Chinese rover discovers the Moon’s violent past beneath its surface

• The Chinese moon rover Yutu 2 observations show that the far side of the Moon may have had a violent past.
• Data from the Von Karman Crater shows that there are three distinct layers up to 40 meters below the surface.
• Chang’e 4 scientists believe that kind of deposition can’t occur without violent action.

The Chinese moon rover Yutu 2, also called $4, is the first human-made object to land on the far side of the moon. After sending back pictures of unexplored terrain, it’s now looking below the lunar surface — and it doesn’t look pretty.

Below the Moon’s surface lie three distinct layers and according to a new study published in $4, the most likely explanation is violent volcanic eruptions happening over time.

The three layers of the Moon
Chang’e 4 scientists used observations from $4’s ground-penetrating radar instrument as it traversed over the Von Karman Crater. They found that the topmost layer of the crust, up to 12 metres below the surface, is mostly made up of uniform lunar soil, with a few large rocks mixed in.

The soil gets more coarse in the next 12 meters and larger rocks become more common. The final layer, that goes down 40 meters, features alternating bands of coarse material and fine soil with embedded rocks in between.


The Moon’s violent past
According to the study, the structure is indicative of volcanic activity on the Moon. Each layer of lunar sand overlays a past eruption. Over time, they piled up on top of the mare basalts — evidence of ancient volcanic eruptions flooding the Von Karman crater with molten lava 3.6 billion years ago.

"Given such a $4, the most plausible interpretation is that the sequence is made of a layer of regolith overlaying a sequence of ejecta deposits from various craters, which progressively accumulated after the emplacement of the mare basalts on the floor of Von Kármán Crater," it said.

The study points out that the kind of deposition shown by data can’t occur without violent action. “It is accompanied by horizontal shearing and mixing, excavation, and subsurface structural disturbances, especially in areas beyond the continuous ejecta deposits of the source crater,” it said.

These observations shed new insight into the Moon’s history and its evolution. However, Yutu 2 was unable to provide reliable data beyond 40 metres below the surface. The researchers advocate that future missions should include instruments to study the sub-surface to explore further.

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