The rover of the Chang'e 4, the first lunar probe that will land on moon's far side. Photo: Xinhua
Yutu is the first lunar probe to land on the far side of the moon. Photo: Xinhua

China’s lunar rover the Yutu-2, the first vehicle of its kind to land on the far side of the moon, has taken samples from deep inside the celestial body that prove it has a mantle and could help unravel the mystery of its composition, formation and evolution.

Data obtained by the visible and near-infrared spectrometer installed atop the Yutu-2 showed that the lunar soil at the landing site of the Chang’e-4 probe contained olivine and pyroxene, believed to be from the lunar mantle deep inside the moon, according to Li Chunlai, chief scientists with the National Astronomical Observatories under the Chinese Academy of Sciences.

Related data, images and analyses have been published in the latest issue of the academic journal Nature.

An in situ investigation on the far side of the moon has identified materials that might have originated from the lunar mantle, and the results could lead to improved models of how the moon formed and evolved, noted the journal.

The moon comprises a core, mantle and crust, just like the earth. With the evolution of lunar magma, the light plagioclase rises to the upper layer to form the lunar crust, while the heavier olivine and pyroxene sinks to form the lunar mantle, Li said.

“But since the lunar crust is very thick, and there has been no volcanic activity and plate movement on the moon for billions of years, it’s hard to find or observe anything from the lunar mantle, whose existence is only theoretical,” Li said.

The composition of the lunar mantle has long been debated. Neither the lunar samples from missions by the United States and the Soviet Union, nor the remote sensing probes orbiting the moon have provided an accurate picture of the composition of the lunar mantle, Li told Global Times.

With the nation’s fourth lunar mission, Chinese scientists this time focused on a special area on the far side of the moon – the South Pole-Aitken Basin – which was formed by a celestial collision over four billion years ago. With a diameter of 2,500 km and a depth of about 13 km, the basin is the moon’s oldest and largest impact crater. Very large impact craters can potentially penetrate through the crust and enable probes to sample the lunar mantle.

Successful soft moon landings and lunar topography. The colored dots represent landing sites of spacecraft on the nearside (left) launched by various countries. The color scale depicts the altitude of the lunar surface. In January, China’s Chang’e-4 made history by landing in a large impact crater on the far side (left). Chang’e-4’s rover, Yutu-2, identified possible mantle-derived materials. Photo: Nature journals

Since Chang’e-4 uneventful soft-landing on January 3, the Yutu-2 obtained and transmitted quality spectral data from the landing site.

Subsequent analyses by Li’s team showed the lunar soil at the landing area contained a large amount of olivine, low-calcium pyroxene and a small trace of high-calcium pyroxene, which are very likely from the lunar mantle.

Then the next question is: how did the minerals deep inside end up on the lunar surface?

The clues are in the high-resolution remote-sensing images as well as hyperspectral data from the Chang’e and Yutu, which suggest that these materials were ejected from craters as “lunar mantel debris” when small asteroids crashed into the area.

He said the study could provide a reference for a future mission to collect and return lunar samples and even the site selection for the construction of a future lunar base.

It was reported by a Chinese newspaper that the Chang’e-6 probe, scheduled to be launched in 2024, will return with the first-ever soil sample from the far side of the moon.

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