Abstract
The origin and evolution of the Moon's magnetic field has been a major question in lunar science ever since Luna 1 made the first magnetic measurements in the vicinity of the Moon in 1959. Orbital measurements show that the magnetic field at the surface of the Moon has local scale lengths on the order of 1-100 km. While this could suggest a correlation with impact craters, most lunar magnetic anomalies don’t appear to correlate with known geologic structures, including impacts [1]. However, the magnetic field produced by impact events are spatially and temporally complex. Add in the complexity of remanence acquisition (localized regions of heating/cooling and/or shock that can produce remanence in the presence of a magnetic field) and we have the potential for a complex pattern to emerge. Wieczorek et al. [1] showed just how such complexity may play out. In their simulations, some lunar magnetic anomalies may be caused by regions of concentrated magnetic materials associated with fragments of the South Pole-Aitken impactor, especially if the impactor was differentiated with an iron core. More recently, Oliveira et al. [2] showed that magnetic anomalies associated with five large lunar basins may be caused by impact melt sheets that cooled in the presence of an early lunar dynamo. In this paper we will look at an alternative explanation for many lunar anomalies that doesn’t require the presence of a lunar dynamo. At least some lunar anomalies may be associated with a deeper, thicker yet more varied region of magnetization acquired by rocks that became hot and cooled rapidly enough during crater formation to have acquired the transient magnetic field produced by the impact itself.
