Minimoon still on the loose

TL;DR

This study reports the recovery of a meteorite linked to a fireball event in South Australia, but evidence suggests it is not the same object, highlighting challenges in confirming fireball-meteorite associations.

Contribution

The paper presents a detailed analysis of a meteorite recovered near a fireball event, demonstrating the importance of verifying fireball-meteorite pairings to avoid misidentification.

Findings

Meteorite was found 3.2 kyr after fall, not linked to 2016 fireball.

Contamination probability from other falls is less than 2%.

Fireball-meteorite pairing verification is crucial to avoid errors.

Abstract

On Aug 22, 2016, a bright fireball was observed by the Desert Fireball Network in South Australia. Its pre-atmosphere orbit suggests it was temporarily captured by the Earth-Moon system before impact. A search was conducted two years after the fall, and a meteorite was found after 6 days of searching. The meteorite appeared relatively fresh, had a mass consistent with fireball observation predictions, and was at the predicted location within uncertainties. However, the meteorite did show some weathering and lacked short-lived radionuclides ($^{58}$Co, $^{54}$Mn). A terrestrial age based on cosmogenic $^{14}$C dating was determined; the meteorite has been on the Earth's surface for $3.2\pm1.3$ kyr, ruling out it being connected to the 2016 fireball. Using an upper limit on the pleistieocene terrain age and the total searched area, we find that the contamination probability from another fall is $<2\%$. Thus, the retrieval of the "wrong" meteorite is at odds with the contamination statistics. This is a key example to show that fireball-meteorite pairings should be carefully verified.