China's Lunar Mission Has Found Mantle Material on the Far Side of the Moon

The Moon’s near (left) and far (right) sides.
The Moon’s near (left) and far (right) sides.
Graphic: Mark A. Wieczorek (Wikimedia Commons)

Scientists in China have released an important first set of results from the Chang’e 4 lunar lander, revealing what appears to be material from the Moon’s mantle on its far side.

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There’s a surprising amount that scientists don’t know about our Moon—specifically the composition of its interior and how it came to look the way it does today. China’s Chang’e 4 mission touched down on the Moon’s far side in January, a first for humanity, with a goal of answering some of these questions. These results provide the first observations from the Yutu 2 rover’s Visible and Near Infrared Spectrometer as it traverses the Moon’s South Pole-Aitken basin. The findings offer a window into both the ancient Moon as well as ancient Earth.

Theories suggest the Moon’s mantle formed as lighter material floated to the surface of a “magma ocean” while heavier material sank, study authors Bin Liu and Chunlai Li from the Chinese Academy of Sciences told Gizmodo in an email. “Understanding the composition of the lunar mantle is critical for testing whether a magma ocean ever existed as postulated,” they wrote.

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The South Pole-Aitken basin is the darker region in the lower half of this image.
The South Pole-Aitken basin is the darker region in the lower half of this image.
Image: NASA/GSFC/Arizona State University (Wikimedia Commons)

The Chang’e 4 lander successfully touched down on the moon on January 3 of this year, and both the lander and its rover began taking data. The rover has since begun exploring the 1,553-mile-wide (2,500-kilometer) South Pole-Aitken basin, an enormous impact crater and candidate for containing material from the Moon’s mantle. Researchers analyzed the lunar soil using data from Visible and Near Infrared Spectrometer, which can determine the identity of the material in the soil based on its spectral lines.

Yutu 2's data revealed dense, iron-rich minerals like olivine and pyroxene in the soil, according to the paper published today in Nature. The researchers took this to mean that they may have found solidified rocks from the mantle—the layer beneath the lunar crust that makes up the bulk of the Moon’s volume—which would have been kicked up after an impact event produced another 45-mile-wide (72-kilometer) crater inside the South Pole-Aitken basin.

Scientists are excited about these results for lots of reasons—many of which don’t directly tie to the actual analysis. “More than the paper, what is exciting is that we went back to the Moon,” Melanie Barboni, assistant professor at the School of Earth and Space Exploration of Arizona State University, told Gizmodo. “We’ve been waiting decades for this. This wonderful group did it, and landed in a place that we’ve never been before... the far side seems to be so different from the near side, and they could be recording so much information that we’re still missing.”

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The Chang’e 4 lander, as photographed by the Yutu 2 rover.
The Chang’e 4 lander, as photographed by the Yutu 2 rover.
Image: CNSA

Additionally, most of the samples taken by missions to the near side of the Moon seem to contain traces from some cataclysmic collision that created the near side of the Moon’s Mare Imbrium (the left eye, if you imagine the Moon, viewed from the Northern Hemisphere, as a face). Nicolle Zellner, professor at Albion College in Michigan, told Gizmodo that she was excited for samples that didn’t contain ejecta from the Imbrium event. New samples allow scientists to better understand the lunar interior, its surface, how material moves around the Moon, and other things, she said.

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This is just a first result, and scientists still don’t know the concentration of these minerals beneath the lunar surface. But the scientists behind Chang’e 4 will continue analyzing these results to try and understand the origin of the materials that they see, according to the paper. Every source I spoke to stressed that this is an exciting time for lunar science, with the Chang’e series of missions happening now and the promise that the United States will return to the Moon in 2024.

Science Writer, Founder of Birdmodo

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DISCUSSION

spacecommunist
Cosmonausicaä

The term is “regolith,” not soil. The creation of soil is largely biological, and at the same time life requires soil for plants to take root and grow. Regolith is inorganic and has more in common with sand, but far more lethal to life than sand. Its specific components and lethality depend on the planet its taken from; Lunar regolith will kill you in a different way than Martian regolith. Note Mars does have some rare soil of its own; its discovery was A Big Deal.

Also the “magma ocean/iron apocalypse” theory of planet formation is not unique to the moon. This is just part of the evolution of planets. You don’t need a lot of mass or size to undergo differentiation; the large asteroid Vesta has, and its the second-largest asteroid in the main belt. That said, the moon probably formed differently from most planetary objects, so the theory is worth confirming, not just to hammer out specifics for the theory but specifics for the evolution of the moon.