A Chinese probe has returned to Earth carrying the first samples ever taken from the far side of the moon. Chinese state television broadcast images Tuesday of the capsule holding the samples, as it floated down under parachute onto the grassy steppe of Inner Mongolia.
Scientists say the rocks inside the little space capsule could open a new window into how our nearest neighbor formed.
Chang’e 6, which landed on the far side in early June, wouldn’t be the first space mission to send home moon rocks that rewrote textbooks. Samples taken by Neil Armstrong during the Apollo 11 mission in 1969 upended what was then the prevailing theory about how the moon came to be.
Prior to Apollo, researchers had thought that it formed when a bunch of asteroids near Earth gradually glommed together. But the minerals in the moon rocks that the astronauts brought back suggested a much more violent origin story, according to Richard Carlson, director emeritus of the Earth and Planets Laboratory at Carnegie Science in Washington D.C.
“The wisdom now is that something the size of Mars, for example, hit the Earth and spalled off enough material to put it into orbit and form the moon,” he says.
In other words, the giant ball of molten magma that was ripped from the Earth by this collision eventually cooled into the orb we see in the sky.
The theory is widely accepted today, but the evidence remains somewhat limited. That’s because the Apollo missions (as well as the Soviet Union’s robotic Luna missions) all landed on the near side of the moon — the one that always faces the Earth.
“Think about the geology of the Earth: If you only landed in North America, you’d be missing a big part of the story, right?” says Carlson.
China’s latest robotic probe, called Chang’e 6, landed on the far side of the moon. That’s a much more challenging task because the far side faces away from our planet and there’s no direct way to communicate. Instead, Chang’e 6 relied on a satellite orbiting the moon to relay its signal.
Earlier this month it used a drill and scoop to collect samples from a lava flow in an area known as the South Pole-Aitken Basin. Carlson says these new samples should confirm the Apollo-era origin story — that the entire moon was forged quickly around 4.5 billion years ago.
If the Chang’e 6 sample “gives the same age as the stuff from Apollo… then the likelihood is that you’re really looking at a global event,” he says. If not, then the textbooks will have to be rewritten again.
Jim Head, a planetary scientist at Brown University, says that the far side of the moon has many other mysteries as well. Unlike the near side, he says, the far side appears heavily cratered and mostly devoid of lava-flooded areas known as “maria”.
“It’s pretty clear that the far side and the near side have many, many differences,” Head says. “It’s a really critical issue. You can’t understand the origin of a planet with one hemisphere.”
China and the U.S. are in competition with each other these days, including over the moon. Both nations say they want to send humans back to the lunar surface by sometime around the end of the decade.
But China has also offered to share at least some of its new moon samples with American researchers, and NASA is allowing the U.S. scientists to submit proposals. Carlson is all for it:
“Somehow I suspect that international politics doesn’t depend on our models for the origin of the moon,” he says.
NPR's Huo Jingnan contributed to this report.
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