Analysis of a "flickering" Geminid fireball

Abstract

In the early morning hours of December 13, 2002, a bright Geminid fireball with an absolute magnitude of -9.2 ± 0.5 was observed from Southern Saskatchewan, Canada. The fireball displayed distinct small-scale oscillations in brightness, or flickering, indicative of the parent meteoroid being both non-spherical and rotating. Using the light curve derived from a calibrated radiometer, we determine a photometric mass of 0.429 ±  0.15 kg for the meteoroid, and we estimate from its initial rotation rate of some 6 Hz that the meteoroid was ejected from the parent body (3200) Phaethon some 2500 ± 500 years ago. We find that 70% of Geminid fireballs brighter than magnitude -3 display distinct flickering effects, a value that is in stark contrast to the 18% flickering rate exhibited by sporadic fireballs. The high coincidence of flickering and the deep atmospheric penetration of Geminid fireballs are suggestive of Geminid meteoroids having a highly resilient structure, a consequence, we suggest, of their having suffered a high degree of thermal processing. The possibility of Gemind material surviving atmospheric ablation and being sampled is briefly discussed, but the likelihood of collecting and identifying any such material is admittedly very small.