The Far Side of the Moon Was Volcanically Active, New Studies Confirm

Scientists analyzed the first and thus far only rock samples from the far side of the moon to understand how the area differs from the familiar near side

The moon takes the same amount of time to orbit around our planet as it does to rotate around its axis, which means that from Earth we can only ever see the same side of the moon. Though this near side has been studied via telescopes, crewed missions, orbiting spacecrafts and more, the scientific community has had far fewer opportunities to study its mysterious counterpart.

Out of sight, however, doesn’t always mean out of mind. In June, China’s Chang’e 6 lunar lander returned to Earth with the first soil samples ever collected from the far side of the Moon.

Now, two studies of the samples published in the journals Nature and Science have just confirmed that the moon’s other half had active volcanoes billions of years ago.

Two discoveries achieved via studies of lunar rock samples retrieved by China's Chang'e-6 spacecraft were published in leading scientific journals on Friday, revealing two volcanic events that occurred on the moon's far side 2.8 billion years ago and 4.2 billion years ago. pic.twitter.com/kPDiodKebA

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“Imagine having rock samples from maybe ten locations in North America, and that’s what you know about Earth,” Stephen Elardo, a planetary scientist at the University of Florida in Gainesville who was not involved in the studies, tells Science News’ Lisa Grossman. “Then all of a sudden you get your first rocks from South Africa or Australia. Now you get to have that as another data point to learn about the whole planet. That’s basically what this is for the moon.”

While scientists already knew of ancient volcanic history on the moon’s near side, previous research had hypothesized the presence of long-extinct volcanoes on the far side as well. These two studies now confirm it.

The more than four pounds of lunar soil included fragments of basalt (a type of volcanic rock), most of which the scientists dated to approximately 2.8 billion years ago via radioisotope dating, which analyzes the rate of radioactive decay. A single basalt fragment dates to about 4.2 billion years ago, and is the oldest known lunar basalt sample brought back to Earth.

Moon's far side once had erupting volcanoes, scientists find

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“To obtain a sample from this area is really important because it’s an area that otherwise we have no data for,” Christopher Hamilton, a planetary volcano expert at the University of Arizona who was not involved with the research, tells the Associated Press’ Adithi Ramakrishnan.

The age of the far side samples indicate that region of the moon had volcanic activity 4.2 billion years ago and 2.8 billion years ago—and during the period in between. Near side samples had previously suggested that the moon experienced volcanic activity from around 4 billion years ago to about 3 billion years ago, per Science News’ Lisa Grossman.

Both teams of researchers also noted that the 2.8-billion-year-old basalt samples had relatively low levels of KREEP—potassium (K), rare-earth elements (REE) and phosphorus (P)—which contrasts with higher levels in near side lunar samples. The decay of radioactive materials in KREEP creates heat, and it could have driven the prolonged duration of volcanic activity on the visible side. But scientists aren't sure, without high levels of those elements, how the far side stayed molten for so long, Elardo tells Science News. 

“The relatively young age of the basalts (retrieved by Chang’e-6) is surprising along with the composition being practically devoid of radioactive elements,” Clive R. Neal, a planetary geologist at the University of Notre Dame and co-author of the Science study, tells CNN’s Katie Hunt. It “prompts the question ‘how and why were these magmas generated,’” Neal adds

“The asymmetry between the Moon’s near side and far side remains an unresolved mystery,” says Qiu-li Li, a co-author of the Nature paper and a researcher at the Chinese Academy of Sciences’ Institute of Geology and Geophysics, to CNN. The China National Space Administration will allow international scientists to apply to study the samples. Further research might one day explain the differences between the two sides of the Moon.

Margherita Bassi | READ MORE

Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.