Iron Rain: measuring the occurrence rate and origin of small iron meteoroids at Earth

TL;DR

This four-year survey used EMCCD cameras to identify and analyze small iron meteoroids at Earth, revealing their abundance, orbital characteristics, and potential origins, especially at slow speeds and faint magnitudes.

Contribution

The study introduces a new physical property-based method to identify iron meteors and provides the first comprehensive characterization of their occurrence and orbital origins.

Findings

Iron meteors are most common at speeds below 15 km/s.

Approximately 20% of slow meteors are iron-rich.

Iron meteors have asteroidal, evolved orbits suggesting long collisional lifetimes.

Abstract

We report results of a four-year survey using Electron Multiplied Charged Coupled Device (EMCCD) cameras recording 34761 two-station video meteor events complete to a limiting magnitude of +6. The survey goal was to characterize probable iron meteoroids. Using only physical properties of the meteor trajectories including early peaking light curves, short luminous trajectories, and high energies accumulated per area at beginning, we identified 1068 iron meteors. Our iron candidates are most abundant at slow speeds < 15 km/s, where they make up approximately 20% of the mm-sized meteoroid population. They are overwhelmingly on asteroidal orbits, and have particularly low orbital eccentricities and smaller semi-major axes when compared to non-irons between 10-20 km/s. Our iron population appears to be more numerous at fainter magnitudes, comprising 15% of slow (10-15 km/s) meteors with peak brightness of +3 with the fraction rising to 25% at +6 to +7, our survey limit. The iron orbits are most consistent with an asteroidal source and are in highly evolved orbits, suggesting long collisional lifetimes (107 years). Metal-rich chondrules (nodules) found in abundance in EL Chondrites are one possible source for this population. We also propose a possible technique using R-band colours to more robustly identify fainter iron meteors with very high confidence.