The meteoroid stream of comet Encke at Mercury: Implications for MErcury Surface, Space ENvironment, GEochemistry, and Ranging observations of the exosphere

Abstract

Abstract We test the hypothesis that an annually repeatable Ca emission excess in Mercury's exosphere at a True Anomaly Angle (TAA) of 25° ± 5° is due to particles from comet 2P/Encke impacting the surface. By simulating the dynamical evolution of Encke particles under planetary perturbations and Poynting‐Robertson drag, we find that millimeter‐sized grains ejected 1–2 ×10 4 years ago encounter Mercury at TAA = 350°–30°. The timing of the excess emission is consistent with a major dust release episode 20 kyr ago, possibly due to Encke progenitor breakup. The emission mechanism is likely the direct injection of impact‐liberated Ca into sunlight rather than nightside surface adsorption for subsequent release at dawn. The timing of dust release from the comet depends on this mechanism; a 10 kyr age is implied by the direct‐injection scenario.