Pyroxenes microstructure in comet 81P/Wild 2 terminal Stardust particles

Authors


damien.jacob@univ-lille1.fr

Abstract

Abstract— We report the examination by transmission electron microscopy (TEM) of four Stardust terminal particles extracted from two neighboring tracks (32 an 69). The particles are made of well-preserved crystalline grains dominated by low-Ca pyroxene ranging from nearly pure enstatite to pigeonite. Some olivine grains are also found, in chemical equilibrium with the surrounding pyroxenes. Various microstructures are observed, as a function of the composition of the grains. They include (100)-twinned pigeonite, clino/ortho domains in enstatite and exsolution in a Ca-rich grain. The microstructures are mostly consistent with a formation by cooling from high-temperature phases, which could be associated to igneous processes. Some dislocations in glide configuration are also present, probably attesting for small intensity shocks. Possible effects of the rapid heating/cooling stage and thermal shock associated to the collect are discussed. It appears that most of the microstructural features reported here are plausibly pristine.

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