Implantation of asteroids from the terrestrial planet region: The effect of the timing of the giant planet instability

TL;DR

This study investigates how the timing of giant planet instability influences the implantation of terrestrial planetesimals into the asteroid belt, using numerical simulations to match observed asteroid belt characteristics.

Contribution

It demonstrates that a giant planet instability occurring after 5 million years aligns with the current asteroid belt's composition and mass distribution.

Findings

Instability after 5 Myr matches asteroid belt observations.

Early instability (<5 Myr) is inconsistent with the asteroid belt scenario.

Timing of instability affects asteroid implantation efficiency.

Abstract

The dynamical architecture and compositional diversity of the asteroid belt strongly constrain planet formation models. Recent Solar System formation models have shown that the asteroid belt may have been born empty and later filled with objects from the inner ($<$2~au) and outer regions (>5 au) of the solar system. In this work, we focus on the implantation of inner solar system planetesimals into the asteroid belt - envisioned to represent S and/or E- type asteroids - during the late-stage accretion of the terrestrial planets. It is widely accepted that the solar system's giant planets formed in a more compact orbital configuration and evolved to their current dynamical state due to a planetary dynamical instability. In this work, we explore how the implantation efficiency of asteroids from the terrestrial region correlates with the timing of the giant planet instability, which has proven challenging to constrain. We carried out a suite of numerical simulations of the accretion of terrestrial planets considering different initial distributions of planetesimals in the terrestrial region and dynamical instability times. Our simulations show that a giant planet dynamical instability occurring at $t\gtrapprox5$ Myr -- relative to the time of the sun's natal disk dispersal -- is broadly consistent with the current asteroid belt, allowing the total mass carried out by S-complex type asteroids to be implanted into the belt from the terrestrial region. Finally, we conclude that an instability that occurs coincident with the gas disk dispersal is either inconsistent with the empty asteroid belt scenario, or may require that the gas disk in the inner solar system have dissipated at least a few Myr earlier than the gas in the outer disk (beyond Jupiter's orbit).