China’s Yutu 2, the first rover on the far side of the moon, has found matter from the mantle that could help explain how the moon and Earth formed.

The Chang’e 4 probe landed in the Von Karman Crater in the moon’s South Pole-Aitken basin on Jan 3 and the Yutu 2 rover began its investigations using a visible and near-infrared spectrometer to analyze the light reflected from the crater’s surface.

The most important scientific discovery of the probe to date was published online in the latest issue of the academic journal Nature.

The research team, led by Li Chunlai of the National Astronomical Observatories of China, found that the lunar soil in the landing area of the probe contains olivine and pyroxene from the hard mantle inside the moon. Like Earth, the moon has a core, mantle and crust.

“The lunar crust is very thick, and there has been no volcanic activity or plate movement for billions of years. It’s hard to find material from the lunar mantle on the surface,” Li said.

The composition of the lunar mantle has long been a subject of theoretical discussion. The United States’ and Soviet Union’s missions and remote-sensing probes orbiting the moon have not provided evidence of the composition of the mantle.

Chinese scientists focused on the South Pole-Aitken basin, which was formed by the impact of a large object more than 4 billion years ago. With a diameter of 2,500 kilometers and a depth of about 13 km, the basin is the oldest and largest impact crater on the moon.

After Chang’e 4 successfully landed on the Von Karman Crater, the Yutu 2 rover obtained good quality spectral data at two sites, Li said. “The data, unlike that obtained by Yutu on the near side of the moon, gave us a pleasant surprise.”

Analysis said the lunar soil in the landing area contains a large amount of olivine, low-calcium pyroxene and a small amount of high-calcium pyroxene, which likely came from the lunar mantle, Li said.

So how did the matter from deep inside the moon get there?

After analyzing high-resolution remote sensing images and hyperspectral data, researchers determined it was likely ejected from the 72-km-wide Finsen Crater located northeast of the Von Karman Crater.

Li said the asteroid impact that created the Finsen Crater might have been so violent that the materials were knocked into the Von Karman Crater.

He said if the future Chang’e 6 probe can go to the area, it could not only bring back the first samples from the far side of the moon but also material from the mantle.

“Most of the evolution of the moon happened about 3 billion years ago, while the early history of the earth before 3 billion years ago has been erased by geological activity,” Li said. “The moon is like a fossil that gives a glimpse of the early history of Earth.”