Mesoscale Modeling of Impact Compaction of Primitive Solar System Solids

TL;DR

This study presents a mesoscale simulation method for impact compaction of primitive solar system solids, revealing how impact parameters influence shock processing, temperature distribution, and material composition in early solar system materials.

Contribution

The paper introduces a mesoscale modeling approach using iSALE to simulate impact compaction of heterogeneous solar system solids, linking impact parameters to shock effects and material properties.

Findings

Matrix temperatures are significantly higher than chondrules post-impact.

Chondrules can shield parts of the matrix, creating shadow regions with higher porosity.

Post-shock material composition matches meteorite properties.

Abstract

We have developed a method for simulating the mesoscale compaction of early solar system solids in low velocity impact events, using the iSALE shock physics code. Chondrules are represented by nonporous disks, placed within a porous matrix. By simulating impacts into bimodal mixtures over a wide range of parameter space (including the chondrule-to-matrix ratio, the matrix porosity and composition and the impact velocity), we have shown how each of these parameters influences the shock processing of heterogeneous materials. The temperature after shock processing shows a strong dichotomy: matrix temperatures are elevated much higher than the chondrules, which remain largely cold. Chondrules can protect some matrix from shock compaction, with shadow regions in the lee side of chondrules exhibiting higher porosity that elsewhere in the matrix. Using the results from this mesoscale modelling, we show how the $\varepsilon-\alpha$ porous compaction model parameters depend on initial bulk porosity. We also show that the timescale for the temperature dichotomy to equilibrate is highly dependent on the porosity of the matrix after the shock, and will be on the order of seconds for matrix porosities of less than 0.1, and on the order of 10's to 100's seconds for matrix porosities of $\sim$ 0.3--0.5. Finally, we have shown that the composition of the post-shock material is able to match the bulk porosity and chondrule-to-matrix ratios of meteorite groups such as carbonaceous chondrites and unequilibrated ordinary chondrites.