Reactive Molecular Dynamics Simulations of Micrometeoroid Bombardment for Space Weathering of Asteroid (162173) Ryugu

D Shoji, ASTROPHYSICAL JOURNAL, 973, 13 (2024).

DOI: 10.3847/1538-4357/ad70b0

Remote sensing observations by Hayabusa2 and laboratory measurements have revealed that the phyllosilicates on asteroid (162173) Ryugu are dehydrated/dehydroxylated due to space weathering. Reactive molecular dynamics simulations were performed to evaluate the magnitude of the dehydroxylation of Mg-rich serpentine by micrometeoroid impacts. When micrometeoroids were not coupled with interplanetary magnetic fields, serpentine could be dehydroxylated by micrometeoroids as small as 2 nm in size. In particular, similar to 200 O-H bonds dissociated when the meteoroids were derived from cometary activity (the impact velocity was similar to 20 km s-1). When nano-sized dust particles were accelerated to similar to 300 km s-1 by the magnetic fields of solar wind plasma, the number of dissociated O-H bonds increased by 1 order of magnitude. Consequently, even 1 nm-sized dust particles can contribute to the space weathering of Ryugu. In all cases, Si-OH, H2O, and free OH were generated from the hydroxyls initially connected to Mg, which could partially offset dehydration. Despite the limitations of our computational resources, which restricted the simulation timescale to 1 ps, reactive molecular dynamic simulations demonstrated that micrometeoroid bombardment could influence the space weathering of asteroids.

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