Formation of the Terrestrial Planets from a Narrow Annulus

TL;DR

This study demonstrates that modeling the formation of terrestrial planets from a narrow initial mass distribution between 0.7 and 1.0 AU can reproduce the observed planetary system's architecture, eccentricities, and formation timescales.

Contribution

It introduces a model where all terrestrial planet mass starts in a narrow annulus, successfully matching observed planetary characteristics without requiring remnant small bodies.

Findings

Mercury and Mars analogues form from collisional evolution.

Final planetary systems match observed eccentricities and inclinations.

Earth analogues form rapidly, consistent with isotopic data.

Abstract

We show that the assembly of the Solar System terrestrial planets can be successfully modelled with all of the mass initially confined to a narrow annulus between 0.7 and 1.0 AU. With this configuration, analogues of Mercury and Mars often form from the collisional evolution of material diffusing out of the annulus under the scattering of the forming Earth and Venus analogues. The final systems also possess eccentricities and inclinations that match the observations, without recourse to dynamical friction from remnant small body populations. Finally, the characteristic assembly timescale for Earth analogues is rapid in this model, and consistent with cosmochemical models based on the $^{182}$Hf--$^{182}$W isotopes. The agreement between this model and the observations suggests that terrestrial planet systems may also be formed in `planet traps', as has been proposed recently for the cores of giant planets in our solar system and others.