  The formation of the four terrestrial planets of the solar system is one of
the most fundamental problems in the planetary sciences. However, the formation
of Mercury remains poorly understood. We investigated terrestrial planet
formation by performing 110 high-resolution N-body simulation runs using more
than 100 embryos and 6000 disk planetesimals representing a primordial
protoplanetary disk. To investigate the formation of Mercury, these simulations
considered an inner region of the disk at 0.2-0.5 au (the Mercury region) and
disks with and without mass enhancements beyond the ice line location, aIL, in
the disk, where aIL = 1.5, 2.25, and 3.0 au were tested. Although Venus and
Earth analogs (considering both orbits and masses) successfully formed in the
majority of the runs, Mercury analogs were obtained in only nine runs. Mars
analogs were also similarly scarce. Our Mercury analogs concentrated at orbits
with a ~ 0.27-0.34 au, relatively small eccentricities/inclinations, and median
mass m ~ 0.2 Earth masses. In addition, we found that our Mercury analogs
acquired most of their final masses from embryos/planetesimals initially
located between 0.2 and ~1-1.5 au within 10 Myr, while the remaining mass came
from a wider region up to ~3 au at later times. Although the ice line was
negligible in the formation of planets located in the Mercury region, it
enriched all terrestrial planets with water. Indeed, Mercury analogs showed a
wide range of water mass fractions at the end of terrestrial planet formation.
