To catch a falling star

This study set out to provide insights into the composition and characteristics of the recent cosmic dust flux accreted to Earth and to underscore the potential and importance of rooftop micrometeorites. The thesis has taken on an interdisciplinary nature, integrating petrological, mineralogical, geochemical, cosmochemical, and isotopic examination, intended to advance our understanding of the chemical diversity and evolution of the Solar System. Through the development of improved separation methods, several micrometeorite collections, containing primarily cosmic spherules (CSs), have been established from various environments and geographical locations, including the Netherlands (Chapter 2), Antarctica and Chile (Chapter 4), and Gran Canaria (Chapter 6). Ancillary results presented in Chapter 5 include a large collection of impact particles from an airburst touchdown event at the Antarctic site. The oxygen isotopic analyses of young rooftop micrometeorites from the Netherlands, discussed in Chapter 3, have given us a fresh look into the composition of the modern-day flux of cosmic dust accreted to Earth. The findings are consistent with previous reports on older micrometeorites, indicating no major changes in the flux during the past few million years. In addition, it was found that up to ~15% of CSs originate from a parent body that experienced pronounced aqueous alteration by isotopically heavy water. Recent work presented in Chapter 7 indicates a link to near-Earth CY chondrite asteroids, which is currently being further explored. In Chapter 4, a comparative study of the three largest established CS collections, originating from a hot desert, a cold desert, and a rooftop in a temperate climate, has shown that once operator bias-induced differences introduced during the separation and classification processes are negated, the collections show consistent population statistics, assumed to approximate the recent time-averaged flux. Further insights regarding the change of relative CS abundances with size enable the reconciliation of conflicting literature reports. Aligning with the conclusions from Chapter 3, the results indicate that the cosmic dust flux has remained rather stable in terms of mass, type, and size distribution during the past few million years. In addition, it has been shown that the flux is composed of multiple sources, of which some minor sources could have slightly varied in relative contribution through time. Finally, a pilot study on Gran Canaria discussed in Chapter 6 has further demonstrated the simplicity with which rooftop micrometeorites can be collected and their potential for future analyses, discoveries, and citizen scientist collaborations. Collectively, this work provides a solid foundation for further developments of collection and separation techniques and refines our understanding of the cosmic dust flux accreted on Earth. By situating these findings within the broader context of planetary sciences, this thesis emphasizes the value of micrometeorites to study large-scale processes in the Solar System. As new and more precise analytical techniques and an increasing number of micrometeorites become available, cosmic dust could play an important role in answering some of the major questions within the fields of Earth sciences, biology, and cosmology.