Analysis of terrestrial planet formation by the Grand Tack model: System architecture and tack location

TL;DR

This study evaluates the Grand Tack model of terrestrial planet formation through extensive N-body simulations, finding that a tack location at 2 AU better explains the observed inner solar system than 1.5 AU, especially under oligarchic initial conditions.

Contribution

It provides a comprehensive analysis of how different tack locations and initial conditions affect terrestrial planet formation, favoring a farther-out tack at 2 AU for better alignment with observations.

Findings

A tack at 1.5 AU is inconsistent with the observed planet distribution.

A tack at 2 AU better reproduces the mass and orbital architecture of terrestrial planets.

Oligarchic initial conditions more accurately match the solar system's features.

Abstract

The Grand Tack model of terrestrial planet formation has emerged in recent years as the premier scenario used to account for several observed features of the inner solar system. It relies on early migration of the giant planets to gravitationally sculpt and mix the planetesimal disc down to ~1 AU, after which the terrestrial planets accrete from material left in a narrow circum-solar annulus. Here we have investigated how the model fares under a range of initial conditions and migration course-change (`tack') locations. We have run a large number of N-body simulations with a tack location of 1.5 AU and 2 AU and tested initial conditions using equal mass planetary embryos and a semi-analytical approach to oligarchic growth. We make use of a recent model of the protosolar disc that takes account of viscous heating, include the full effect of type 1 migration, and employ a realistic mass-radius relation for the growing terrestrial planets. Results show that the canonical tack location of Jupiter at 1.5 AU is inconsistent with the most massive planet residing at 1 AU at greater than 95% confidence. This favours a tack farther out at 2 AU for the disc model and parameters employed. Of the different initial conditions, we find that the oligarchic case is capable of statistically reproducing the orbital architecture and mass distribution of the terrestrial planets, while the equal mass embryo case is not.