The Taurid Resonant Swarm at Mercury

Abstract

ABSTRACT It has previously been suggested that ejection and vaporization of Hermean surface material by meteoroids from comet 2P/Encke causes a seasonal enhancement in Mercury’s Ca exosphere observed by the NASA MESSENGER spacecraft in 2011-2015. The ESA/JAXA BepiColoen mission, now routeute to Mercury, will likely provide the next set of observational tests of this hypothesis after it enters orbit in late 2025. Here we study the Taurid Swarm Complex (IAU Code: STS), a population of cm-sized or larger meteoroids from Encke’s comet that encounters the Earth every 3–7 yr. Through analysis of previous observations of the STS and many-particle numerical simulations, we study the circumstances of encounters between the STS and Mercury and find that, unlike the Earth where STS encounters is observed in some years but not others, each time the STS is at perihelion it encounters Mercury on three consecutive planetary orbits. We further predict that the STS will encounter this planet during the early stages of BepiColombo’s orbital mission. The temporal flux profile during each encounter will be broad and possibly double-peaked with total number fluence 0.4×–1.7× that of the sporadic fluence for >1 kg meteoroids on the sub-radiant hemisphere of the planet. The meteoroid arrival direction and sub-radiant point strongly depend on True Anomaly Angle, switching from mainly nightside to mainly dayside impacts as Mercury travels from orbital perihelion to aphelion. Our predictions may be used to create detailed models of exosphere generation by Encke stream meteoroids.