Polar orbits around the newly formed Earth-Moon binary system

Abstract

We examine the dynamics and stability of circumbinary particles orbiting around the Earth-Moon binary system. The moon formed close to the Earth (semi-major axis $a_{EM}\approx 3R_{\oplus }$) and expanded through tides to its current day semi-major axis ($a_{EM}=60R_{\oplus }$). Circumbinary orbits that are polar or highly inclined to the Earth-Moon orbit are subject to two competing effects: (i) nodal precession about the Earth-Moon eccentricity vector and (ii) Kozai-Lidov oscillations of eccentricity and inclination driven by the Sun. While we find that there are no stable polar orbits around the Earth-Moon orbit with the current day semi-major axis, polar orbits were stable immediately after the formation of the Moon, at the time when there was a lot of debris around the system, up to when the semi-major axis reached about $a_{EM}\approx 10R_{\oplus }$. We discuss implications of polar orbits on the evolution of the Earth-Moon system and the possibility of polar orbiting moons around exoplanet-moon binaries.

Accepted for ApJ