Reconstructing the history of the Galaxy through the study of lunar samples
Louise Alexander
Birkbeck, University of London
Ian A. Crawford (Birkbeck, University of London), James Schwanethal (UCL), Katherine H. Joy (University of Manchester), Pieter Vermeesch (UCL), and Natalie Curran (University of Manchester)
Since the formation of the Sun ~ 4.6 billion years ago, the Solar System has orbited the Galaxy approximately 20 times and been exposed to a wide range of galactic environments as it passes through the spiral arms and star-forming regions. Supernova explosions, and associated supernova remnants will result in an enhanced galactic cosmic ray (GCR) flux which may be recorded in the lunar geological record [1, 2]. Measuring concentrations of cosmogenic isotopes (3He, 21Ne and 38Ar) in lunar samples of known ages may help to examine variations in the GCR flux over time. There are limitations in that the existing samples collected from the present surface regolith, have unknown shielding histories, and are not ideal for studies of this kind. However, the study of cosmogenic isotopes in lunar samples illustrates the potential to obtain information not only about the Moon and the cosmic ray exposure history of the lunar regolith, but also about the Earth, the early Solar System and the Galaxy. Accessing appropriate samples in future lunar missions will require advanced drilling and sample return capabilities in order to access the sub-surface and return a diverse range of samples to Earth for analysis. This would be facilitated by the presence of human explorers on the lunar surface.

References: [1] Crawford, I.A. et al. (2010) Earth, Moon and Planets, 107, 75-85. [2] Crawford and Joy (2014) Phil. Trans. R. Soc. A 372.