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

Abstract

We report results of a 4-yr survey using Electron Multiplied Charged Coupled Device cameras recording 34 761 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-1, where they make up ≈20 per cent of the mm-sized meteoroid population. They are overwhelmingly on asteroidal orbits, and have particularly low orbital eccentricities and smaller semimajor axes when compared to non-irons between 10 and 20 km s-1. Our iron population appears to be more numerous at fainter magnitudes, comprising 15 per cent of slow (10-15 km s-1) meteors with peak brightness of +3 with the fraction rising to 25 per cent 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 yr). 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.