Surface rejuvenation of stony near-Earth asteroids triggered by planetary shadows
Kohei Kitazato, Sho Sakurai, Ryuki Hyodo & Naru Hirata
Nature Geoscience, Published: 15 January 2026
“Near-Earth asteroids (NEAs) are small, airless bodies that orbit in near-Earth space. Recent studies suggest that their surface rocks can undergo crack growth and fragmentation through thermal fatigue induced by diurnal temperature cycling. This process may expose materials yet to be altered by solar wind irradiation and micrometeorite impacts, known as surface rejuvenation. However, the mechanism that generates the initial cracks required to trigger thermal fatigue fragmentation remains poorly understood despite its importance for understanding the geophysical evolution of asteroids. Here we use numerical approaches to show that stony, or S-complex NEAs, the most compositionally common group, can experience rapid temperature changes, or thermal shocks, 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 these asteroids pass through planetary shadows more often than they encounter planets closely enough for planetary tides to rejuvenate their surfaces. We also found that shadow passages are shorter than typical asteroid spin periods, 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 help trigger the surface rejuvenation of stony NEAs.”
