Compositional variations along the route of Chang\u2019e-3 Yutu rover revealed by the lunar penetrating radar

Chunyu Ding,Zhiyong Xiao,Jun Cui,Yan Su,Jiannan Zhao

doi:10.1186/s40645-020-00340-4

Abstract

Using the high-frequency lunar penetrating radar data obtained by the Chang’e-3 mission, we apply the frequency-shift method to calculate the decay rate of the electromagnetic wave in the regolith-like ejecta deposits of the Ziwei crater. The radar data are divided into segments according to the navigation points along the traverse route of the Yutu rover. For each segment, we calculate the bulk loss tangent of materials within the top ~ 50 ns of the radar data based on the frequency decreasing rate of the electromagnetic wave. The loss tangent varies from ~ 0.011–0.017 along the route of Yutu, and it is within the range of the measured loss tangent of Apollo regolith samples. Using the empirical relationship between loss tangent and TiO2 + FeO content derived from the Apollo lunar samples, we estimate the TiO2 + FeO content for the bulk regolith along the route of Yutu, which is ~ 23–30 wt.%. This value is comparable with that estimated using both orbital reflectance spectral data and in situ observation made by the Yutu rover. The loss tangent derived along the route of Yutu is larger than the average value of returned lunar samples, which is mainly caused by the larger content of TiO2 + FeO at the landing site compared to the global average. Variations of the TiO2 + FeO content along the route of Yutu are mainly due to the excavation of the Ziwei crater. The TiO2 + FeO content map derived by the radar has a much higher spatial resolution compared to orbital observation, testifying the feasibility of this technique for regional geology study.

Highlights

Most of our knowledge about the composition of the Moon is derived from orbital observations, since the number of both returned lunar samples and collected lunar meteorites is still rather limited
The rate of energy decay of electromagnetic waves in lunar regolith is mainly controlled by the content of TiO2 + FeO (Strangway et al 1977), so that the loss tangent of lunar regolith derived from the energy decay rate of electromagnetic waves can be used to estimate the amount of TiO2 + FeO (Campbell et al 1997)
We introduce the data obtained by the CE-3 highfrequency Lunar penetrating radar (LPR) in the “Data” section, the frequency-shift technique used to estimate the loss tangent of lunar materials and the method used to derive the TiO2 + FeO content are introduced in the “Estimate of loss and tangent”

Summary

Introduction

Most of our knowledge about the composition of the Moon is derived from orbital observations, since the number of both returned lunar samples and collected lunar meteorites is still rather limited. Pommerol et al (2010) noticed that radar echoes returned from high-Ti regions on the Moon were low, which were detected by the lunar radar sounder onboard the Selenological and Engineering Explorer Kaguya mission. Applying this method, Campbell et al (1997) estimated the bulk composition of regolith in the lunar mare using Earth-based radar data. This work utilizes the CE-3 LPR data to derive the composition along the route of Yutu, which will fill the observation gap in terms of the spatial resolution between the orbital (e.g., Zhao et al 2014) and in situ measurements (e.g., Wu and Hapke, 2018). Instead of probing only the top-most materials, the LPRderived contents of TiO2 + FeO represent the average value of materials within the radar detection ranges

Results

Discussion

Conclusion