Primitive extraterrestrial materials, such as meteorites and dust collected by sample return missions, are characterized by a large compositional heterogeneity at different scales. This heterogeneity has been observed in the laboratory by different techniques. Among these, micro-IR spectroscopy has the advantage of being totally non-destructive and allowing direct comparison with astronomical observations. With the development of Focal Plan Array detectors, IR mapping with high spatial resolution and IR tomography is now possible with a short acquisition time. In this presentation I will show some recent results of FTIR spectral imaging experiments on different extraterrestrial materials, obtained at SMIS – Synchrotron SOLEIL (France), and the implementation of an analytical protocol for future sample return missions.
I will also present new VIS-IR spectral imaging data of ion irradiated meteorites, simulating solar wind irradiation of asteroid surfaces. Together with direct evidence of weathering of asteroid Itokawa particles collected by Hayabusa, these results contribute to the spectral interpretation of asteroid observations, to establish a solid asteroids-meteorites link, and to understand the energetic processes affecting the surfaces of minor bodies. Micro-spectral imaging allows characterizing the heterogeneity of meteorites at the 20 µm spatial scale. In laboratory-irradiated samples, we observe spectral modifications of the phyllo-silicates, anhydrous silicates, carbonates, water, and organic materials features, as well as variations in the albedo. Compositional heterogeneity of the pristine materials and irradiation effects are compared to each other as a function of the irradiation dose, to determine which spectral features are more sensitive to space weathering. Results are then compared with the spectral capabilities of instruments onboard the Hayabusa 2 (JAXA) and OSIRIS-REx (NASA) spacecraft, to provide these missions with spectral criteria on how to distinguish weathering from compositional heterogeneity at the asteroid, and in view of surface selection for sample return.
