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China's Chang'e probe discovers what's lurking beneath moon's far side

The first spacecraft to touch down on the far side of the moon takes a peek below the surface.

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- 03:15
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The Chang'e 4 lander on the far side of the moon.

CSNA

It's awfully lonely for the Chang'e 4 lander and rover on the far side of the moon, but there's also a ton of opportunity over there. As the only spacecraft to ever touch down on the surface, Chang'e 4 has been revealing the secrets of the moon's other face for almost a year. It's rover, known as Yutu-2, has uncovered a strange gel-like substance and taken stunning pictures of the surface but new research shows the plucky, lonely rover has also been investigating what lies beneath.

The Chang'e 4 mission has spent over a year on the lunar surface, touching down on the far side in January 2019 and releasing Yutu-2 on the flat, desolate plains of Von Kármán crater, a big impact structure that lies in the South Pole-Aitken basin. Equipped with a penetrating radar, Yutu-2 is able to send out pulses of radio waves through the surface of the moon, which are then bounced back off soil and rock to paint a picture of the moon's underworld.   

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In a paper published in the open-access journal Science Advances on Wednesday, a collaboration of researchers from the Chinese Academy of Sciences and institutes across Italy and China has provided the first subsurface details from the moon's far side. Using the penetrating radar over two lunar days of study, the team was able to map a depth of up to 40 meters below the surface, revealing the geologic features present.

The far side of the moon is a bit of a punching bag. The surface is highly-cratered because over the period of about 4.5 billion years, its been smashed by impacted by roaming space rocks. The South Pole-Aitken basin is one such impact crater and that's what makes the results from Chang'e 4 so exciting -- they can provide information about the cosmic collision and reveal more about the minerals within.

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A diagram of the moon's underbelly, as detected by the Yutu-2 rover.

CLEP/CRAS/NAOC

Chang'e 4's radar shows three distinct layers of the lunar surface in the crater. On top is the lunar regolith -- a fine, loose layer of rock that extends approximately 12 meters below. That far down there's a layer of much bigger rocks and boulders, likely kicked up and settled after an impact event. The bottom layer starts at around 24 meters down and seems to contain finer dust and larger rocks.

The team believes this layering was created during the formative years of the galaxy, when space was a lot less serene. It's likely the moon was constantly struck, forcing material to be ejected from its surface and then settling back on the surface. Such activity could create the layering seen, with each impact causing a different distribution of rock and soil.

China's previous lunar explorer, Chang'e 3, landed on the other side of the moon -- the one facing Earth. It also took images of the subsurface but was not able to reach the same depths as Chang'e 4. 

"We found that the signal penetration at the [Chang'e 4] site is much greater than that measured by the previous spacecraft, Chang'e-3, at its near-side landing site," said Li Chunlai, deputy director-general of the National Astronomical Observatories of the Chinese Academy of Sciences and author of the new paper, in a press release. The lack of radar penetration with Chang'e 3 suggests the two landing sites have a totally different composition of rock and soil.

With this new look at the moon's mysterious far side, scientists take another leap forward in understanding how impacts and lunar volcanism may have shaped our celestial sister. And the party doesn't stop there.

China is looking to expand upon its Lunar Exploration Program with the launch of another lunar explorer towards the end of the year, Chang'e 5. The country will attempt to send another lander to the surface of the moon, in the hope of retrieving samples of the fine soil that makes up the surface and bringing them back to Earth.