The unexpected 2012 draconid meteor storm

Abstract

An unexpected intense outburst of the Draconid meteor shower was detected by the Canadian Meteor Orbit Radar on 2012 October 8. The peak flux occurred at ̃16:40 UT on October 8 with a maximum of 2.4 ± 0.3 h-1 km-2 (appropriate to meteoroid mass larger than 10-77 kg), equivalent to a ZHRmax ̃ 9000 ± 1000 using 5-min intervals, using a mass distribution index of s = 1.88 ± 0.01 as determined from the amplitude distribution of underdense Draconid echoes. This makes the outburst among the strongest Draconid returns since 1946 and the highest flux shower since the 1966 Leonid meteor storm, assuming that a constant power-law distribution holds from radar to visual meteoroid sizes. The weighted mean geocentric radiant in the time interval of 15-19 h UT, 2012 October 8, was αg = 262° 4 ± 0° 1, dg = 55° 7 ± 0° 1 (epoch J2000.0). Visual observers also reported increased activity around the peak time, but with a much lower rate (ZHR ̃ 200), suggesting that the magnitude-cumulative number relationship is not a simple power law. Ablation modelling of the observed meteors as a population does not yield a unique solution for the grain size and distribution of Draconid meteoroids, but is consistent with a typical Draconid meteoroid of mtotal between 10-6 and 10-4 kg being composed of 10-100 grains. Dynamical simulations indicate that the outburst was caused by dust particles released during the 1966 perihelion passage of the parent comet, 21P/Giacobini-Zinner, although there are discrepancies between the modelled and observed timing of the encounter, presumably caused by approaches of the comet to Jupiter during 1966-1972. Based on the results of our dynamical simulation, we predict possible increased activity of the Draconid meteor shower in 2018, 2019, 2021 and 2025. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.