Fireball flickering: the case for indirect measurement of meteoroid rotation rates

Data collected during the Meteorite Observation and Recovery Program (MORP) indicate that 4% of bright fireballs show a periodic variation or flickeri ng in brightness. The observed flickering frequencies vary from a few Hz to as high as 500 Hz. We interpret the Bickering phenomenon in terms of meteo roid rotation. The MORP data does not reveal any apparent correlation betwe en the flickering frequency and the properties of the meteoroid or the atmo spheric flow conditions under which ablation is taking place. It is argued that the most likely cause of the flickering phenomenon is the rotational m odulation of the cross-section area presented by the meteoroid to the on-co ming ah-how. A study is made of the Peekskill fireball and it is concluded that the meteoroid was spun-up during its long flight through the Earth's a tmosphere, and that its initial brake up was due to rotational bursting. We also argue that the Peekskill event provides the best observational eviden ce that the flickering phenomenon is truly related to the rotation rate of the impinging meteoroid. We find that the observed rotation rates of the MO RP fireballs are clustered just below the allowed limit set by rotational b ursting, but argue that this is due to an observational selection effect th at mitigates against the detection of low-frequency flickering. (C) 2000 El sevier Science Ltd. All rights reserved.