Reactive molecular dynamics simulations of micrometeoroid bombardment for space weathering of asteroid (162173) Ryugu

TL;DR

This study uses reactive molecular dynamics simulations to show that micrometeoroid impacts can cause dehydration and hydroxyl formation on asteroid Ryugu, significantly contributing to space weathering processes.

Contribution

First simulation-based analysis quantifying micrometeoroid impact effects on asteroid surface chemistry during space weathering.

Findings

Micrometeoroids as small as 2 nm can dehydroxylate serpentine.

Nano-sized dust impacts increase hydroxyl dissociation by an order of magnitude.

Impacts generate Si-OH, H2O, and free OH, affecting asteroid surface composition.

Abstract

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, ~200 O-H bonds dissociated when the meteoroids were derived from cometary activity (the impact velocity was ~20 km s$^{-1}$). When nano-sized dust particles were accelerated to ~300 km s$^{-1}$ by the magnetic fields of solar wind plasma, the number of dissociated O-H bonds increased by one 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 time scale to 1 ps, reactive molecular dynamic simulations demonstrated that micrometeoroid bombardment could influence the space weathering of asteroids.