  Radiometric dating indicates that Mars accreted in the first ~4 Myr of solar
system formation, which coincides with the formation and possible migration of
Jupiter. While nebular gas from the protoplanetary disk was still present,
Jupiter may have migrated inwards and tacked at 1.5 AU in a 3:2 resonance with
Saturn. This migration excited planetary building blocks in the inner solar
system, resulting in extensive mixing and planetesimal removal. Here we
evaluate the plausible nature of Mars' building blocks, focusing in particular
on how its growth was influenced by the formation and migration of Jupiter. We
use a combination of dynamical simulations and an isotopic mixing model that
traces the accretion of elements with different affinities for metal. Dynamical
simulations show that Jupiter's migration causes the late stages of Earth's and
Mars' accretion to be dominated by EC-type (enstatite chondrite) material due
to the loss of OC (ordinary chondrite) planetesimals. Our analysis of available
isotopic data for SNC meteorites shows that Mars consists of approximately
68%$^{+0}_{-39}$ EC + 32%$^{+35}_{-0}$ OC by mass (2{\sigma}). The large
uncertainties indicate that isotopic analyses of martian samples are for the
most part too imprecise to definitely test model predictions; in particular it
remains uncertain whether or not Mars accreted predominantly EC material in the
latter stages of its formation history. Dynamical simulations also provide no
definitive constraint on Mars' accretion history due to the great variety of
dynamical pathways that the martian embryo exhibits. The present work calls for
new measurements of isotopic anomalies in SNC meteorites targeting siderophile
elements (most notably Ni, Mo and Ru) to constrain Mars' accretion history and
its formation location.
