Sodium-rich Particle as Evidence of Recent and Intense Micrometeoroid Bombardment on Asteroid RyuguOPEN ACCESS 

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E. Palomba, G. Pratesi, M. Angrisani, X. Shehaj, F. Dirri, A. Longobardo, D. Fulvio, S. Caporali, and B. Cortigiani

The Astrophysical Journal Letters, Volume 1001, Number 1, Published 2 April 2026

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“The Hayabusa2 spacecraft returned regolith particles of the near-Earth asteroid Ryugu. We investigated two of these particles and found differences in space weathering by-products, including chemical abundance, redox state, and surface morphology. The more weathered particle shows widespread evidence of microimpacts and, within its outermost surface layers (<10 nm), a pronounced enrichment in sodium (a volatile element), likely vapor deposited during micrometeoroid impacts. The preservation of this ultrathin volatile-rich layer in the harsh space environment suggests that Ryugu’s surface experienced an intense micrometeoroid bombardment, possibly within the past ∼1000 yr. These findings underscore the role of meteoroid streams and associated outbursts in driving the space weathering of planetary surfaces.”

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