Extended Data Fig. 5. 10-nm thick vapor deposit on a smooth layer found in a cross-section sample A104–02809801.
A very thin (~10 nm) layer covers the ~60-nm thick smooth layer. EDS maps show that the upper part of the very thin layer is enriched in Mg, Si, Fe, and O, and the lower part is depleted in Mg, Si, and Fe. There are no detectable differences in concentrations in S and Ni. Because similarly thin top surface layers with such element distribution patterns were reported from Itokawa grains6,7, this top surface layer is considered a vapor deposit on the smooth layer. The estimated boundary between the vapor deposition and the smooth layer is indicated by green or red arrows. This is the only vapor deposit found on the surface of smooth layers investigated.