Credit: CCTV/Inside Outer Space screen grab

China’s lunar rover Yutu-2, or Jade Rabbit-2, is using its Lunar Penetrating Radar (LPR) to investigate the farside’s underground it roams.

A study conducted by a research team led by Li Chunlai and Su Yan at the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) using that data reveals what lurks below the lunar surface.

Their work has been published in the latest issue of Science Advances.

China’s champion – long duration Yutu-2 rover.

Subsurface stratigraphy

The rover’s LPR sends radio signals deep into the surface of the Moon, reaching a depth of over 130 feet (40 meters) by the high-frequency channel of 500 megahertz (MHz). That penetrating capability is more than three times the depth previously reached by the Chang’e-3 lunar probe – Yutu-1 – that wheeled across the Moon at the end of 2013.


Credit: CCTV/Inside Outer Space screen grab

As reported by China’s Xinhua news group this new data has allowed researchers to develop an image of the subsurface stratigraphy of the farside of the Moon.

“We found that the signal penetration at the Chang’e-4 site is much deeper than that measured by the LPR at the landing site of the Chang’e-3 probe on the near side of the Moon,” said Li Chunlai, a research professor and deputy director-general of NAOC.

Credit: CCTV/Inside Outer Space screen grab

“The subsurface at the Chang’e-4 landing site is very complex, and this qualitative observation suggests a totally different geological context for the two landing sites,” Li said.

Credit: CCTV/Inside Outer Space screen grab

Radar echo

Despite the good quality of the radar image along the rover route at a distance of about 348 feet (106 meters), “the complexity of the spatial distribution and shape of the radar features make identification and interpretation of the geological structures and events that generated such features quite difficult,” said Su Yan, also a researcher from the NAOC.

Credit: CCTV/Inside Outer Space screen grab

“The first layer is a fine 12-meter soil layer below the surface. The second layer between 12 and 24 meters under the ground has a lot of stones and the strongest radar echo. It even forms a stone layer and stacks of loose stones. There are three gravel stacks. The third layer is 24-40 meters under the surface. Radar echo shows its dark and bright parts, so there are granules and scattered stones,” said Su in a China Central Television (CCTV) interview.

Credit: CCTV/Inside Outer Space screen grab

The content is likely the result of a turbulent early solar system, when meteors and other space debris frequently struck the Moon. The impact site would eject material to other areas, creating a cratered surface atop a subsurface with varying layers, said Li in the CCTV interview.

Many layers

“We find the ejecta have many layers and each layer is different from each other. It may mean the place has lots of ejecta from impact sites, so history of meteorite impacts here is very complicated. It also shows the Moon was frequently struck by small celestial bodies, and debris will be ejected to bottom of the Von Kármán crater. The ejecta have recorded history of meteorite impact on the Moon,” Li said.

Von Kármán Crater as viewed by the NASA Lunar Reconnaissance Orbiter Camera, or LROC.
Credit: NASA/GSFC/Arizona State University


As the Yutu-2 rover has walked about 985 feet (300 meters), Li said his team expects new discovery in the future.

“We hope it can walk out of the ejecta-covered area. If it can enter a basalt zone, maybe we can better understand distribution and structure of ejecta from meteorite impacts. The distance may be 1.8 kilometers. I think it may take another one year for the rover to walk out of the ejecta-covered area,” Li said.

NASA’s Lunar Reconnaissance Orbiter (LRO) captured China’s Chang’e-4 farside lander/rover.
Image shows lander (near tip of left arrow) and rover (near tip of right arrow) nestled among craters on the floor of Von Kármán crater.
Credit: NASA/GSFC/Arizona State University




Tomographic technique

The scientists analyzed the radar image with tomographic technique, and the result shows that the subsurface is essentially made by highly porous granular materials embedding boulders of different sizes.

China’s Chang’e-4 mission – a lander/rover — made the first-ever soft landing on the eastern floor of the Von Kármán crater within the South Pole-Aitken Basin on the farside of the Moon on January 3, 2019.

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Also, a similar video with different content at:

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