Constraining flight history of micrometeorites through porosity.

Abstract:

Studying how cosmic dust travel and arrive on Earth provides essential insights into the dynamical effects on dust in our Solar System. X-ray Computed Tomography (X-CT) is increasingly applied to analyze extra-terrestrial samples in the laboratory. Here we demonstrate how this non-destructive technique can resolve the dynamical effects undergone by micrometeoroids before and during their atmospheric flight. Micrometeorites (MMs) are originated from a more diverse population of small bodies as compared to macroscopic meteorites. This is due to differences in their delivery mechanisms. Here we focus on giant MMs, between 400 µm and 2 mm in diameter. They are more representative of their parent body lithology, and their larger size allows us to study the spatial distribution of their components.

In this study, we have examined the 3D morphological structure and petrofabric of 51 giants MMs collected by the PNRA (Programma Nazionale di Ricerca in Antartide) from a MM trap on the top of Miller Butte in the Transantarctic Mountains. We discuss their classification based on 3-D density contrast images, obtained by X-ray computed tomography. Analyses were performed during two campaigns of measurement on the PSICHE and ANATOMIX lines at the synchrotron SOLEIL (France) with a respective final pixel size of 0.6 µm and 0.325 µm.

We confirm the influence of the atmospheric entry on the global porosity (10–40 vol% for scoriaceous meteorites versus 0–25 vol% for unmelted particles). Thanks to their morphological properties and the spatial distribution of the pores we are able to infer the dynamical properties of their atmospheric flight history. For the first time, spinning entry is explicitly demonstrated for several partially melted MMs. Furthermore, we resolved the thermal gradient in a single particle observed as a progressive increase in pore abundance and size with higher peak temperatures.

Acknowledgment: PNRA16-00029 and PRIN2015-20158W4JZ7; ASI-INAF agreements I/032/05/0 and I/024/12/0; STFC grant no. ST/R000727/1. Measurements at SOLEIL were funded through proposal no. 20180438 and 20191248.