Abstract DGP2026-82

Microscopic extra-terrestrial iron-rich spherules found on Earth can be classified into two categories: 1) cosmic spherules (a.k.a. micrometeorites) that originate from individual iron-rich cosmic dust grains melting during atmospheric entry; and 2) ablation spherules that separate from large iron impactors through melting and separation or evaporation and condensation during atmospheric passage. As both types of spherules originate from a similar parent material, they cannot be distinguished easily from each other through chemical or isotopic analysis. Their interaction with the atmosphere modifies their composition and mineralogy even more, further complicating the study of their parent material. Still, these spherules can be easily extracted from their host sediment due to their magnetic properties and are highly weathering resistant, creating an important alleyway into the iron-rich materials of our Solar System.  

We present preliminary results on iron-rich spherules retrieved from sediment samples collected during a field campaign in 2024 to the Heradura clay pan in the Atacama Desert, Chile. Two soil pits, 50 m apart, exhibit a greater content of spherical particles in samples taken 130 cm below the surface compared to any horizon above or below, with around two (2) spherules per gramm of sample material. Additionally, the amount of metal spherules in one of the pits far exceeds the typical fraction of 2% encountered in other collections with more than 75 % of all spherules here appearing metallic. Most metal particles are highly spherical and exhibit little variation in their diameter between 120 to 140 µm, however, some are up to 200 µm or even below 20 µm wide. Surface morphologies can differ greatly with some particles even exhibiting an agglomerated appearance. Many particles show caved-in surfaced and reveal an internal cavity surrounded only by a few µm-thick massive metallic shell. Qualitative elemental analysis shows Fe as their main component, with differing trace amounts of Al, Si, Ti, Cr and Mn. Ni has not been detected and whilst O is measurable on all exterior surfaces, some measurements of the interior shell show little to no O.  

Current results are inconclusive regarding whether the studied spherules stem from an extra-terrestrial source or could be related to anthropogenic contamination. However, the sediment layer at 130 cm depth, in which this excess of iron-rich spherules appears, has been dated to be around 12 to 13 ka. Although speculative, this age coincides with the Younger Dryas cooling episode of 12.9 to 11.7 ka and could therefore be related to the controversially discussed Younger Dryas Impact Event.