Compositional Interpretation of PFS/MEx and TES/MGS Thermal Infrared Spectra of Phobos

The origin of the Martian satellites presents a puzzle of long standing. Addressing the composition of Phobos will help constrain theories of its formation. Visible and near-infrared spectra of Phobos lack of deep absorption features, making the compositional interpretation a tricky task. PFS/MEx and TES/MGS observations in the thermal infrared show several spectral features that can be used to investigate the composition of the surface. Our results show that the majority of the spectra are consistent with a dominance of phyllosilicate. Some spectra also suggest the presence of Feldspars/Feldspathoids. The spectral compositional results suggest ultramafic assemblages. Unexpectedly, comparison of the TES and PFS data to the meteorites shows that no class of chondrites provide significant agreement with the spectral features observed.