Confirming the moon’s past from its dark side with Chang’E-4

An image of the Chang-E'4 rover.
An image of the Chang-E'4 rover.

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Article by: Keisha Kwok, on 3 September 2023, at 12:47 PDT

A collaborative team of space scientists from the Planetary Science Institute, in partnership with researchers from the Chinese Academy of Sciences, Shenzhen University, and the University of Aberdeen, has delved into lunar history using data provided by China's Chang'E-4 rover. Their study centred on the analysis of lunar-penetrating radar (LPR) data transmitted by the rover.

One of Chang'E-4's major goals is to detect mantle material on the moon's far side. Since 2018, China's Chang'E-4 rover has been these previously uncharted territories. Along its journey, it has been emitting radio signals downward using its LPR equipment. This device has the capability to detect and record signals that are reflected back, essentially functioning as a radar system.

In 2019, another group of researchers employed a subset of this data to create a subsurface map, providing insights into the moon's structure up to 40 metres beneath the surface. In this latest endeavour, the team has taken this effort to new depths, crafting a subsurface map that extends a remarkable 300 metres below the lunar surface.

Their findings revealed that the uppermost 300 metres of the moon's surface comprise various layers of material, including fragmented rock, dust, and soil. The researchers also uncovered indications of a concealed crater. Further below, they identified layers of solidified lava—a piece of evidence to the moon's history of volcanic activity.

Previous studies had suggested that the moon was formed around 4.5 billion years ago, believed to be the result of a colossal collision between a massive celestial body and Earth, propelling fragments of both planets into orbit, which gathered to form the moon. It is theorised that, subsequently, another large object impacted the moon, causing fractures on its surface and enabling molten material to rise to the outer layer.

The insights from Chang'E-4's data corroborate this theory. Examination of the lava layers demonstrated a consistent pattern of decreasing thickness in each successive layer upwards, indicative of gradual cooling and sealing of fissures. The moon is thought to have ceased its volcanic activity approximately 1 billion years ago, and it's now considered geologically inactive.

As Chang'E-4 continues its mission, transmitting and receiving radio signals, we may expect more discoveries regarding the details of the moon's volcanic past. The increasing understanding about the moon's composition will be crucial for developing technologies required for the later stages of the program, as well as other projects such as moon mining.

The abstract of the latest research paper with the analysis of Chang'E-4's data can be read here.

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