The Chang'e 4 lander and the "Yutu 2" lunar rover finished their 22nd month day work at 7:30 on September 24 and 23:18 on 23rd, respectively. They completed the moon night mode setting according to ground instructions and entered moon night sleep. Up to now, Chang'e-4 has spent 630 Earth days on the back of the moon and traveled 547.17 meters cumulatively.
Based on the 21st month day panoramic camera stitched image, DOM image and other data, the "Yutu 2" lunar rover mainly traveled during the 22nd day of the month, successively in the impact crater and reflection about 1.3km northwest of the landing site Areas with higher rates were detected.
Researchers have made use of data such as panoramic camera ring-shot detection, infrared imaging spectrometer calibration detection, and simultaneous detection of lunar radar during driving, and have obtained a number of scientific results, which were recently published in the international journal Nature Astronomy.
The scientific team conducted in-depth research on the radar detection data and obtained important discoveries about the lunar soil and shallow structures in the landing zone. Based on the characteristics of low-frequency radar signals, as shown in Figure 1, the shallow structure of the landing area is divided into three basic units, from top to bottom, there are strong reflection units (unit 1), weak reflection units (unit 2) and medium reflection units. Unit (Unit 3).
Combining the basic constraints of regional geology and the spatial distribution of large-scale impact craters, the results of the geological interpretation are as follows: Unit 1 (total thickness of about 130m) is the accumulation of sputtering materials adjacent to multiple impact craters (including Finsen, Alder, and von Carmen). Impact craters such as L and L') and the basalt breccia layer at the bottom; unit 2 (total thickness of about 110 m) is a basalt layer with multiple eruptions; unit 3 (thickness not less than 200 m) is Leibniz in the northern part of the landing zone Spatter from impact craters.
The high-frequency radar signal further gives the fine structure of the upper part of the unit 1, which is characterized by the presence of a 12m thick lunar soil layer on the top, which basically does not contain large rocks, and the bottom is a strip of 22m thick Sputters, they are all projectiles from the Finsen impact crater, with a total thickness of 34m.
The lunar radar carried by the "Yutu-2" lunar rover can obtain the geological section below the driving path and reveal the layered structure of the underground. Because the lunar radar is directly based on the lunar surface for detection, the reflected signal detected by it has large energy and clear characteristics, and its effect is far better than that of spaceborne radars more than 100km away from the lunar surface.
Moreover, due to the use of a frequency much higher than 5MHz of the spaceborne radar, its resolution advantage is also very obvious. The main frequencies of the two channels of the lunar radar are 60MHz and 500MHz, the spatial resolution is 10m and 0.3m, and the detection depth is about 50m and 500m. The high-frequency channel is used to detect the high-resolution structure of the shallow lunar soil and its underlying sputter, and the low-frequency channel is used to detect the layered structure of the deep sputter and basalt.
The shallow structural profile obtained by the lunar radar shows that the lunar material detected by "Yutu 2" comes from the Finsen impact crater, not from the filling basalt of the von Karmen impact crater; at the same time, the radar profile also reveals The landing zone experienced multiple impacts, sputtering accumulation and multiple basalt magma eruptions filling. These new discoveries are of great significance for understanding the evolution of the Moon’s South Pole-Aiken Basin, and have an important guiding role for the subsequent exploration and study of the composition and structure of the Moon’s internal matter.