The Distribution of Earth-impacting Interstellar Objects

Abstract

In this paper we calculate the expected orbital elements, radiants, and velocities of Earth-impacting interstellar objects. We generate a synthetic population of ∼1010 interstellar objects with M-star kinematics in order to obtain ∼104 Earth impactors. The relative flux of impactors arriving from the direction of the solar apex and the Galactic plane is enhanced by a factor of ∼2 relative to the mean. The fastest impactors also arrive from these directions, although Earth impactors are generally slower than objects in the overall population. This is because the Earth-impacting subset contains a higher fraction of low-eccentricity hyperbolic objects, which are more strongly affected by gravitational focusing. Earth-impacting interstellar objects are more likely to have retrograde orbits close to the ecliptic plane. A selection effect makes the inclination distribution of Earth-impacting interstellar objects uniform (sinusoidal) at low (high) perihelion distances. In turn, low-perihelion impactors have a higher impact probability towards the ecliptic plane. The overall impactor population therefore exhibits an intermediate inclination distribution between uniform and sinusoidal. In turn, low-perihelion impactors have a higher impact probability towards the ecliptic plane. The highest-velocity impacts are most likely to occur in the spring when the Earth is moving towards the solar apex. However, impacts in general are more likely to occur during the winter when the Earth is located in the direction of the antapex. Interstellar objects are more likely to impact the Earth at low latitudes close to the equator, with a slight preference for the Northern Hemisphere due to the location of the apex. These distributions are independent of the assumed interstellar object number density, albedos, and size frequency distribution and are publicly available.