Early in the history of the solar system, planetesimals were differentiated into metallic cores. In some planetesimals, this differentiation took place by percolation of the denser core forming liquid through a lighter solid silicate matrix. A key factor in core formation by percolation is the establishment of a connection threshold of the melt. In this work, we report new results from pore network modeling of 3D microtomographic images of 11 synthetic olivine aggregates containing Fe-FeS melt. Our results demonstrate that a melt volume fraction of 0.14 is required to achieve connectivity of the melt. We also show that surface-tension driven melt segregation during annealing experiments plays an important role in controlling this threshold melt fraction. We also report that, contrary to the generally accepted notion, melt pinch-off is caused by reduction in pore size, rather than melt drainage out of throats. Using the results of our study, we estimate that the peak melt segregation velocity in a planetesimal of 100 km radius can be as high as 41 m/yr and core segregation can be completed in less than 0.5 million years.

在太阳系历史的早期，小行星被区分为金属核。在某些小行星中，这种区分是通过较轻的固体硅酸盐基质渗透形成的致密核液体而发生的。通过渗流形成芯的关键因素是熔体的连接阈值的确定。在这项工作中，我们报告了11种含有Fe-FeS熔体的合成橄榄石聚集体的3D显微断层图像的孔网络建模的新结果。我们的结果表明，要实现熔体的连通性，需要熔体体积分数为0.14。我们还表明，在退火实验过程中，表面张力驱动的熔体偏析在控制此阈值熔体分数中起着重要作用。我们还报告说，与普遍接受的概念相反，熔体夹断是由孔径减小引起的，而不是由喉咙中的熔体排出引起的。利用我们的研究结果，我们估计在100 km半径的小行星上的峰值熔体离析速度可以高达41 m / yr，并且岩心离析可以在不到50万年的时间内完成。