Mars' formation can constrain the primordial orbits of the gas giants

TL;DR

This study uses high-resolution simulations to explore how the primordial orbits of Jupiter and Saturn influenced Mars's rapid formation and accretion zone, suggesting more circular early orbits for the gas giants.

Contribution

It provides new insights into the early orbital configurations of Jupiter and Saturn by linking accretion zones with planetary formation timescales and isotopic data.

Findings

CJS (circular orbits) better matches isotopic mixing models.

EJS (eccentric orbits) results in similar accretion zones for Mars and Earth.

More circular early orbits of gas giants are supported during gas disc dissipation.

Abstract

Recent high precision meteoritic data infers that Mars finished its accretion rapidly within 10 Myr of the beginning of the Solar system and had an accretion zone that did not entirely overlap with the Earth's. Here we present a detailed study of the accretion zone of planetary embryos from high resolution simulations of planetesimals in a disc. We found that all simulations with Jupiter and Saturn on their current eccentric orbits (EJS) result in a similar accretion zone between fast-forming Mars and Earth region embryos. Assuming more circular orbits for Jupiter and Saturn (CJS), on the other hand, has a significantly higher chance of forming Mars with an accretion zone not entirely dominated by Earth and Venus region embryos, however CJS in general forms Mars slower than in EJS. By further quantifying the degree of overlap between accretion zones of embryos in different regions with the average overlap coefficient (OVL), we found that the OVL of CJS shows a better match with the OVL from a chondritic isotopic mixing model of Earth and Mars, which indicates that the giant planets are likely to have resided on more circular orbits than today during gas disc dissipation, matching their suggested pre-instability orbits. More samples, including those from Mercury and Venus, could potentially confirm this hypothesis.