Micrometeorite collections: a review and their current status.

Micrometeorites are estimated to represent the main part of the present flux of extraterrestrial matter found on the Earth's surface and provide valuable samples to probe the interplanetary medium. Here, we describe large and representative collections of micrometeorites currently available to the scientific community. These include Antarctic collections from surface ice and snow, as well as glacial sediments from the eroded top of nunataks-summits outcropping from the icesheet-and moraines. Collections extracted from deep-sea sediments (DSS) produced a large number of micrometeorites, in particular, iron-rich cosmic spherules that are rarer in other collections. Collections from the old and stable surface of the Atacama Desert show that finding large numbers of micrometeorites is not restricted to polar regions or DSS. The advent of rooftop collections marks an important step into involving citizen science in the study of micrometeorites, as well as providing potential sampling locations over all latitudes to explore the modern flux. We explore their strengths of the collections to address specific scientific questions and their potential weaknesses. The future of micrometeorite research will involve the finding of large fossil micrometeorite collections and benefit from recent advances in sampling cosmic dust directly from the air. This article is part of the theme issue 'Dust in the Solar System and beyond'.

Quantitative estimation of elemental composition employing a synthetic generated spectrum.

Composition of multielement samples is estimated by using a synthetic generated spectrum utilizing a nonlinear fitting routine. By fitting simultaneously a large number of emission lines, the error in the estimation is minimized. The procedure for synthetic spectrum generation includes self-absorption of emission lines by taking into account the number density of different species in the plasma. The Stark width of different emission lines is iteratively calculated based on the observed width and the degree of self-absorption in the individual lines. This procedure is found to be successful for achieving convergence of the retrieval algorithm even for dense spectra as well as for resolving merged lines with accuracy. This scheme was applied on a stainless steel and brass sample, and the laser-induced breakdown spectroscopy results match well with the reference value obtained from the electron probe microanalyzer measurement.

Anthropogenic spherules in Zuari estuary, south west coast of India.

In this study we report silica rich anthropogenic spherules from the marine environment. We found spherical, dumbbell, teardrop and fused spherules in Zuari estuary (near the Dona paula jetty), south west coast of India. The spherules were composed of SiO2 (69.8%), Na2O (13.2%), CaO (8.8%), MgO (3.8%), and traces of Al2O3, and FeO. Their high Na and Ca contents rules out the possibility of being an impact spherule or microtektite, or anthropogenic spherules coming from fly ash. Their elemental composition suggests that these are glass micro beads that have many applications including production of road and pavement marking materials, such as traffic paints. Considering that the glass micro beads are known to have high concentrations of Pb, As, and Sb that can leach into the marine environment, this study also raises questions regarding the impact of such spherules on marine biota, and highlights the need for further detailed study.

Characterisation, Sources and Flux of Unmelted Micrometeorites on Earth During the Last ~50,000 Years.

Dust dominates extraterrestrial flux on the earth (30,000 tonnes/yr), however only ~5% of the cosmic dust survives atmospheric entry which is basically in two forms: melted and unmelted. Melted micrometeorites undergo transformational changes due to heating during atmospheric entry which obliterate evidences regarding their precursors. Unmelted micrometeorites (UMM) survive atmospheric entry with minimal alteration, they provide direct evidence for their parent bodies. Recent investigations unravelled a wide range of UMM, there are however no quantitative estimates of sources that contribute to the cosmic dust accreted by the Earth.