A New Perspective About The Lunar Cryptomare Revealed By CELMS Data

The lunar surface experienced an extremely high impact flux during the early formation of the solar system.The ancient basaltic materials were easy to be buried and covered by the crater ejecta,forming cryptomare.Cryptomare records early lunar volcanism during 3.8 to 4.35 Ga,which is crucial to understand the global history of lunar thermal evolution and magma evolution.However,the current researches on lunar cryptomare are mainly based on the visible-near-infrared data.In addition,the penetration depth of these data is very small,which greatly limits their applications in the study of lunar cryptomare.In Chinese lunar exploration project,a lunar microwave sounder(CELMS),operating at 3.0 GHz,7.8 GHz,19.35 GHz and 37.0 GHz channels,was aboard the Chang’E(CE)satellites with the purpose of measuring the brightness temperature(TB)of the lunar regolith.The penetration depth of the used microwave can be up to several meters.Moreover,the CELMS data has been proved to be sensitive to the compositions and temperature of the substrate regolith,which provides a new data and method for study of lunar cryptomare.Based on CELMS data,the main objective of this paper is to detect lunar cryptomare.Firstly,combined with radiation transmission model and layered lunar regolith model,the TB variation of lunar cryptomare under shallow cover is numerically simulated,which provides a theoretical support in our research;In order to evaluate the microwave thermal emission features in the four research regions,the Chang’E-2 CELMS data was selected and used,which was processed by the hour angle correction,data selecting,interpolation,normalized TB,TB difference(dTB).On this basis,according to the TB and TB difference(dTB)performances at different frequencies,the TB distribution characteristics of the four cryptomare regions were systematically analyzed,moreover,the spatial distribution characteristics of the lunar cryptomare are re-recognized.The main work of this paper is as follows:1.Combined with radiation transmission model and layered lunar regolith model,a passive microwave radiation transmission model for cryptomare is established.The numerical simulation results show that the CELMS data is feasible to identify the cryptomare unit with a certain buried depth.2.By comparing the TB maps,the normalized TB maps and dTB maps of Mare Australe,we found that the 3.0 GHz dTB map can better eliminate the influence of topography and surface temperature,which is conducive to the identification of basalt units.3.In Region 2 of Mare Australe,the possible cryptomare unit may be widespread,which is beyond the recognition based on visible data.4.In Balmer-Kapteyn region,the burial depth of cryptomare in the midwest part is relatively shallow,and that in the southeast part may be a fake cryptomare.5.In Lomonosov-Fleming region,it is found that the cryptomare range defined by microwave data is quite different from that based on the optical data.The new cryptomare regions are mainly located in the southwest of L-F region with a large area of continuous distribution.6.The cryptomare were found on the northwest side of SchillerSchickard region and the inside of Schickard crater,while the southern unit may be the lunar highland with the surface covered by high irontitanium materials.These special findings will be of great significance to better understand the evolution history of lunar surface magma.