Dynamical erosion of the asteroid belt and implications for large impacts in the inner solar system

TL;DR

This study models the long-term dynamical erosion of the asteroid belt, revealing a significant depletion over billions of years and a corresponding decline in impact rates on Earth, with implications for planetary impact hazard assessments.

Contribution

It introduces a logarithmic decay model for asteroid loss due to chaos, providing new insights into the depletion history and impact flux of large asteroids in the inner solar system.

Findings

Up to 50% of large asteroids lost since 1 My after belt formation.

Impact probability of ~0.3% for asteroids escaping the belt.

Current impact flux is about ten times lower than previous estimates.

Abstract

The cumulative effects of weak resonant and secular perturbations by the major planets produce chaotic behavior of asteroids on long timescales. Dynamical chaos is the dominant loss mechanism for asteroids with diameters D > 10 km in the current asteroid belt. In a numerical analysis of the long term evolution of test particles in the main asteroid belt region, we find that the dynamical loss history of test particles from this region is well described with a logarithmic decay law. In our simulations the loss rate function that is established at t = 1 My persists with little deviation to at least t = 4 Gy. Our study indicates that the asteroid belt region has experienced a significant amount of depletion due to this dynamical erosion - having lost as much as ~50% of the large asteroids - since 1 My after the establishment of the current dynamical structure of the asteroid belt. Because the dynamical depletion of asteroids from the main belt is approximately logarithmic, an equal amount of depletion occurred in the time interval 10-200 My as in 0.2-4 Gy, roughly ~30% of the current number of large asteroids in the main belt over each interval. We find that asteroids escaping from the main belt due to dynamical chaos have an Earth impact probability of ~0.3%. Our model suggests that the rate of impacts from large asteroids has declined by a factor of 3 over the last 3 Gy, and that the present-day impact flux of D > 10 km objects on the terrestrial planets is roughly an order of magnitude less than estimates currently in use in crater chronologies and impact hazard risk assessments.