder and multi-anvil apparatus. Fe–S layer was sandwiched synthetic opx (Fe#=0.23-0.30) layers. The sample was enclosed into graphite capsule. The experiments were performed up to 2.5 GPa and 1523 K for 15 min to 1 hour. Textural observation and chemical analysis of the recovered samples were carried out using SEM-EDS and electron microprobe.

Textures in the recovered samples showed that Fe-S melt percolated through the opx grain boundaries at 0.5 GPa while the no segregation of the melt was found at 2.5 GPa. Based on the obtained segregation velocity of the Fe-S melt, we estimated timescale of core melt segregation in planetesimals and protoplanets and compared the results with the core formation timescale of asteroid reported from Hf-W chronometry (~ 4 Myr).