Space Weathering on Carbon-rich Surfaces: Spectral Characterization of Fe-poor Mercury and Carbonaceous Asteroid Analogs

Experimental space weathering efforts and recent sample return analyses have proven that the composition of an airless body plays a distinct role in how its spectra will be altered by space weathering processes. Space weathering on Fe-poor bodies, such as Mercury and a subset of the carbonaceous asteroid population, is not well understood. In an aim to characterize how space weathering may impact the spectra of highly reduced, C-rich regoliths, we simulated aspects of micrometeorite bombardment on 12 analog mixtures featuring low-Fe or Fe-free silicates and carbonaceous opaques with varying levels of graphitization. We present spectral analyses from 0.3–2.5 μm, 4–8 μm, and 8–50 μm (200–1250 cm⁻¹) before and after simulated space weathering. Our investigation shows that carbon-rich materials can darken and redden in the visible-to-near infrared without the presence of nanophase iron, implying that opaques like carbon play a significant role in space weathering of carbon-bearing bodies. The graphitization state of carbon also has clear impacts on spectral features and albedo, which may aid in interpreting what forms of carbon could be present on airless bodies.