The atmospheric entry of micrometeorites on Mars: Implications for their mineralogy, texture and organic constituents

Abstract

The nature of martian micrometeorites (MMs) was investigated in this thesis through micro-analysis of terrestrial MMs and computational and experimental simulations of atmospheric entry heating. The biases in the Larkman Nunatak micrometeorite collection revealed in this study (Chapter 3) are attributed to the strong winnowing effects associated with sediment transport by aeolian processes. The weathering features observed in these micrometeorites are related to interaction with transient water. Sediment transport on Mars is dominated by aeolian processes, thus accumulations are likely to be similar to wind driven collections on Earth. However, their weathering state is expected to differ from terrestrial micrometeorites owing to the lack of water and much longer accumulation periods and is instead thought to be dominated by perchlorate induced oxidation. Computational simulations of atmospheric entry (Chapter 4) suggest much greater quantities of large, low temperature micrometeorites reaching the martian surface. The lower temperatures and larger particles surviving on Mars are likely to aid in the preservation of micrometeorite derived organic material with large portions of the micrometeorite flux expected to remain below the sublimation temperature of some organic compounds and larger particles allowing thermal gradients to form within particles. Experimental simulations (Chapter 5) indicate several differences between terrestrial and martian particles. Iron oxide phases were lacking in the martian particles including a magnetite rim, which is observed in the severely heated terrestrial particles. Additionally, sulphur and phosphorus are preserved in much greater quantities and in reduced forms in the martian particles. Raman spectroscopy also revealed that micrometeorite derived organic material on Earth experience greater evolution through the expansion of sp2 cluster diameter and growth of aromatic ring structures. Most of these features can be attributed to oxidative processes. Thus, atmospheric composition is thought to be a controlling factor in the nature micrometeorite derived organic material reaching a planetary surface.