Source Parameter Interpretation of High Resolution Lunar Magnetic Anomalies from SELENE (Kaguya) and Lunar Prospector Data

Using a novel theoretical orbital data cross-validation method implemented by us last year in the region of South Pole - Aitken (SP-A) basin (Newman and Ravat, 2015, LPSC), this study will isolate nearly noise-free internal magnetic anomaly field components from SELENE/Kaguya and Lunar Prospector satellite orbits globally and generate a high quality, high resolution global as well as localized magnetic anomaly databases for geologic interpretation of the anomalies. The fields will be utilized in geophysical analysis and interpretation to determine edges and depths of strong magnetic sources on the Moon. These source parameters will allow us to constrain depths, depth extent, edges, and geometry of sources of magnetic anomalies in the SP-A basin and also other high amplitude and key anomaly regions on the Moon. This will in turn constrain the nature and importance of impact vs magmatic processes on the Moon during the time period when the core field dynamo was active. Magnetic fields from the Lunar Prospector (LP) and SELENE/Kaguya missions show strong anomalies in and around the South Pole-Aitken (SP-A) basin and near some of the major impact craters and enigmatic swirl regions. In the SP-A basin, previous researchers have hypothesized causes of strong lunar magnetic anomalies ranging from antipodal focusing of melt cloud from large impacts in surficial layers (Hood et al., several papers from 1979 to 2014), and specifically for the SP-A basin, highly magnetic impactor ejecta in surficial layers (Wieczorek et al., 2012, Science) to crustal magnetization of dike-like sources (Purucker et al., 2012, JGR). Sources of other major magnetic anomalies near impact craters and swirls are also debated and their nature would be elucidated by the techniques we will use in this study. With the high quality low-altitude global field component datasets from this study, we will determine source edges and depths and the origin of the enigmatic magnetic features in the SP-A basin and also in other regions of high amplitude magnetic features. Since gravity gradients and magnetic fields can be related when their sources have common geometrical attributes, where appropriate, we will also incorporate high spherical harmonic degree gravity anomaly models from GRAIL available at the PDS in our modeling and interpretation to understand further the nature of these sources. The results of this project will allow us to better understand the internal lunar structure and the dominant processes that formed it. We will use a number of direct geophysical interpretational techniques for determining source edges, geometry, and thickness (e.g., in the books by Blakely, 1995; Hinze et al., 2013; and Ravat et al. from 1996 to 2014: namely, spherical Euler deconvolution, spherical Total Gradient and Analytic Signal, and spectral layer top and bottom determination techniques from magnetic and gravity anomalies). Our present spectral magnetic depth determination results in the SP-A region (Newman and Ravat, 2015) show that the magnetic layer lies entirely inside the crust and is correlated with crustal thickness estimates from gravity (i.e., thin near the center of the SP-A basin and thicker on the margins). These results are already able to distinguish between the surficial highly magnetic impact ejecta interpretation and the dike injection model with magnetic sources extending to greater depths. However, more work remains to be done with the spherical Euler deconvolution method and the spherical Total Gradient and Analytic Signal methods to provide corroborating evidence. This is one aspect of the proposed investigation. All these methods, including the spectral depth determination, would also be helpful in understanding the origin of other high amplitude magnetic anomaly features on the Moon in conjunction with gravity and geologic data.