Moon United: Determining the Cosmic-Ray Exposure Ages of Pristine Lunar Samples.

Abstract:

Over the last ~4.5 Gyr, particles from the solar wind, the lunar interior, and the wider environment (e.g., solar cosmic rays, galactic cosmic rays, micrometeorites) have directly interacted with and/or been implanted into regolith exposed at the lunar surface. During this time, volatiles and organic compounds have also been added to the lunar regolith as a result of these interactions. For example, volatiles and organic molecules are delivered to the Moon by impacts, and may be produced and/or degraded during the interaction of the solar wind and cosmic rays with surface exposed regolith. Therefore, the regolith provides a unique archive of the processes that have affected the surface of the Moon through time.

The Moon United team (as part of the Apollo Next Generation Sample Analysis (ANGSA) consortium) will analyze a variety of particles (impact-melts, basalts and regolith breccias) and bulk soils from several regolith samples collected during the Apollo 17 mission, including two shadowed soils (72320 and 76240) and a double-drive tube (73001/2). These samples provide the opportunity to assess the input budget from the solar wind and exogenous sources, understand exposure histories with depth, and explore how the local region has evolved over time. The petrology (scanning electron microscope), mineral and bulk rock chemistry (electron microprobe), and noble gas budget (mass spectrometry) will be measured for each particle and soil sample. These data will be used to determine parent lithology and constrain the regolith history (e.g., cosmic ray exposure age, maturity, gardening history) of the samples and provide crucial context to the exposure history experienced by volatile and organic compounds within them. These measurements will offer significant value to the ANGSA consortium efforts to understand the complete geologic history of the samples, the Apollo 17 landing site, and lunar processes.