Jupiter's influence on the building blocks of Mars and Earth

Abstract

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.