Bayesian Inference on the Isotopic Building Blocks of Mars and Earth

Abstract

Isotopic anomalies provide a means of probing the materials responsible for the formation of terrestrial planets. By analyzing new iron isotopic anomaly data from Martian meteorites and drawing insights from published data for O, Ca, Ti, Cr, Fe, Ni, Sr, Zr, Mo, Ru, and Si, we scrutinize potential changes in the isotopic composition of the material accreted by Mars and Earth during their formation. A Principal Component Analysis of isotopic anomalies in meteorites identifies three main clusters (forming the three parts of the isotopic trichotomy): CI, CC=CM+CO+CV+CR, and NC=EH+EL+H+L+LL. Our results suggest that Earth is primarily an isotopic mixture of ~92% E, 6 % CI, and <2% COCV and O. Mars, on the other hand, appears to be a mixture of ~65% E, 33% O, and <2% CI and COCV. We establish that Earth's CI contribution substantially increased during the latter half of its accretion. Mars began accreting a mix of O and E but predominantly accreted E later. Mars' changing isotopic makeup during accretion can be explained if it underwent gas-driven type I migration from its origin near the O - E boundary to a location well within the E region during the first few million years of solar system history. Earth's later increased CI contribution may be attributed to the stochastic impact of an interloper carbonaceous embryo that moved inside the inner solar system region while nebular gas was still present, and subsequently participated in the stage of chaotic growth. The recent findings of Si isotopic anomalies in enstatite chondrites when compared to terrestrial rocks likely stems from insufficient correction for high-temperature equilibrium isotopic fractionation. With appropriate adjustments for this influence, both the silicate Earth and enstatite chondrites exhibit comparable Si isotopic anomalies, reaffirming a genetic link between them.

In press, Icarus

References in corpus (11)

• Building Terrestrial Planets
• Origin of water in the inner Solar System: Planetesimals scattered inward during Jupiter and Saturn's rapid gas accretion
• Abundance, distribution, and origin of 60Fe in the solar protoplanetary disk
• A perspective from extinct radionuclides on a Young Stellar Object: The Sun and its accretion disk
• Terrestrial planet formation from lost inner solar system material
• The Role of Early Giant Planet Instability in the Terrestrial Planet Formation
• Terrestrial planet formation by torque-driven convergent migration of planetary embryos
• Terrestrial planet formation from a ring
• Comparisons of the core and mantle compositions of earth analogs from different terrestrial planet formation scenarios
• Simulations of Protoplanetary Disk Dispersal: Stellar Mass Dependence of the Disk Lifetime
• Isotopic Trichotomy of Main Belt Asteroids from Implantation of Outer Solar System Planetesimals

Cited by in corpus (9)

• Dust-Gas Coupling in Turbulence- and MHD Wind-Driven Protoplanetary Disks: Implications for Rocky Planet Formation
• The cosmochemistry of planetary systems
• Infall and Disk Processes - the Message from Meteorites
• Crash Chronicles: relative contribution from comets and carbonaceous asteroids to Earth's volatile budget in the context of an Early Instability
• Physicochemical Controls on the Compositions of the Earth and Planets
• Early Solar System Turbulence Constrained by High Oxidation States of the Oldest Non-Carbonaceous Planetesimals
• Impact sculpting of the early martian atmosphere
• Homogeneous accretion of the Earth in the inner Solar System
• A Collective Trigger for Widespread Planetesimal Formation Revealed by Accretion Ages