Chang'e-4 data reveals hidden crater beneath Moon's surface

This science device's primary function is to track radio waves beneath the surface in order to produce a precise lunar subsurface map. It does this by allowing the rover to transmit radio signals deep below the lunar surface. Furthermore, it catches radio waves that bounce off underlying structures in order to produce a map. 

"The GPR sends electromagnetic pulses into the lunar interior and receives echoes from subsurface layers," said the study.

This time, the team utilized LPR to image the moon's top 1,000 feet of surface in the South Pole-Aitken Basin. The rover has earlier collected data on the top 130 feet of the lunar surface. 

According to these new findings, the first 130 feet of the lunar surface are composed of numerous layers of dust, silt, and shattered boulders.

The data analysis also revealed the presence of a buried impact crater that was left out when a big object collided with the moon and is now concealed beneath this strata.

Layers of lava beneath the surface

Farther below the top 130 feet, scientists uncovered five unique layers of lunar lava that flooded the lunar surface during its turbulent initial years some billions of years ago.

The formation of the moon was a highly volatile event when a Mars-sized space rock slammed into Earth at high speed. As a result, it broke off a large chunk of our young planet some 4.51 billion years ago, resulting in the formation of the moon. 

During its early years, the moon was also pummeled with other celestial huge rocks, with evidence left on its surface in the form of massive impact blotches. 

Some of these impacts were so powerful that they caused fissures in the newly formed moon's surface. “Like Earth, the moon’s mantle at that time contained pockets of molten material called magma, which seeped out through the newly formed cracks in a series of volcanic eruptions,” noted the report.  

The latest Chang'e-4 data suggest that the process is slowed down as the moon started to cool with time. Moreover, the team discovered that the layers of volcanic rock grew thinner as they got closer to the moon's surface. This shows that subsequent eruptions produced less lava than earlier ones.

“The thickness of the strata decreases with the decreasing depth, suggesting a progressively smaller lava effusion rate over time,” mentioned the study. 

According to the researchers, when the Moon slowly began to cool down, its energy decreased over time, as depicted by the decreased lava flow in the upper layers. 

The findings were published in the Journal of Geophysical Research: Planets. 

Study abstract:

We revealed the layered structure of the upper three hundred meters of the lunar surface in the South Pole-Aitken Basin by using the measurements from the Lunar Penetrating Radar (LPR) onboard the Chang'E-4 rover. The result shows that five large strata are identified by the LPR 60-MHz channel below the depth of 90 m, with thicknesses ranging from 20 m to larger than 70 m. We speculate that at least three strata are basalt flows, while the shallowest stratum is composed of multiple thin lava flows. The thickness of the strata decreases with the decreasing depth, suggesting a progressively smaller lava effusion rate over time. To evaluate the reliability of the result, a comparison was made between Chang'E-4, Chang'E-3, and ground test low-frequency data. The LPR 500-MHz channel unveiled the structure of weathered material in the top ∼40 m, revealing several layers as well as a buried paleo crater and its ejecta blanket in the regolith.