Source: China Aerospace Science and Technology Corporation
Recently, based on the images and spectral data with ultra-high spatial resolution obtained by the Chang'e-4 rover (that is, the lunar rover "Yutu-2"), the Chinese scientific research team identified the carbonaceous chondrite impactor residues of less than 1 million years old in situ on the lunar surface for the first time.
The Chang'e series of probes of China's lunar exploration project and the Long March series of carrier rockets used in their launch were developed by China Aerospace Science and Technology Group Co., Ltd., and other subsystems of the project also have the participation of relevant units affiliated to the Aerospace Science and Technology Group. Among them, the Chang'e-4 mission realized the soft landing and inspection of spacecraft on the far side of the moon for the first time in human history, and realized the relay communication between the far side of the moon and the earth for the first time; the Chang'e-5 mission realized China's first extraterrestrial object sampling return, and retrieved the first lunar samples of the 21st century for mankind.
Prior to the Chang'e-4 mission, carbonaceous chondrite meteorite fragments were found in the Apollo sample, but the impact residues of carbonaceous chondrites were never directly observed on the lunar surface through remote sensing. The findings of the research team at the National Space Science Center of the Chinese Academy of Sciences suggest that the impact of volatile carbonaceous asteroids may still provide water for the current moon.
Chang'e-4 rover "Yutu-2"
At the same time, studies have shown the possibility of impactor residues in younger lunar surface materials, such as the chang'e-5 returned samples. The direct analysis of these impactor residues that may exist in the Chang'e-5 sample will provide an important reference for the evolutionary history of the composition and type of impactors in the Earth-Moon system, and is expected to further constrain the evolution of the orbital dynamics of the solar system and improve the understanding of the impact history of the inner solar system. The relevant research results have been published in the international academic journal Nature-Astronomy.
Chang'e-4 lander
The Chang'e-4 probe successfully landed in the von Kármán impact crater in the South Pole-Aiken Basin on the far side of the moon in January 2019, and its "Jade Rabbit II" rover subsequently carried out continuous inspection of the lunar surface. The Yutu-2 is equipped with a panoramic camera and a visible-near-infrared imaging spectrometer that can acquire ultra-high resolution lunar surface images and hyperspectral data.
Chang'e-4 relay star Queqiao supports communication between the Earth and the far side of the Moon (schematic)
During the lunar surface inspection, Yutu-2 discovered a small fresh impact crater and made a detailed spectral detection of this impact crater during the day of the Ninth Month. Based on the close-up images of the impact crater obtained by the panoramic camera, the research team found that there was some material in the center of the impact crater that was significantly different from the crater wall and the lunar soil outside the crater.
The study analyzed the hyperspectral image data obtained by the imaging spectrometer and found that the suspected "residue" in the center of the impact crater showed obviously different characteristics from the spectrum of typical lunar soil and rock fragments inside and outside the crater, and speculated that some kind of foreign impactor material with blued spectral characteristics was mixed into it.
Yutu-2 conducts detailed spectral detection of a small fresh impact crater "encountered" on the inspection path
The study collected spectra of a large number of carbonaceous chondrite meteorites, and after careful comparison, it was found that the residue did have a high degree of similarity with the carbonaceous meteorite spectrum. The analysis suggests that the crater may have formed after the impact of a small carbonaceous meteorite.
The impact transport process is considered to be one of the main contributors to water ice on the lunar surface and in permanent shadow areas, while carbonaceous asteroids are relatively water-rich and volatile groups in small bodies, and the water they carry during the impact may be partially retained on the lunar surface. Based on the crater degradation model, the team estimated the age at which the crater was formed, and the results showed that the crater should have been formed within a million years.
Lunar surface sampling of the Chang'e-5 probe
Direct observations of carbonaceous impact residues suggest that similar carbonaceous meteorite residues may be very common on the lunar surface, and there is a high probability that similar impact residues will be found in samples taken from a relatively young basalt unit on the lunar surface by the Chang'e-5 mission. At that time, combined with the chronological analysis of the main trace elements and isotopes, the evolution of impactor composition and type can be better defined.
In the future, the use of higher spatial resolution telemetry spectral data will make it possible to find similar impact residue distributions in more places on the lunar surface, thereby further deepening the understanding of the origin and distribution of lunar water.
Source: CCTV, china national space administration official website, the fifth academy of the aerospace science and technology group, the national space science center of the Chinese academy of sciences