Surface rejuvenation of near-Earth asteroids triggered by planetary shadows

Abstract Near-Earth asteroids (NEAs) are small, airless bodies that orbit in near-Earth space. Recent studies suggest that surface rocks on NEAs can undergo crack growth and fragmentation due to mechanical stresses induced by diurnal temperature cycling. This thermal fatigue process has the potential to rejuvenate asteroid surfaces that have aged due to solar wind irradiation and micrometeorite impacts. However, the mechanism by which initial cracks are generated as a trigger for thermal fatigue fragmentation is not well understood. Here we show that NEAs can experience rapid temperature changes sufficient to generate microcracks in surface rocks as they pass through the shadow of a terrestrial planet. Our statistical analysis of backward orbital integrations demonstrates that NEAs pass through planetary shadows more often than they encounter planets at distances where planetary tides become effective. We also found that the duration of shadow passages is shorter than the average spin period of asteroids, indicating that expansion stress from rapid heating occurs immediately after contraction stress from rapid cooling. These results suggest that thermal shock caused by planetary shadows may play a key role in triggering surface rejuvenation of NEAs.