Crispy on the Outside, Raw on the Inside: Impact-Induced Melting and Fragmentation of C-Type Asteroid Regolith Documented in a Ryugu Sample

Abstract

The surfaces of airless planetary bodies are continually exposed to hypervelocity impacts of micrometeoroids and influx of solar-wind ions. Collectively known as space weathering, these processes gradually alter the morphologies, microstructures, and chemical compositions of regolith grains exposed to space [1]. Because these changes also affect the optical properties of space-weathered grains [1], understanding space weathering is critical for interpretation of remote-sensing data obtained from airless planetary surfaces and for matching meteorites to parent bodies. While the effects of space weathering on anhydrous regolith materials is well understood and documented in samples returned from the Moon [1, 2] or S-type asteroid Itokawa [3, 4], space weathering of hydrous, carbonaceous chondrite-like (C-type) planetary surfaces is poorly understood. To better understand the role of micrometeoroid impacts in space weathering on C-type asteroids (cf. [5, 6]), we investigated a population of micrometeoroid impact craters on a large regolith particle resembling CI (Ivuna-type) carbonaceous chondrites that was recently returned from C-type asteroid Ryugu by JAXA’s Hayabusa2 mission (e.g., [7]).