On the Fate of Interstellar Objects Captured by our Solar System

TL;DR

This paper investigates the capture and longevity of interstellar objects in our solar system using simulations, estimating the current amount of captured interstellar material and its dynamical evolution.

Contribution

It introduces a method to calculate capture cross sections and dynamical lifetimes of interstellar objects, providing new estimates of their current abundance in the solar system.

Findings

Capture from the field results in a very small steady state mass (~10^-13 Earth masses).

Capture from the birth cluster yields a higher mass (~10^-9 Earth masses).

Dynamical simulations reveal key factors influencing the evolution and survival of captured objects.

Abstract

With the recent discoveries of interstellar objects `Oumuamua and Borisov traversing the solar system, understanding the dynamics of interstellar objects is more pressing than ever. These detections have highlighted the possibility that captured interstellar material could be trapped in our solar system. The first step in rigorously investigating this question is to calculate a capture cross section for interstellar objects as a function of hyperbolic excess velocity, which can be convolved with any velocity dispersion to compute a capture rate (Napier et. al. 2021). Although the cross section provides the first step toward calculating the mass of alien rocks residing in our solar system, we also need to know the lifetime of captured objects. We use an ensemble of N-body simulations to characterize a dynamical lifetime for captured interstellar objects and determines the fraction of surviving objects as a function of time (since capture). We also illuminate the primary effects driving their secular evolution. Finally, we use the resulting dynamical lifetime function to estimate the current inventory of captured interstellar material in the solar system. We find that capture from the field yields a steady state mass of only $\sim 10^{-13} M_{\oplus}$, whereas the mass remaining from capture events in the birth cluster is roughly $10^{-9} M_{\oplus}$.