MidIR Spectral Characterization Of Ol-Bearing Ungrouped Achondrites

Sample return missions are at pre- sent one of the primary goals of the Solar System ex- ploration. Different missions addressing that goal are ongoing. Nevertheless, meteorites are a natural sam- pling of our Solar System bodies and they provide im- portant information about their parent bodies, spanning from the most primitive, associated with the origin of our Solar System, to the most evolved ones. Among meteorites, those that have experienced a pro- cess of differentiation are achondrites, and they span from primitive to highly differentiated. They are main- ly composed of mafic minerals and feldspars. Among mafic minerals olivines are expected to be very abundant being the main component of differentiated bodies. However planetary bodies characterized by a clear olivine spectral signature are less than what ex- pected. These objects are often observed in the Visible Near Infrared (VNIR) from Earth or spacecraft, ad- dressing the capability to detect the olivine to the crys- tal field absorption to be attributed mainly to Fe2+ in octahedral coordination. The capability to detect it depends on the abundance of olivine, the mineral asso- ciation (so can change depending which minerals are combine with) and the abundance of iron within a giv- en crystal structure (e.g. [1,2]). Here we investigate the spectral properties of more than 20 ungrouped achondrites with variable mineral association, olivine abundance and olivine composition within the Middle Infrared (MidIR) to evidence how the spectral properties changes in a spectral range where spectroscopy allows recognition of the miner- alogical structures of the shallow crystalline assem- blages. This capability mainly relies upon the charac- teristic spectral features arising from cation–anion and lattice vibrations of crystalline structures in the middle portion of the electromagnetic spectrum [3].