The impact and recovery of asteroid 2018 LA

The June 2, 2018, impact of asteroid 2018 LA over Botswana is only the second asteroid detected in space prior to impacting over land. Here, we report on the successful recovery of meteorites. Additional astrometric data refine the approach orbit and define the spin period and shape of the asteroid. Video observations of the fireball constrain the asteroid’s position in its orbit and were used to triangulate the location of the fireball’s main flare over the Central Kalahari Game Reserve. 23 meteorites were recovered. A consortium study of eight of these classifies Motopi Pan as a HED polymict breccia derived from howardite, cumulate and basaltic eucrite, and diogenite lithologies. Before impact, 2018 LA was a solid rock of about 156 cm diameter with high bulk density about 2.85 g/cm3, a relatively low albedo pV about 0.25, no significant opposition effect on the asteroid brightness, and an impact kinetic energy of about 0.2 kt. The orbit of 2018 LA is consistent with an origin at Vesta (or its Vestoids) and delivery into an Earth-impacting orbit via the nu_6 resonance. The impact that ejected 2018 LA in an orbit towards Earth occurred 22.8 +/- 3.8 Ma ago. Zircons record a concordant U-Pb age of 4563 +/- 11 Ma and a consistent 207Pb/206Pb age of 4563 +/- 6 Ma. A much younger Pb-Pb phosphate resetting age of 4234 +/- 41 Ma was found. From this impact chronology, we discuss what is the possible source crater of Motopi Pan and the age of Vesta’s Veneneia impact basin.

💡 Research Summary

The paper presents a comprehensive study of asteroid 2018 LA, the second object ever detected in space before impacting land, and the successful recovery and analysis of its meteorite fragments, named Motopi Pan. The authors combine new astrometric observations, video fireball recordings, and orbital dynamics to refine the pre‑impact trajectory, determine the spin period (~8.5 s) and an elongated shape (≈1.6 m × 1.2 m), and locate the main flare of the fireball over Botswana’s Central Kalahari Game Reserve at roughly 30 km altitude.

Field searches began 21 days after the event, yielding the first 17.92‑g stone (MP‑01). A coordinated effort in October recovered an additional 22 pieces, bringing the total to 23 recovered meteorites. Eight representative samples were subjected to an extensive suite of analyses: high‑resolution X‑ray micro‑CT and 3‑D laser scanning for internal structure, magnetic susceptibility, bulk and grain density, X‑ray fluorescence, and reflectance spectroscopy. The bulk density (≈3.12 g cm⁻³) and albedo (pV≈0.25) indicate a solid, relatively dense body with a kinetic impact energy of ~0.2 kt.

Petrographic work (BSEM, EMPA) shows that the recovered stones are a polymict breccia containing diogenite, eucrite, and howardite lithologies. Mineral chemistry confirms typical HED signatures: high‑Mg pyroxenes in diogenite fragments, Ca‑rich pyroxenes in eucrite pieces, and a mixture of both in howardite material. Spectral measurements reproduce the characteristic 1‑µm and 2‑µm absorption bands of Vesta‑derived material.

Isotopic investigations provide the chronological framework. Zircon U‑Pb ages (4563 ± 11 Ma) and concordant 207Pb/206Pb ages (4563 ± 6 Ma) record the formation age of the parent body, identical to Vesta’s accretion age. A younger Pb‑Pb resetting age in phosphates (4234 ± 41 Ma) records a later thermal event, possibly related to impact heating. Chromium isotopes (ε⁵³Cr) match Vesta’s signature, reinforcing the provenance. Cosmic‑ray exposure (CRE) ages of ~22 ± 2 Ma indicate that the meteoroid was liberated from Vesta roughly 22 million years ago, a timescale consistent with the formation age of the Veneneia (and possibly Antonia) impact basin on Vesta.

Dynamical modeling shows that the meteoroid’s orbit evolved via the ν₆ secular resonance, delivering it directly from the Vesta–Vestoid region into an Earth‑crossing trajectory without requiring an intermediate Vestoid parent. This pathway explains the observed orbital elements and the relatively low entry speed.

The authors discuss the implications of these findings for the source crater on Vesta. The age alignment, combined with the polymict nature of Motopi Pan, points to a large, deep‑seated impact (most plausibly the Veneneia basin, ~23 Ma old) as the origin of the fragment. The study demonstrates that pre‑impact detection, rapid ground‑based fireball triangulation, and coordinated meteorite recovery can yield a complete chain from space‑based observation to laboratory analysis, providing a rare “ground‑truth” for Near‑Earth Object (NEO) studies.

In conclusion, 2018 LA and its recovered meteorites constitute a valuable data set linking a specific NEO to a well‑characterized parent body, offering insights into delivery mechanisms, impact chronology, and the physical properties of small Earth‑impacting asteroids. The work underscores the importance of integrated observation‑recovery networks for planetary defense and for advancing our understanding of solar‑system material transport.