The moon is Earth’s only satellite and will be the outpost and transfer station for further human space exploration. On December 14, 2013, Chang’e-3 successfully landed on the young and high-Ti lava flow in the northeastern Mare Imbrium (Fig. 1). The Yutu Rover started its in situ experiments with several scientific payloads. China is the third country in the world to have independently accomplished a soft landing on the moon.
In addition to a stereo camera, the Yutu Rover is equipped with three other scientific payloads: Lunar Penetrating Radar (LPR), a Visible and Near-Infrared Imaging Spectrometer (VNIS) and an Active Particle-Induced X-ray Spectrometer (APXS). During the first two months, Yutu performed two experiments on the lunar regolith using APXS and four experiments using VNIS, and obtained a nearly 100-meter-long cross-section using LPR (Fig. 2).
In order to “achieve much more solid scientific research results as soon as possible,” the General Office of Lunar and Deep-space Exploration of CAS established five core teams to concentrate on scientific applications using the exploration data. Prof. LIN Yangting of the Institute of Geology and Geophysics is in charge of the regional geochemistry and tectonic dynamic evolution model for the Chang'e-3 lunar mission.
Prof. LIN’s team closely cooperates with CAS institutes providing payloads (e.g., the Institute of Electronics, Institute of High Energy Physics and Shanghai Institute of Technical Physics, among others) and the Ground Research and Application System for the Chinese Lunar Exploration Program. They established the processing methods for three sets of scientific payload data and determined the chemical composition, mineral composition and structures of both the lunar regolith and shallow lunar crust. These results reveal that the Imbrium Basin has had several large-scale volcanic eruptions during its history, thus helping us further understand the formation and evolution of the moon.
Based on VNIS data, the calibrated spectra of the lunar soil are similar to the laboratory measurements of Apollo Mare soil samples. The chemical compositions of the lunar soil measured by APXS have higher TiO2 (4.0–4.3 wt%) and FeO (21.3–22.1 wt%), but lower Al2O3 (10.5–11.5 wt%) compared to the Apollo and Luna soil samples. The composition of the lunar soil could represent the basalt underneath, as suggested by its high FeO and TiO2 contents.
In addition to identifying major elements, APXS analyses also yielded minor element K and trace elements Zr, Y and Nb, which indicate that the basalts may be mixed with 10-20% KREEP (highly enriched K, REE and P, representing residual melt during crystallization of the lunar magma ocean). A scenario is that the basalt was derived from partial melting of the ilmenite-rich mantle reservoir then contaminated by the residual KREEP layer beneath the ferroan anorthosite crust as it ascended to the surface.
According to the results of LPR, the thickness of this basalt layer is about 195 m, which suggests large volcanic eruptions in the late magmatic activity of the moon, probably due to high concentrations of the radioactive elements U, Th, and K.
In addition, this study also reported the thickness of the lunar regolith at the landing site (~ 5 m), which is significantly thicker than those of previous results by indirect methods. This suggests underestimation of the thickness of the lunar regolith by previous studies. Since the lunar soil is an important reservoir of 3He and H, this result has great influence on the estimation of 3He and H resources.
In contrast with the laboratory analysis on returned samples from the moon, Chang'e-3 performed three in situ analyses on the lunar regolith regarding chemical composition and spectral analysis. This information can provide a calibration for lunar orbit remote sensing data and further improve the accuracy of detection data. Research based on the data returned from Chang'e-3 can help us to further understand the moon.
This research was published in Proceedings of the National Academy of the Sciences of the United States of America (Zhang et al. Volcanic History of the Imbrium Basin: A Close-up View from the Lunar Rover Yutu. PNAS, 2015, 112(17): 5255–5544) as cover story on April 28, 2015.
The lunar rover Yutu (photograph courtesy of the Ground Research and Application System of the Chinese Lunar Exploration Program)
Fig. 1 Chang’e-3 successfully landed on the young and high-Ti lava flow in the northeastern Mare Imbrium (Image by CAS)
Fig. 2 Yutu obtained a nearly 100-meter-long cross-section using LPR (Image by CAS)
Prof. LIN Yangting
52 Sanlihe Rd., Xicheng District,
Beijing, China (100864)