The Dhajala meteorite shower: Atmospheric fragmentation and ablation based on cosmic ray track studies

Cosmic-ray track studies have been carried out in more than 250 fragments of Dhajala meteorite comprising greater than 70% of the recovered mass. In the case of larger fragments (namely, those with mass exceeding 250g) several faces of each fragment have been analysed for track densities. Track densities are low, and fall generally in the range (10³-10⁵)cm^-2, indicating appreciable ablation losses since the cosmic ray exposure age of Dhajala is about 7 m.y. (track measurements were confined to large olivine grains to minimize contributions to tracks due to the fission of uranium and extinct radionuclides). Attempts have been made to deduce information about fragmentation dynamics and the preatmospheric mass/radius of Dhajala, based on the present comprehensive study of track densities in the fragments. Correlations between the position of a fragment in the strewnfield and its track density have provided us with an approximate scenario for the fragmentation/ablation of the meteorite during its atmospheric flight. Observation of minimum track density in the fragments lead to a value of (38±2) cm for the preatmospheric radius of the meteorite. It is estimated from these data that the collection of fragments was made with an overall efficiency of ≈60% and that the ablation amounts to (86.7±2.1)%. Estimated amounts of ablation for shells of different radii are also presented.