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The Capture of Interstellar Objects by our Solar System

Presentation #227.07 in the session The Sun and Solar System I.

Published onJun 29, 2022
The Capture of Interstellar Objects by our Solar System

Motivated by recent visits from interstellar objects ”Oumuamua and Borisov, we study the capture of bodies on initially hyperbolic orbits by our solar system. Using an ensemble of 500 million numerical experiments, we generalize previous treatments by calculating the capture cross section as a function of asymptotic speed. The cross section can be convolved with any distribution of relative speeds to determine the capture rate for incoming bodies. To complement our numerical experiment, we construct an analytic description of the capture process that provides an explanation for the functional form of the capture cross section in both the high velocity and low velocity limits. We then use an ensemble of N-body simulations to characterize a dynamical lifetime for captured interstellar objects and determine the surviving fraction as a function of time since capture. We investigate the primary effects driving the objects’ secular evolution, and find that the von Ziepel-Lidov-Kozai effect acts as a phase-protection mechanism, allowing a small fraction of captured objects to avoid close encounters with the giant planets and survive for Gyr timescales. 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 ~10-13 M, whereas the mass remaining from capture events in the birth cluster is roughly 10-9M.

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