The earliest history of the moon remains poorly understood. The geological record of the first ~600 MYR of lunar evolution has been largely erased as a result of the heavy bombardment of the moon,…

The National Aeronautics and Space Administration (NASA) awarded a $209,472.05 grant to the University of Arizona, doing business as the Arizona Board of Regents, to investigate density anomalies in the lunar subsurface using data from the Gravity Recovery and Interior Laboratory (GRAIL) mission. The work aims to provide insights into the early geologic evolution of the Moon, which has been largely obscured by heavy bombardment and volcanic resurfacing. The grant supports research to leverage GRAIL gravity data in analyzing small-scale and large-scale density variations within the lunar crust that could reveal signatures of ancient internal processes. This grant does not have a set-aside designation.

The earliest history of the moon remains poorly understood. The geological record of the first ~600 MYR of lunar evolution has been largely erased as a result of the heavy bombardment of the moon, which has destroyed virtually all surface record of pre-nectarian processes aside from a few of the largest impact basins formed during that time [wilhelms, 1987]. On the nearside of the moon, the early geologic record has been further obfuscated by the extensive resurfacing by the maria. However, this early period would have been characterized by a high heat flux and enhanced rate of internally driven geodynamic, volcanic, and tectonic activity, and thus is a critical chapter in the evolution of the moon. Fortunately, a subsurface record of the early evolution of the moon may persist, and can be probed with the use of gravity data. Gravity data is useful for studying any process that leaves a signature in the distribution of density in the subsurface. Ancient intrusive activity may have generated discrete zones of increased density within the crust, variations in heat flow may have affected crustal porosity, tectonic and impact processes may have uplifted the crust-mantle interface, and volcanic processes may have buried the ancient topography resulting in variations in the thickness of the volcanic fill. Interpretations of low-resolution pre-grail gravity datasets have been largely limited to simple assumptions of variations in the thickness and isostatic state of a uniform density crust overlying a uniform density mantle [e.g., neumann ET AL., 1996; wieczorek and phillips, 1998; 1999; andrews-hanna, 2013]. Grail observations have shown these assumptions to be incorrect at all scales. Large-scale variations in crustal density have been mapped out using the correlation between the gravity and the topography [wieczorek ET AL., 2013]. At the same time, smallscale gravity anomalies cannot arise from crustal thickness variations because of the extreme attenuation of short wavelength anomalies as they are propagated from the crust-mantle interface to the surface, and therefore these anomalies must reflect small-scale shallow density variations within the crust. The proposed work will use grail gravity data to investigate density anomalies within the lunar crust at a range of scales and in a variety of geodynamic settings.