Different "aliens" were found on the moon's surface, which may provide them with water

Are there "aliens" on the surface of the moon? Can "aliens" provide water for the moon? Based on the ultra-high spatial resolution images and spectral data obtained by Chang'e-4, researchers from the National Space Science Center of the Chinese Academy of Sciences and other institutions have identified for the first time on the surface of the moon the remnants of carbonaceous chondrite impactors that are less than one million years old. Studies have shown that the impact of carbonaceous asteroids rich in volatile components may still provide water for the current moon. At the same time, relatively young lunar surface materials (such as the samples returned by Chang'e-5) may contain remnants of impactors. The relevant research results were published in Nature Astronomy.

Yutu-2 conducted a detailed spectral detection of a small fresh impact crater that it "encountered" during its patrol path. Image source: CCTV News

"Direct analysis of impactor remnants that may be present in Chang'e-5 samples will provide important references for the evolution of the composition and types of impactors in the Earth-Moon system, and is expected to further constrain the orbital dynamics of the solar system and enhance our understanding of the impact history of the inner solar system," Liu Yang, a researcher at the National Space Science Center of the Chinese Academy of Sciences, told Science and Technology Daily on November 30.

Carbonaceous chondrite impact remnants found on lunar surface for the first time

The Chang'e-4 probe successfully landed in the Von Karman crater in the South Pole-Aitken Basin on the far side of the moon in January 2019. The Yutu-2 rover it carried subsequently conducted continuous patrol and exploration of the lunar surface, acquiring ultra-high-resolution lunar surface images and hyperspectral data.

Liu Yang said that during the lunar surface patrol, "Yutu-2" discovered a small fresh impact crater and conducted detailed spectral detection of the impact crater.

Based on the crater images and spectral data, the research team found that the suspected "residues" in the center of the crater showed significantly different spectral characteristics from the typical lunar soil and rock fragments inside and outside the crater.

Liu Yang explained that under normal circumstances, the reflectance spectrum of lunar surface rocks or lunar soil will show a "reddening" feature, and space weathering on the lunar surface will generally further aggravate this reddening feature, that is, the reflectivity increases with increasing wavelength; however, the spectrum of suspected residues in the center of the crater shows a "bluing" feature, that is, the reflectivity decreases with increasing wavelength.

Therefore, the research team speculated that there may be some kind of foreign impactor material with blue spectral characteristics mixed into the impact crater. "In the past, researchers have found carbonaceous chondrite fragments in the 'Apollo samples', but have never directly observed the impact residues of carbonaceous chondrites on the lunar surface through remote sensing detection. This is the first time that the impact residues of carbonaceous chondrites have been directly observed on the lunar surface." Liu Yang pointed out.

In fact, among asteroids, only carbonaceous asteroids have blue spectra. The researchers collected a large number of spectra of carbonaceous chondrites and found, after careful comparison, that the residue is indeed highly similar to the spectra of carbonaceous meteorites.

Water in the impactor body may be retained in the impact melt or residue

To confirm the analysis results, the research team conducted a detailed morphological analysis of the crater.

"Based on the stereo images obtained by the panoramic camera of 'Yutu-2', our team used photogrammetry to construct a high-precision digital elevation model covering the small impact crater and the surrounding area," said Liu Yang.

Analysis shows that the crater may be a primary impact crater, rather than a secondary impact crater formed by the ejecta produced by the original impact hitting the lunar surface again.

To further qualify the results, the researchers also used numerical simulation techniques to study the impact crater. The results showed that a loose impactor with a diameter of 15 cm hitting the lunar surface at a speed of 15 km/s could form the observed small impact crater morphology, with residues distributed in the center of the impact crater.

"In this way, we can confirm that the impact crater should have been formed by the impact of a small carbonaceous meteorite," Liu Yang emphasized.

The impact transport process is considered to be one of the main contributors to water on the lunar surface and water ice in the permanently shadowed areas. Carbonaceous asteroids are a type of asteroid that is relatively rich in water and volatiles. During the impact process, some of the water they carry may be retained on the lunar surface.

Liu Yang said that previous high-speed impact simulation experiments conducted on the ground found that water in the impact body may be retained in the impact melt or residue.

Based on the crater degradation model, the research team estimated the age of the crater, and the results showed that the crater should have been formed within one million years.

More importantly, 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 the Chang'e 5 samples.

Liu Yang said that by using remote sensing spectral data with higher spatial resolution, it is possible to discover more similar impact residues on the lunar surface in the future, thereby further deepening the research on the source of lunar water.

◎ Science and Technology Daily reporter Lu Chengkuan

Source: Science and Technology Daily

Editor: Wang Yu

Review: Yue Liang

Final review: Liu Haiying