Lunar surface exposure models for meteorites Elephant Moraine 96008 and Dar al Gani 262 from the Moon

Abstract— We derived the cosmic‐ray and solar particle exposure history for the two lunar meteorites Elephant Moraine (EET) 96008 and Dar al Gani (DaG) 262 on the basis of the noble gas isotopic abundances including the radionuclide ⁸¹Kr. For EET 96008, we propose a model for the exposure to cosmic rays and solar particles in three stages on the Moon: an early stage ～500 Ma ago, lasting less than 9 Ma at a shallow shielding depth of 20 g/cm², followed by a stage when the material was buried, without exposure, until it was exposed in a recent stage. This recent stage, at a shielding depth in a range of 200–600 g/cm², lasted for ～26 Ma until ejection. This model is essentially the same as that previously found for lunar meteorite EET 87521; thus, pairing of the two Elephant Moraine lunar meteorites that were recovered on the same icefield in Antarctica is confirmed by our data. The cosmic‐ray‐produced isotopes, the trapped solar and lunar atmospheric noble gases, as well as the radionuclide ⁸¹Kr observed for the DaG 262 lunar meteorite are consistent with a one‐stage lunar exposure history. The average burial depth of the Dar al Gani material before ejection was within a range of 50–80 g/cm². The exposure to cosmic rays at this depth lasted 500–1000 Ma. This long residence time for Dar al Gani at relatively shallow depth explains the high concentrations of implanted solar noble gases.