  Many dynamical aspects of the solar system can be explained by the outer
planets experiencing a period of orbital instability sometimes called the Nice
Model. Though often correlated with a perceived delayed spike in the lunar
cratering record known as the Late Heavy Bombardment (LHB), recent work
suggests that this event may have occurred much earlier; perhaps during the
epoch of terrestrial planet formation. While current simulations of terrestrial
accretion can reproduce many observed qualities of the solar system,
replicating the small mass of Mars requires modification to standard planet
formation models. Here we use 800 dynamical simulations to show that an early
instability in the outer solar system strongly influences terrestrial planet
formation and regularly yields properly sized Mars analogs. Our most successful
outcomes occur when the terrestrial planets evolve an additional 1-10 million
years (Myr) following the dispersal of the gas disk, before the onset of the
giant planet instability. In these simulations, accretion has begun in the Mars
region before the instability, but the dynamical perturbation induced by the
giant planets' scattering removes large embryos from Mars' vicinity. Large
embryos are either ejected or scattered inward toward Earth and Venus (in some
cases to deliver water), and Mars is left behind as a stranded embryo. An early
giant planet instability can thus replicate both the inner and outer solar
system in a single model.
