  In spite of substantial advancements in simulating planet formation, the
planet Mercury's diminutive mass, isolated orbit, and the absence of planets
with shorter orbital periods in the solar system continue to befuddle numerical
accretion models. Recent studies have shown that, if massive embryos (or even
giant planet cores) formed early in the innermost parts of the Sun's gaseous
disk, they would have migrated outward. This migration may have reshaped the
surface density profile of terrestrial planet-forming material and generated
conditions favorable to the formation of Mercury-like planets. Here, we
continue to develop this model with an updated suite of numerical simulations.
We favor a scenario where Earth and Venus' progenitor nuclei form closer to the
Sun and subsequently sculpt the Mercury-forming region by migrating towards
their modern orbits. This rapid formation of ~0.5 Earth-mass cores at ~0.1-0.5
au is consistent with modern high-resolution simulations of planetesimal
accretion. In successful realizations, Earth and Venus accrete mostly dry,
Enstatite Chondrite-like material as they migrate; thus providing a simple
explanation for the masses of all four terrestrial planets, inferred isotopic
differences between Earth and Mars, and Mercury's isolated orbit. Furthermore,
our models predict that Venus' composition should be similar to the Earth's,
and possibly derived from a larger fraction of dry material. Conversely,
Mercury analogs in our simulations attain a range of final compositions.
