Investigation for Micrometeorites in Urban Environments

Micrometeorites (MMs) are extraterrestrial particles with a size between 30 and 1000 micrometers. These particles can be found on the Earths surface, as around 5,200 metric tons of MMs fall every year[1], corresponding to approximately 1x10-5 g m-2yr-1. Micrometeorites are often fragments of a larger object, and have specific compositions that correspond to the meteor, comet, or planetary body they are from. They provide scientists insight into near and distant celestial bodies and the processes that occur there. In this project, samples were collected from various locations in Rapid City, South Dakota, by sweeping the debris off roofs and collecting particles in the water from downspouts. Perhaps the single most challenging aspect of searching for MMs is distinguishing them from copious Earthly contamination. A powerful magnet was used to separate the magnetic particles from the rest of the debris, since a significant fraction of MMs are ferric. The samples of magnetic particles were spread onto slides and analyzed with an optical microscope to find particles with the distinctive morphology of MMs. A spherical shape and evidence of melting/crystallization along with a metal core are considered characteristics of MMs. We plan to do conduct further analysis to deduce the chemical and isotopic composition and confirm the identity of these MMs. [1] J. Rojas, et al., The micrometeorite flux at Dome C (Antarctica), monitoring the accretion of extraterrestrial dust on Earth, Earth and Planetary Science Letters, Volume 560, 2021.