Prof. William F. McDonough and an ex-GP-EES Student Takashi Yoshizaki have pinpointed the strong magnetic field of the early sun as the reason behind the radial variation of rock and metal in rocky planets’ cores. This magnetic field, which pulled small iron grains inward, explains Mercury’s big iron core and why Mars has so little iron in its core.
 
This research was published in the Journal Progress in Earth and Planetary Science on July 5.
 
 
 
Title: Terrestrial planet compositions controlled by accretion disk magnetic field
Author: William F. McDonough and Takashi Yoshizaki
 

See below websites for more details.
https://doi.org/10.1186/s40645-021-00429-4
https://www.tohoku.ac.jp/en/press/why_does_mercury_have_big_iron_core.html