Author name: Andrew J. Westphal

When cosmic dust particles were first identified almost 140 years ago, few would have predicted that much would ever be known about these miniscule objects, given the existing state of the art in analytical techniques. Times have changed. Today, in a single extraterrestrial dust particle, we can detect all the elements present, measure isotopic ratios, determine the exact crystalline structures of the minerals and the oxidation state of cations in those minerals, and even resolve individual atoms. The results are telling fascinating stories about the nature and histories of the particles that come to Earth. We review the most common techniques that help unravel these cosmic stories.

Many cosmic dust particles have escaped the aqueous and thermal processing, the gravitational compaction, and the impact shocks that often overprint the record, in most larger samples, of how Solar System materials formed. The least-altered types of cosmic dust can, therefore, act as probes into the conditions of the solar protoplanetary disk when the first solids formed. Analyses of these “primitive” particles indicate that the protoplanetary disk was well mixed, that it contained submicron grains formed in a diversity of environments, that these grains were aerodynamically transported prior to aggregation, which was likely aided by organic grain coatings, and that some minerals that condensed directly from the disk are not found in other materials. These protoplanetary aggregates are not represented in any type of meteorite or terrestrial rock. They can only be studied from cosmic dust.