micrometeorites

Micrometeorites are tiny extraterrestrial particles that reach Earth after being shed from comets, asteroids, or interplanetary dust. They are generally defined as particles smaller than about a couple of millimeters in diameter, with most samples ranging from tens of micrometers up to a few hundred micrometers. Through atmospheric entry, many micrometeorites experience melting and rapid cooling, producing glassy spheres known as cosmic spherules; others survive with unmelted or partially melted textures that preserve primitive components.

Most collections come from regions where terrestrial contamination is minimal, notably Antarctic and Greenland ice, where micrometeorites concentrate as snow and ice accumulate, and from certain deep-sea sediments. Recovery involves processing large volumes of ice or sediment, removing terrestrial material, and identifying extraterrestrial particles using microscopy and isotopic analyses. Researchers distinguish micrometeorites from terrestrial dust and from larger meteorites by their mineralogy, textures, and noble-gas signatures, among other indicators.

Composition and textures of micrometeorites are diverse. They include silicate-dominated particles with glassy matrices containing olivine, pyroxene, and other minerals, as well as metallic iron-nickel grains and rare sulfides. Some samples are highly altered by terrestrial weathering, but many preserve characteristics that reflect their solar-system origins. Iron- and nickel-rich micrometeorites and cosmic spherules often exhibit features formed during atmospheric melting, while unmelted micrometeorites retain primitive, chondritic textures similar to early solar system material.

Micrometeorites provide direct, small-scale samples of solar-system material, complementing meteorites and IDPs. They yield information on the composition of the early solar system, the flux of interplanetary dust, and processes such as solar wind implantation and cosmic-ray exposure, contributing to studies of planetary formation and the history of space weathering.