Evrim Yazgin
Cosmos science journalist
China’s Yutu-2 lunar rover has peered 300 metres beneath the surface of the Moon, providing finer detail than ever before and revealing “hidden structures.”
Chang’e-4, carrying Yutu-2, landed on the lunar surface in 2018, becoming the first spacecraft ever to land on the “dark side” of the Moon – the side that perpetually faces away from Earth.
Its Lunar Penetrating Radar (LPR), sends radio signals deep into the crust. In 2020, Yutu-2’s LPR was used to peer 40 metres below the Moon’s surface.
The rover then “listens to the echoes dancing back,” lead author Dr Jianqing Feng, astrogeological researcher at the Planetary Science Institute in Tucson, Arizona, explains in an article on Live Science.
By analysing how the radio waves bounce back off structures beneath the surface, scientists are able to build a three-dimensional underground map.
The results of LPR’s investigation are published in the Journal of Geophysical Research: Planets.
The new map shows that the top 40 metres of the Moon’s crust is made up of layers of dust, soil and rocks.
Within this upper layer, the scientists found a hidden impact crater – since covered, the researchers hypothesise, by debris from the collision. Beneath this top stratum are five layers of lava that flowed over the surface billions of years ago.
Scientists have determined that the Earth is 4.543 billion years old. Research also suggests that the Moon hasn’t been Earth’s companion from the very beginning.
It is estimated that the Moon formed 4.51 billion years ago when a Mars-sized ancient planet, dubbed Theia, crashed into Earth. A chunk of Theia became the Moon. Then, the Moon experienced 200 million years of repeated pelting by asteroids as the solar system took shape. Some impacts were forceful enough to break the lunar outer crust and force hot magma onto the surface.
These lava layers are thinner the higher up they are, suggesting less lava flowed out in later eruptions.
“[The moon] was slowly cooling down and running out of steam in its later volcanic stage,” Feng said. “Its energy became weak over time.”
While evidence has been found suggesting lunar volcanism as recently as 100 million years ago, it is believed that the Moon became largely inactive about 1 billion years ago.