Impact processes on asteroids and planets are an essential part of the evolution of the solar system. Rocks ejected from celestial objects by such impacts can encounter Earth and fall as meteorites, carrying with them information about their parent bodies including record of impacts. In particular, transient dynamic compression causes shock metamorphism, preserved as nanoscale high-pressure phases in meteorites that can reveal the conditions of their corresponding planetary impacts. Eleanor and John R. McMillan Professor of Geology and Geochemistry Paul Asimow and his group use focused-ion beam sample preparation and transmission electron microscopy in the KNI to characterize these nanophases in both meteorites and in our shock compression experiments, in order to shed light on the record of impacts that accompanied the evolution of the solar system to its current state.
In shocked meteorites, all the common planet-forming mineral groups may show transformations due to shock metamorphism, including silicates, oxides and metals. The common low-pressure silicate olivine, for instance, is transformed in both asteroidal and martian meteorites to spinel structures, which are thought to the predominant phases in the Earth's mantle between 410 and 660 km depth . In metallic systems, the recent discovery of meteoritical quasicrystals has motivated novel collaboration among physicists, material scientists and geologists. This work has not only demonstrated a new formation mechanism for quasicrystals and even new quasicrystal-forming chemical systems but also revealed the occurrence of surprisingly reduced Al-Cu-Fe-Ni metal alloys in the early solar system .
Our ongoing and future projects are aimed at shock-induced changes in the volatile element (H, C, N, noble gases) in Martian meteorites. We use these meteorites to trace the evolution of the Martian atmosphere and lithosphere, but how strongly modified is this record by the shock of ejection from Mars? The combination of the Asimow group shock experimental platform and KNI's nanoanalysis capabilities can address how volatiles and potentially habitable zones evolved on ancient Mars.
 Baziotis I, Asimow PD, Hu J, Ferrière L, Ma C, Cernok A, Anand M, Topa D (2018) High pressure minerals in the Château-Renard (L6) ordinary chondrite: implications for collisions on its parent body. Sci Rep Nature Publishing Group8(1): 9851
 Oppenheim J, Ma C, Hu J, Bindi L, Steinhardt PJ, Asimow PD (2017) Shock Synthesis of Decagonal Quasicrystals. Scientific Reports 7(1): 15628
Left image: Electron diffraction pattern of topotaxial silicate spinels from the Château-Renard meteorite . Rigth Images: (a) TEM image of shock-synthesized decagonal quasicrystal ; (b, c) Electron diffraction of 10-fold rotation axis of decagonite. Data collected on Nova 600 Dual-beam FIB and TF-20 TEM at KNI.