K. Nishiizumi¹, M. W. Caffee², Y. Hamajima³, R. C. Reedy⁴ and K. C. Welten¹

¹Space Sciences Laboratory, University of California, Berkeley, California, USA
²Department of Physics, Purdue University, West Lafayette, Indiana, USA
³Low Level Radioactivity Laboratory, Kanazawa University, Nomi, Ishikawa, Japan
⁴Planetary Science Institute, Los Alamos, New Mexico, USA

The Sutter’s Mill (SM) carbonaceous chondrite fell in California on April 22, 2012. The cosmogenic radionuclide data indicate that Sutter’s Mill was exposed to cosmic rays for 0.082 ± 0.008 Myr, which is one of the shortest ages for C chondrites, but overlaps with a small cluster at approximately 0.1 Myr. The age is significantly longer than proposed ages that were obtained from cosmogenic noble gas concentrations, which have large uncertainties due to trapped noble gas corrections. The presence of neutron-capture ⁶⁰Co and ³⁶Cl in SM indicates a minimum preatmospheric radius of approximately 50 cm, and is consistent with a radius of 1–2 m, as derived from the fireball observations. Although a large preatmospheric size was proposed, one fragment (SM18) contains solar cosmic ray–produced short-lived radionuclides, such as ⁵⁶Co and ⁵¹Cr. This implies that this specimen was less than 2 cm from the preatmospheric surface of Sutter’s Mill. Although this conclusion seems surprising, it is consistent with the observation that the meteoroid fragmented high in the atmosphere. The presence of SCR-produced nuclides is consistent with the high SCR fluxes observed during the last few months before the meteorite’s fall, when its orbit was less than 1 AU from the Sun.

Reference
Nishiizumi K, Caffee MW, Hamajima Y, Reedy RC and Welten KC (in press) Exposure history of the Sutter’s Mill carbonaceous chondrite. Meteoritics & Planetary Science
[doi:10.1111/maps.12297]
Published by arrangement with John Wiley & Sons

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