Lee, J. I. | Search NASA

DOE OSTI2020

Subnanosecond phase transition dynamics in laser-shocked iron

Iron is one of the most studied chemical elements due to its sociotechnological and planetary importance; hence, understanding its structural transition dynamics is of vital interest. By combining a short pulse optical laser and an ultrashort free electron laser pulse, we have observed the subnanosecond structural dynamics of iron from high-quality x-ray diffraction data measured at 50-ps intervals up to 2500 ps. We unequivocally identify a three-wave structure during the initial compression and a two-wave structure during the decaying shock, involving all of the known structural types of iron (α-, γ-, and ε-phase). In the final stage, negative lattice pressures are generated by the propagation of rarefaction waves, leading to the formation of expanded phases and the recovery of γ-phase. Our observations demonstrate the unique capability of measuring the atomistic evolution during the entire lattice compression and release processes at unprecedented time and strain rate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS2019

Genetic Relationship Between Martian Chassignites and Nakhlites Revealed from Noble Gases

A group called as Martian meteorites is composed of shergottites, nakhlites, chassignites, and orthopyroxenite, and they are thought to be derived from Mars. Among the Martian meteorites nakhlites and chassignites show similar cosmic-ray exposure (CRE) ages of 11-12 million years, although petrologic characteristics are very different between them. Both nakhlites and chassignites indicate similar cooling rates, and would have cooled in identical scale of igneous bodies. However, the relationship between nakhlites and chassignites is still unclear, although they might have ejected at the same time, i.e., by accidentally coincidental impact events which occurred at different places on Mars or by a single impact which excavated both nakhlites and chassignites residing in a relatively small area. Here we propose that the chassignites show a genetically close relationship with nakhlites, i.e., both groups could be located within a relatively narrow area from where a single impact could have launched those meteorites, based on noble gas data obtained in our laboratory. If chassignites were really ejected with nakhlites by a single impact, both types of meteorites will provide us with geological/petrological profile in the area where both pyroxene-rich lava (nakhlites) and dunite-rich rocks (chassignites) are located close to the Martian surface. [i.e. discusses NWA 2737, etc. (Martian meteorites that fell in Northwest Africa)]

Nagao, K.↗