Analysis of Magnetization Directions of Lunar Swirls

Lunar Swirls are high albedo markings on the Moon that exist in the regions of some crustal magnetic anomalies. The precise mechanism responsible for the swirl features is unknown but a prevailing theory is solar wind standoff, where the magnetic field from subsurface magnetized sources protects the lunar surface from solar wind ions, leading to their lesser maturation and brighter appearance. If this theory is correct, the magnetic field of the anomalies should heavily influence the appearance of the swirl. To better understand the cause of swirls, the magnetization direction of the source creating the field is analyzed. This study uses differences of the vector fields measured along satellite orbits (20-40 km above the lunar surface), which have lesser noise because time-varying external fields in the lunar environment are nearly the same for short times between consecutive data points. The magnetization of the magnetic features is derived by best-fitting fields from a set of unidirectional magnetized dipoles. The best-fit is judged by comparing computed vector fields with the observed vector fields (their misfit) and their correlation coefficient. Magnetization directions of the magnetic features analyzed in the study do show a strong relationship between the magnetization directions and the appearance of the swirl. After obtaining the magnetization directions, the corresponding magnetic paleopoles were determined. The paleopole locations do not coincide with the current rotational axis of the Moon (assuming a dipolar core field) and are fairly spread out over the Moon. If the Moon did possess an early dipolar core dynamo then it was most likely not aligned with the present rotational axis. The uncertainty in the magnetization directions and derived paleopole locations as judged by best-fit magnetization directions using different criteria is fairly large