Understanding the modification of solids in space environments by studying regolith samples from asteroids and the Moon

Abstract

Space weathering refers to the alteration of regolith grains on airless bodies caused by solar wind irradiation and micrometeorite bombardment. Analysis of regolith grains from the asteroid Itokawa and Ryugu by the spacecraft Hayabusa and Hayabusa 2 revealed space weathering of various minerals. The widespread occurrence of metallic iron whiskers was found as a decomposition product formed by selective loss of sulfur. Aqueous minerals such as phyllosilicates, carbonates, and magnetite have experienced the escape of water, carbon, and oxygen respectively. Iron nitride on magnetite in Ryugu suggests inorganic nitrogen fixation by micrometeorite impact. These studies suggest that the behavior of volatile elements through space weathering is deeply involved in the chemical evolution of small bodies in the Solar System.