China successfully lands Chang'e-4 spacecraft on the far side of the Moon

Since 1959 only six human missions and 13 space probes have landed on the Moon, all which were on the near side.

Not only does Chang'e-4 represent the first time that anything has been successfully landed on this part of the Moon, the mission also produced the first-ever images from the surface of the far side.

Having launched on 8 December 2018, it was not until Thursday 3 January 2019 that the spacecraft was given the instructions to land. The probe then took images of the landing and when it made landfall.

Because the Moon itself blocks all communication between Earth and the lander, all pictures and data have to be bounced off a separate satellite orbiting the Moon.

A historic moment

At 2.26 GMT, the China National Space Administration (CNSA) confirmed that the lunar probe had touched down in the Von Kármán crater in the unexplored South Pole-Aitken basin.

The basin is the biggest, oldest and deepest crater on the Moon and possibly one of the largest known impact craters in the entire solar system.   

It is thought to have been caused by a massive collision early in the Moon's formation. Scientists hope that the impact may have kicked up bits of material from the Moon's interior.

Scientists will be using Chang'e-4 to first identify any of these mantel rocks, then train instruments on them to study their composition. Researchers are also interested in any molten rock that may have flowed into the crater after its formation. 

This data could help scientists further understand how the Moon was formed.

The spacecraft is also carrying a lunar biosphere experiment, which contains both potato and thale cress seeds, as well as silkworm eggs. 

What is the far side of the Moon?

We often call the far side of the Moon the 'dark' side, but this name is misleading. It does not mean that it never receives sunlight but that the dark side always faces away from us on Earth.

Prof Sara Russell, a Merit Researcher at the Museum studying the evolution of the Moon, says, 'It’s not the dark side as it gets as much light on it as any part of the Moon. It’s just we can’t see it, as one lunar face is always pointing to the Earth.

'That means that in some ways it’s one of the most inaccessible places in the solar system as we can’t see it using any telescope on Earth and can’t communicate there directly.'

This is due to tidal locking, in which the tidal forces of Earth have slowed down the Moon's rotation so that it is now in synch with that of our planet.

It was not until 1959 that the first images of the far side were taken by the Soviet spacecraft Luna 3. The first time any human saw it with the naked eye was in 1968, when the Apollo 8 astronauts orbited the Moon.   

How is it different from the near side?

The Moon's surface is not uniform. The side closest to Earth is covered with more maria, which are large basaltic plains formed by ancient volcanic eruptions - early astronomers thought they were large seas.

The far side is distinguished by far more impact craters. These include the enormous South Pole-Aitkin basin, which is roughly 2,500 kilometres in diameter and 13 kilometres deep, and covers about a quarter of the Moon's surface.

It's a common misconception that the far side is more heavily impacted due to the near side being protected by Earth. Instead it is thought that the Moon has been uniformly hit by asteroids, but the crust on the near side is much thinner.

This means that after an asteroid strike, it is far more likely for volcanoes to erupt and fill in the far side's impact craters, thus smoothing the surface and forming the more prevalent maria seen today.

Rover deployed

Just 12 hours after the success of landing Chang'e-4 on the Moon's surface, the CNSA have now deployed their lunar rover known as Yutu 2, or Jade Rabbit 2. 

This latest mission could help unravel these and further mysteries.