A little about the hidden side of the Moon

In 2019, China was the first country to land on the hidden side of our satellite. It brought samples back to Earth on Tuesday with a second mission, Chang’e 6, on the far side. Is the Middle Kingdom beating Uncle Sam in the race for the Moon?

Why bring back samples from the far side of the Moon?

Because it is home to the deepest impact crater on our satellite, the South Pole Aitken Basin (SPA). “The asteroid that created it was so large that it probably brought rocks from beneath the lunar crust to the surface,” says Ed Cloutis, a geologist at the University of Winnipeg who is analyzing rocks. moons brought back by Apollo. “It will allow us to better understand the formation of the Moon. »

If the impact did not bring rocks beneath the crust to the surface, it means it is thicker than expected. It will then be necessary to revise the models of formation of the Moon, explains Mr. Cloutis.

The material brought to the surface by the impact that created the SPA basin was located more than 80 km deep, twice as deep as the second largest lunar crater. The SPA basin is the largest known impact crater in the Solar System, with a diameter of 2500 km. It was created more than four billion years ago.

Could samples from China’s Chang’e 6 space probe be useful for a human mission?

Probably not, according to Mr. Cloutis. “Perhaps if we find water easily accessible, but the disadvantages of communication delays are very great. »

What have lunar samples reported in the past revealed?

“Even though the Moon has no atmosphere, many things can change the appearance of its rocks,” says Cloutis. There are asteroids, the solar wind. With the samples, we began to separate the effects of geology and these factors. »

What other missions are planned towards the hidden side?

None are on the menu. NASA proposed one 25 years ago, identical to Chang’e 6. In 1962 the impactor Ranger 4 of NASA crashed on the far side, but was unable to send scientific data.

Why is it called “hidden side” or “dark side”, like the title of a Pink Floyd album?

Because it is always opposed to Earth. Moreover, the far side of the Moon receives light from the Sun and is not always dark.

Why is China the first country to work on this?

“Chang’e 6 is the most complicated robotic lunar mission ever carried out by a country,” explains Brian Harvey, an Irish political scientist who has published several books on the Chinese space program. Communications must be relayed by lunar orbiters, which increases the transmission delay, notably complicating the moon landing.

Chang’e 6 was not part of China’s lunar program, says Mr. Harvey. But after the success of Chang’e 4, which landed in the SPA basin in 2019, it was decided to use a spare lander from the Chang’e 5 mission (which brought back lunar samples in 2020) to bring back samples from the far side, during the Chang’e 6 mission.

Why did China target the dark side?

Probably because no country had done it, according to Mr. Cloutis. “The difficulty of the mission demonstrates China’s technical capacity. »

Mr. Harvey adds that the Tianwen-3 mission, which is expected to bring back Martian rocks in 2030, will be relatively similar. This means that China could be the first country to bring back Martian rocks, because the mission which is to bring back the Martian samples gleaned by the American rover Perseverance is currently being questioned because of its cost.

Is China sharing its lunar samples with Western researchers?

“Samples of Chang’e 5 have been offered to researchers from all countries,” says Mr. Cloutis. I plan to ask for and receive some. »

Could China claim territory on the Moon?

This is a possibility mentioned by the big boss of NASA in 2023 in the magazine Politico, where he spoke of a “race to the Moon”. Bill Nelson cited Chinese territorial claims in the South China Sea as an example.

“He knows the importance of having political support from Congress and the funding that comes with it,” Mr. Harvey said. China announced its space program until 2050 in 2009. It is very transparent. »

Mr. Harvey does not believe that China is engaged in a race to the Moon. A better comparison, he said, would be the cooperation of several countries, including China, in Antarctica.