INVESTIGATING THE EFFECTS OF ATMOSPHERIC ENTRY ON COSMIC DUST USING ATOM PROBE TOMOGRAPHY

Cosmic dust is a key ingredient in the formation of the Solar System and is the precursor to planetesimals that accrete into the planets we observe today. This material is predominantly derived from asteroidal and cometary bodies and, due to an inwardly spiralling trajectory, may intersect the Earth. Dust particles can be classified as micrometeorites (MMs), which are collected on the Earth’s surface, and interplanetary dust particles (IDPs), retrieved from the atmosphere. Cosmic dust undergoes thermal processing as it enters Earth’s atmosphere, and this processing will differ for MMs and IDPs due to differences in particle trajectories, sizes, shapes and compositions. Given the small size of cosmic dust (<1 mm), nanometre (nm)-scale analyses may reveal the geochemical consequences of atmospheric entry heating and enable constraints to be placed on associated models.

Here, we perform atom probe tomography (APT) analyses on two target regions within an Antarctic-recovered MM using site-specific sample preparation, to obtain 3D compositional maps at the nanoscale. Compositional and textural boundaries observed in back-scattered electron (BSE) and secondary electron (SE) images were acquired using an electron probe microanalyser (EPMA) at the Alabama Analytical Research Center (AARC), University of Alabama (UA). Focused ion beam (FIB) and APT techniques were employed at the University of Oxford. First, FIB was used to prepare two lamellae, from which APT needles were milled. Needle A from lamella R5111, divided into top (A1) and bottom (A2) tips, was run on a LEAP-5000XS and needles B and C from lamella R5083 were run on a LEAP-5000XR. The data was processed to yield 3D tip reconstructions. We have demonstrated the successful application of APT to cosmic dust – believed to be the first APT experiments on such material. The results reveal nm-scale heterogeneities, with elemental lineations, predominantly in iron and zinc, and species clustering, including a possible chromite inclusion, observed in needle A. Needle B shows a sharp compositional boundary, partitioning species such as carbon, magnesium and titanium from iron oxides. Future work will obtain APT data for other cosmic dust particles, allowing a comparison of the features observed in this MM that may be the consequence of atmospheric entry heating.