Abnormal Subsurface Deposits in Lacus Mortis Uncovered by CE-2 MRM Data

Lacus Mortis, a lunar mare region, exhibits complex and anomalous microwave thermal emission signatures. This study utilizes brightness temperature (TB) data acquired by the Chang'e (CE)-2 Microwave Radiometer (MRM) to investigate the thermophysical properties of its surface and shallow subsurface. Radiative transfer models for two distinct scenarios, including regolith–rock and rock–regolith–rock layered models, are employed to assess microwave emission behavior across Lacus Mortis. These simulations reveal a strong correlation between the TB difference (TBD) and both (FeO+TiO₂) abundance (FTA) and the areal fraction of surface rock coverage. By analyzing the normalized TB (nTB) and TBD maps, the main findings are summarized as follows: (1) Within the Crater unit (Cc), nTB variations are primarily influenced by surface topography (slope orientation). In contrast, TBD is largely controlled by rock abundance (RA), indicating its dominance in driving microwave emission differences. (2) A significant thermophysical anomaly is detected in the Upper Imbrian unit (Im2). Despite high FTA, this region exhibits unexpectedly low TBD at high frequencies (19.35/37 GHz), suggesting the presence of shallow subsurface anomalous material. (3) Through multifactorial analysis and similarity assessment, the detected low-TBD anomaly correlates strongly with tectonic grabens, implying the existence of MgO-rich or other high-thermal-absorption materials. This study highlights the capability of CE-2 MRM data to probe vertical thermophysical structures and composition of subsurface deposits, offering important insights for future mineral exploration on the Moon.