On the spatiotemporal coincidence of meteorites in recent fall search campaigns

ABSTRACT The meteoritical community widely assumes that the probability of finding two meteorites from different falls laying in close proximity is negligible. However, recent studies have suggested that spatiotemporal coincidences may be critical when associating a meteorite with a witnessed fall. In this work, we estimate the number of accumulated meteorites – those resulting from past falls – that are present in landing regions of new falls, while accounting for the effects of terrestrial weathering. We present a simple, fast-computing model to estimate such probability, validated with a Monte Carlo approach based on dark flight computations from real meteorite-dropping fireball data. Considering meteorite masses higher than 10 g, our results indicate that in regions with minimal weathering, like Antarctica, the probability of encountering a previous meteorite within a new fall strewn field may be as high as 75 per cent. In environments with higher weathering rates, like countryside or urban regions, this probability decreases to $\lesssim 1~{{\ \rm per\ cent}}$. When considering the 30 g Lake Frome 006 meteorite coincidence case, the probability of recovering a non-related meteorite with an age of 3.2 kyr from a 0.7 km$^2$ search area is 6.9 per cent. In the case of the 1 kg Ischgl meteorite, the probability of coincidence with another fresh meteorite of similar mass is 0.06 per cent assuming a large strewn field of 210 km$^2$. Applied to the Almahata Sitta case, our model predicts a 11.3 per cent of coincidence with a previous meteorite fall. Our results strongly suggest that isotopic dating is essential before associating any meteorite with a witnessed fall.