^1,2,3,4Sky P. Beard,^2,3Timothy D. Swindle,⁵Thomas J. Lapen,^2,3David A. Kring
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13927]
¹State Key Laboratory in Lunar and Planetary Science, Macau University of Science and Technology, Avenida Wai Long, Macau, Taipa, 999078 P.R. China
²NASA Solar System Exploration Research Virtual Institute, Moffett Field, California, 94035 USA
³Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, 85721 USA
⁴CNSA Macau Center for Space Exploration and Science, Macau, P.R. China
⁵University of Houston, Houston, Texas, 77004 USA
Published by arrangement with John Wiley & Sons

The LL5 chondrite Chelyabinsk has had numerous isotopic studies since its fall in 2013. These data have been used to suggest ~8 impact events recorded from multiple isotopic systems (e.g., Ar-Ar, U–Pb, Sm-Nd, Rb-Sr, among others). We report details of Ar-Ar and U-Pb results and re-evaluate the geochronology of Chelyabinsk. Argon has the youngest Ar-Ar age recorded in meteorites, 25 ± 11 Ma, and an older resetting event at ~2550 Ma. The U-Pb analysis has an upper concordia age of 4456 ± 23 Ma and a lower concordia age of 184 ± 200 Ma. The lower concordia intercept represents a later thermal event (e.g., an impact), the most recent time that lead loss occurred, and could represent resetting by the youngest event recorded by Ar-Ar. Combining our data with literature results, we find strong evidence of at least four impact events (~4450, 2550, 1700, 25 Ma), with some evidence for two additional impacts (~3700, 1000 Ma).

¹Lukáš Shrbený,²Agata M. Krzesińska,¹Jiří Borovička,¹Pavel Spurný,³Zbigniew Tymiński,⁴Kryspin Kmieciak
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13929]
¹Astronomical Institute of the Czech Academy of Sciences, Ondřejov, 251 65 Czech Republic
²Centre for Earth Evolution and Dynamics, Department of Geosciences, University of Oslo, Oslo, N-0371 Norway
³National Centre for Nuclear Research, POLATOM Radioisotope Centre, Otwock, 05-400 Poland
⁴Meteorite Finder
Published by arrangement with John Wiley & Sons

We present the description of an observation of a fireball recorded during the sunrise on July 15, 2021. Atmospheric trajectory, impact area, and heliocentric orbit were determined on the basis of three instrumental video records. The terminal part of the fireball was not instrumentally recorded due to clouds. Based on our computations, one meteorite was found in the predicted impact area by Polish searchers. The specimen was, soon after recovery, analyzed for the presence of short-lived radionuclides and the measurement confirms a very fresh fall, coinciding with the time of the fireball event. The recovered meteorite, Antonin, is an unbrecciated L5 chondrite with shock stage S3, weathering grade W0, and bulk density of 3.42 g cm−3. Unusual for L chondrites, it contains assemblages composed of metal and two sulfides, troilite and mackinawite. We interpret these assemblages to have been formed as products of shock metamorphism and post-shock annealing on the parent body. This suggests that the thermal and collisional history of the Antonin parent body was complex.