Mechanochemistry in Space Promoted by Nanometeoroid Bombardment on an Asteroid

 

In the universe, phenomena occur that depend on micro- and nano-sized particles that, accelerated by the interplanetary magnetic field, impact and transform celestial bodies, producing surface changes—a process known as space weathering.

In 2018-2019, Japan's Hayabusa2 spacecraft obtained in situ infrared reflectance spectra of the surface of asteroid (162173) Ryugu, which showed an absorption band at ~2.7 μm corresponding to O-H vibrations in the asteroid’s phyllosilicates.

Through a directed impact, the Hayabusa2 spacecraft created a crater approximately 1 m deep on the asteroid’s surface. The infrared reflectance spectra near the crater revealed a more intense absorption band at ~2.7 μm, suggesting that the asteroid’s surface underwent a dehydration process (dissociation of O-H bonds).

To study the dissociation mechanism of these chemical bonds, the authors of this study used simulation methods with reactive molecular dynamics. The model simulated the bombardment of the asteroid’s phyllosilicates with impactors of fixed diameters (1 or 2 nm). In the absence of the magnetic fields of the interplanetary solar wind plasma, nanometeoroid impact velocities ranged from 10 to 20 km/s, leading to the dissociation of approximately 200 O-H bonds in the phyllosilicates. When the impactor was accelerated by the interplanetary magnetic field, impact velocity increased by an order of magnitude (up to ~300 km/s), dissociating over 1000 O-H bonds even with nanometeoroids of 1 nm in diameter.

The dehydration of the asteroid’s surface minerals was attributed to the kinetic energy of the impacts, which caused local heating exceeding 1000 Kelvin at the impact site.

This discovery contributes to understanding the evolution of asteroid chemical composition and the role of nanometeoroids in the interplanetary medium.

For more information, consult The Astrophysical Journal