Probing the early stages of shock-induced chondritic meteorite formation at the mesoscale

Abstract

Chondritic meteorites are fragments of asteroids, the building blocks of planets, that retain a record of primordial processes. Important in their early evolution was impact-driven lithification, where a porous mixture of millimetre-scale chondrule inclusions and sub-micrometre dust was compacted into rock. In this Article, the shock compression of analogue precursor chondrite material was probed using state of the art dynamic X-ray radiography. Spatially-resolved shock and particle velocities, and shock front thicknesses were extracted directly from the radiographs, representing a greatly enhanced scope of data than could be measured in surface-based studies. A statistical interpretation of the measured velocities showed that mean values were in good agreement with those predicted using continuum-level modelling and mixture theory. However, the distribution and evolution of wave velocities and wavefront thicknesses were observed to be intimately linked to the mesoscopic structure of the sample. This Article provides the first detailed experimental insight into the distribution of extreme states within a shocked powder mixture, and represents the first mesoscopic validation of leading theories concerning the variation in extreme pressure-temperature states during the formation of primordial planetary bodies.

Interrogating heterogeneous compaction of analogue materials at the mesoscale through numerical modeling and experiments

“…This work has investigated the compaction of mixtures analog to precursor meteorite matter through real-time, in-situ, mesoscale, experiments at the ESRF [5] and numerical models using the iSALE shock physics code [6]. Two scenarios were considered, compaction of a pure fine-grained, highly porous granular material analogous to the precursor of meteoritic matrix material and the same material with a single non-porous inclusion of the same composition.…”

“…To provide experimental support for the nature of shock compaction of primitive solids, and investigate the temperature dichotomy, we devised a joint experimental and numerical approach. Experiments were performed at the European Synchrotron Radiation Facility (ESRF) utilising state-of-the-art, in-situ, mesoscale X-ray imaging techniques [5] and numerical models were performed with the shock physics code iSALE [5,6]. The experiments were used to validate iSALE's numerical models which can subsequently be used to investigate experimentally inaccessible features such as temperature or pressure.…”

“…Shots were performed using a 3 m, 12.7 mm bore, single stage light-gas gun aligned perpendicular to the X-ray beam. Radiographs were captured indirectly using a single crystal LYSO scintillator [5] imaged by a pair of PI-MAX4 cameras, each capable of taking two images. The cameras were triggered sequentially such that four radiographs were taken per shot with intervals of 0.878µs, 0.708µs, and 0.878µs between each frame respectively.…”

Ultra high-speed x-ray imaging of laser-driven shock compression using synchrotron light

“…Synchrotron x-ray pulses have ≈100 ps full-width-athalf-maximum (FWHM); when combined with an imaging detector with 10 μm spatial resolution, this gives the possibility to freeze a motion up to a speed of 10 km s −1 (10 mm μs −1 ) [5,32]. XPCI using synchrotron x-rays is becoming widely employed for impact-driven shock experiments using gas guns [5,6,33]. The Advanced Photon Source in the USA has, for several years, been performing time-resolved XRD and XPCI gas-gun experiments with emphasis on condensed matter and materials science activities [5].…”

“…The Advanced Photon Source in the USA has, for several years, been performing time-resolved XRD and XPCI gas-gun experiments with emphasis on condensed matter and materials science activities [5]. At the ESRF and the Diamond Light Source in the UK, time-resolved XRI on gas-gun experiments have been performed to study asteroid impacts [6,33]. XPCI has provided the measurements of mechanical wave speed and density changes, and the understanding of shock-induced macroscopic processes leading to deformations and failure.…”