Evidence for the Presence of Thin and Heterogenous Dust Deposits on Ryugu's Boulders From Hayabusa2 MARA and Sample Data

Abstract

Middle infrared spectral results obtained in-situ by the Hayabusa2 MARA instrument are generally in-line with previous results and a new comparison with sample C0137 returned from asteroid (162173) Ryugu, being similar to an aqueously altered CI1 chondrite. The mid-IR spectrum of the boulder on Ryugu measured by MARA is shallower around 9 μm compared to the laboratory spectrum of C0137. Here we show that discontinuous, fine dust deposits can partially explain the differences in the spectral data and remain in agreement with the temperature observations of the boulder by MARA if an opaque dust layer covers less than 3% of the field of view. Such a presence of dust covering a low porosity boulder was discounted by previous analysis of the mid-infrared MARA data which did not consider a highly porous boulder as we do here.