Detection of nanostructured metal in meteorites: implications for the reddening of asteroids

The association between the most abundant population of meteorites, the ordinary chondrites, and their parent bodies is one of the main topics in the quest to understand the evolution of the solar system. This association is mainly inferred from spectra in visible and near-infrared wavelengths, where many of the asteroids show reddened reflected light curves. The analysis of lunar soils attributed the reddening of the spectra to the presence of nanometer-size metallic particles, and a simulation of micrometeoroid impacts with laser irradiation experiments on terrestrial samples has reproduced this effect and tied it to the vaporization of Fe-bearing silicates. Recently, spacecraft observations have revealed a new mystery in the interpretation of the reddening of S-type asteroids. We have identified an alternative process for surface alteration of airless bodies that can be invoked to solve this mystery through a shock-induced phase transformation of Fe-Ni alloys. These metal phases are usually reported in meteorites but have never been associated with the reddening of the spectra. Here we show, for the first time, atomic force microscopy observations of diffuse nanostructured metal in ordinary chondrites. We also show that the corresponding spectra are unambiguously redder.