The first detailed picture of what lies beneath the far side of the Moon provides a new glimpse of our closest neighbour's violent past.

Key points: Chang'e-4 is the first spacecraft to land on the far side of the Moon

Chang'e-4 is the first spacecraft to land on the far side of the Moon C4's rover Yutu-2 took detailed radar images of what lies beneath the smooth, dusty moonscape down to depth of 40 metres

C4's rover Yutu-2 took detailed radar images of what lies beneath the smooth, dusty moonscape down to depth of 40 metres Understanding the fine detail of what lies below the surface tells us about the Moon's history as well as provides information for space exploration

We know a lot about the side of the Moon facing us, but no spacecraft had landed on the far side until the Chinese probe Chang'e-4 touched down just over a year ago.

Within hours, the spacecraft's rover Yutu-2, or Jade Rabbit 2, started trundling across the dusty moonscape using penetrating radar to probe beneath the surface.

Data from the first two days, published today in the journal Science Advances, builds a picture of layers of fine dust and dirt interspersed with jumbled boulders and rocks deposited by multiple meteor strikes going back billions of years.

It is the most detailed cross-section of a series of meteorite impacts on the Moon ever produced, said the Chang'e-4 team.

"This work shows the extensive use of the [lunar penetrating radar] could greatly improve our understanding of lunar impact and volcanism, and shed new light on the ... geological evolution of the Moon's far side," they wrote.

Welcome to the far side

Map showing the South Pole-Aitken basin (in purple) on the far side of the moon. ( Supplied: NASA )

The far side of the moon looks very different to the side we see.

Pummelled by thousands of meteorites over its 4.5-billion-year lifetime, it is rougher and the crust is thicker.

Change-4 landed in the Von Kármán crater in the South Pole-Aitken basin — stretching across 2,500 kilometres and extending down 13km, it is the largest, deepest and oldest feature on the Moon.

"It's really exciting to have sent a rover into South Pole-Aitkin basin," commented Gretchen Benedix, a planetary scientist at Curtin University.

It is here that scientists hope to uncover clues about the basin's age as well as discover new minerals unearthed by the force of the massive impact that created it billions of years ago.

Peering beneath the surface

Ground-penetrating radar pings radio waves through the top layers of soil and measures the time it takes them to bounce back.

The technique was first used in 1972 by the Apollo 17 orbiter to map the structure of the Moon's crust to a depth of about 1km under parts of the near side.

It was used 30 years later by the Japanese Kaguya spacecraft to map beneath the far side of the moon to a depth of about 50km.

"The previous measurements indicated different layers, but they don't seem to have come up with the level of detail about the physical properties of the subsurface that Chang'e-4 is producing," Professor Benedix said.

Like other parts of the Moon, the surface of the Von Kármán crater is loosely packed grains of dust and dirt. ( Supplied: CNSA/CLEP/Doug Ellison )

The top 12 metres is made up of fine dust and dirt crushed by the impact of meteorites and weathered by solar radiation.

Underneath this layer lies a second 12m-thick section thought to be rocks and boulders ejected from the creation of a nearby crater 3.2 billion years ago.

Below that are several layers of dust and rocks from many more meteorite strikes. While the radar bottomed out at 40m, the Chang'e-4 scientists speculate that this section continues further down.

Marc Norman, a planetary geologist at the Australian National University, said the layering of dust, dirt and rocks is akin to what we've seen elsewhere on the Moon, where a process known as impact gardening has shaped and reshaped the surface.

"But we certainly didn't know what the structure was at this individual site," Dr Norman said.

The geology of this site did appear to be slightly different to a crater on the near side explored by the first Chinese rover mission Chang'e-3, said Professor Benedix.

While that site was also a layer cake of loose dust and rocks, radar images bottomed out at 10 metres.

"It may not be that the rock compositions are necessarily different, but the physical properties of the rocks are different."

Understanding the fine detail of what lies beneath individual sites could help build a picture of the whole Moon, she added.

An important tool for exploration

The Chang'e-4 mission is looking for signs of ancient rocks on the far side. ( Supplied: CNSA/CLEP/Doug Ellison )

One of the things the scientists are looking for is basalt from the Moon's mantle — the layer between the crust and the core — exposed by the original impact that formed the South Pole-Aitken basin.

"It's been a Holy Grail for a long time to find something that represents direct mantle," Dr Norman said.

While the Chang'e-4 scientists previously reported they may have found basalt in the Von Kármán crater, they have now pulled back from those claims.

They hope more radar surveys using lower frequency wavelengths might penetrate below the 40-metre mark to reveal the basalt bedrock deep below.

"As more data are accumulated, confident stratigraphic structure of the basalt layers will be obtained," Dr Yan Su of the Chinese Academy of Science said.

Not only can finding basalt tell us about the age of the biggest impact on the Moon, it can also tell us about how the solar system formed.

It may also contain unique mineral deposits that could be exploited.

A number of nations have been eyeing off the far side for a space base since the discovery of ice in craters in the southern-most part of the basin.

"These ices could be very useful for generating fuels, for generating consumables and for supporting human exploration," Dr Norman said.