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The basic structure of the solar system is set by the presence of low-massterrestrial planets in its inner part and giant planets in its outer part. Thisis the result of the formation of a system of multiple embryos withapproximately the mass of Mars in the inner disk and of a few multi-Earth-masscores in the outer disk, within the lifetime of the gaseous component of theprotoplanetary disk. What was the origin of this dichotomy in the massdistribution of embryos/cores? We show in this paper that the classic processesof runaway and oligarchic growth from a disk of planetesimals cannot explainthis dichotomy, even if the original surface density of solids increased at thesnowline. Instead, the accretion of drifting pebbles by embryos and cores canexplain the dichotomy, provided that some assumptions hold true. We proposethat the mass-flow of pebbles is two-times lower and the characteristic size ofthe pebbles is approximately ten times smaller within the snowline than beyondthe snowline (respectively at heliocentric distance $r<r_{ice}$ and$r>r_{ice}$, where $r_{ice}$ is the snowline heliocentric distance), due to icesublimation and the splitting of icy pebbles into a collection ofchondrule-size silicate grains. In this case, objects of original sub-lunarmass would grow at drastically different rates in the two regions of the disk.Within the snowline these bodies would reach approximately the mass of Marswhile beyond the snowline they would grow to $\sim 20$ Earth masses. Theresults may change quantitatively with changes to the assumed parameters, butthe establishment of a clear dichotomy in the mass distribution of protoplanetsappears robust, provided that there is enough turbulence in the disk to preventthe sedimentation of the silicate grains into a very thin layer.

The great dichotomy of the Solar System: small terrestrial embryos and massive giant planet cores