Volcanic Activity at Von Kármán Crater: Identifying Three Distinct Basaltic Phases Using Lunar Penetrating Radar

Chang’E‐4 and its rover Yutu‐2 are the first artificial objects that soft‐landed on the far side of the Moon. Yutu‐2 is also the second planetary rover equipped with a set of ground‐penetrating radar (GPR) systems; two with 500 MHz (Channel‐2A&2B), and one with 60 MHz (Channel‐1) central frequency. GPR is a near surface geophysical technique capable of mapping the subsurface's dielectric properties, which are subsequently used to infer the mechanical and mineralogical properties of the lunar subsurface. The electromagnetic losses of lunar materials are primarily based on oxides of iron and titanium, and in particular on ilmenite. Ilmenite is abundant in Mare soils (%) and basalts (%). It is a unique mineral, being one of the few minerals with frequency dependent dielectric properties. Due to its dispersive nature, ilmenite is acting as a low‐pass filter, reducing the central frequency of an incident field. Experimental evidence suggests that the shift of the central frequency is proportional to the ilmenite content of the material. Consequently, frequency attributes of the received radar signal can be used to infer the ilmenite content of different formations. In the current paper, using frequency attributes, we detect a sequence of basaltic layers down to m depth with varying thickness and ilmenite content. Three distinct volcanic phases are observed based on their ilmenite content. These far‐side observations point to a volcanic activity with a time‐dependent variation in titanium content, consistent with trends documented in other areas of the Moon.