Encounter circumstances of asteroid 99942 Apophis with the catalogue of known asteroids

Abstract

Asteroid 99942 Apophis will pass near the Earth in April 2029. Expected to miss our planet by a safe margin, that could change if Apophis' path was perturbed by a collision with another asteroid in the interim. Though the statistical chance of such a collision is minuscule, the high risk associated with Apophis motivates us to examine even this very unlikely scenario. In this work, we identify encounters between known asteroids and Apophis up to April 2029. Here we show that Apophis will encounter the 1300 meter diameter asteroid 4544 Xanthus in December 2026. Their Minimum Orbit Intersection Distance (MOID) is less than 10,000 km, with Xanthus passing that closest point just four hours after Apophis. Though a direct collision is ruled out, the encounter is close enough that material accompanying Xanthus (if any) could strike Apophis. We also identify other asteroid encounters that deserve monitoring.