Evidence for Deposition of Interstellar Material on the Lunar Surface

Astronomical observations indicate that one or more supernovae (SN) ocurred in the vicinity of our solar system in the recent past (~10Myr) [1,2]. One possible indication of the arrival of SN (or perhaps AGB) debris locally was the detection of 60Fe/Fe (T1/2 = 2.62 Myr [3]) excesses in a ferroman-ganese crust from the Pacific Ocean [4,5]. Another indication came from the Moon. In a previous study [6] we reported a 60Fe/Fe depth profile constructed with 2 samples of the Apollo 12 core 12025, 4 samples of the Apollo 15 core 15008, 2 samples known as ‘skim’, ‘scoop’ and ‘under boulder’ soil collected near the shade of a small boulder in Station 9 during the Apollo 16 mission (shaded samples), and 5 samples of the deep drill core 60007/6, sampled during the same mission. We complete the previous work by reporting new measurements of 53Mn (T1/2 = 3.7 Myr [7]) in the same samples, including deeper samples of the 12025 core, and by using those measurements for a critical assessment of the 60Fe results. We also determined the activities of 60Fe and 53Mn of 7 samples from 4 iron meteorites; these activities were used to establish reference levels for local production due to galactic cosmic rays.