The curious case of Mars formation

Abstract

Dynamical models of planet formation coupled with cosmochemical data from martian meteorites show that Mars' isotopic composition is distinct from that of Earth. Reconciliation of formation models with meteorite data require that Mars grew further from the Sun than its present position. Here, we evaluate this compositional difference in more detail by comparing output from two $N$-body planet formation models. The first of these planet formation models simulates what is termed the "Classical" case wherein Jupiter and Saturn are kept in their current orbits. We compare these results with another model based on the "Grand Tack", in which Jupiter and Saturn migrate through the primordial asteroid belt. Our estimate of the average fraction of chondrite assembled into Earth and Mars assumes that the initial solid disk consists of only sources of enstatite chondrite composition in the inner region, and ordinary chondrite in the outer region. Results of these analyses show that both models tend to yield Earth and Mars analogues whose accretion zones overlap. The Classical case fares better in forming Mars with its documented composition (29% to 68% enstatite chondrite plus 32% to 67% ordinary chondrite) though the Mars analogues are generally too massive. However, if we include the restriction of mass on the Mars analogues, the Classical model does not work better. We also further calculate the isotopic composition of ${}^{17}\mathrm{O}$, ${}^{50}\mathrm{Ti}$, ${}^{54}\mathrm{Cr}$, ${}^{142}\mathrm{Nd}$, ${}^{64}\mathrm{Ni}$, and ${}^{92}\mathrm{Mo}$ in the martian mantle from the Grand Tack simulations. We find that it is possible to match the calculated isotopic composition of all the above elements in Mars' mantle with their measured values, but the resulting uncertainties are too large to place good restriction on the early dynamical evolution and birth place of Mars.

14 pages, 8 figures, presented in the 2017 DPS meeting, 2018 Solar system symposium in Sapporo and 2018 AOGS annual meeting, Accepted for publishing in A&A

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Cited by in corpus (11)

• Onset of giant planet migration before 4480 million years ago
• Jupiter's influence on the building blocks of Mars and Earth
• Growing Mars fast: High-resolution GPU simulations of embryo formation
• The terrestrial planet formation paradox inferred from high-resolution N-body simulations
• Isotopically distinct terrestrial planets via local accretion
• Mars in the aftermath of a colossal impact
• Mars' formation can constrain the primordial orbits of the gas giants
• Accretion regions of meteorite parent bodies inferred from a two-endmember isotopic mixing model
• Terrestrial planet formation during giant planet formation and giant planet migration I: The first 5 million years
• Constraining the Origin of Mars via Simulations of Multi-Stage Core Formation
• Evidence of a primordial isotopic gradient in the inner region of the solar protoplanetary disc