Samples from the far side of the moon show the history of ancient volcanoes
The first samples found on the dark side of the moon show that there were once volcanoes there, just as there were on the near side thousands of years ago, according to a new study.
China's robotic spacecraft Chang'e-6 made history in June by retrieving samples from the far side of the moon, which always faces away from Earth. Now, two new studies examining those samples — which include the oldest evidence to date of lunar volcanism — paint a deeper picture of the moon's geological history.
Researchers said on Friday that soil brought back from the Chang'e-6 landing site contains fragments of volcanic rock – basalt – formed between 4.2 billion years ago and 2.8 billion years ago. This points to a period of volcanic eruptions at least 1.4 billion years ago on the far side during the first half of the moon's history, when it was a much more dynamic landscape than it is today.
Volcanic eruptions on the moon, Earth and other planetary bodies involve the eruption of molten rock from the mantle – the layer below the outer crust – to the surface. The South Pole-Aitken Basin, an impact crater, is a very thin crustal area on the moon, useful for finding evidence of volcanism.
The Chang'e-6 probe used a scoop and drill to find about 1,935 grams of soil, containing more than 100 pieces of basalt. It then brought things back to Earth, and settled in the Chinese region of Inner Mongolia.
“The Chang'e-6 samples provide a unique opportunity to study the side volcano,” said lunar scientist Qiu-Li Li of the Chinese Academy of Sciences, who helped lead the study in the journal Nature, one of two published on Friday. findings, another in the journal Science.
The researchers used radioisotope dating to determine the age of various pieces of volcanic rock found in the samples.
A place that has exploded over the years
We've known for a long time that the moon used to be a very explosive place – samples of lunar basalt were previously found on the near side of the moon, which always faces the Earth, during the US Apollo, Soviet Luna and Chinese Chang'e-5. on a trip.
This showed that the eruption on the near side of the volcano occurred as early as 4 billion years ago and continued for at least 2 billion years, Li said.
The video, provided by China Central Television, shows the Chang'e-6 probe as it touches down on Earth, returning the first samples collected from the far side of the moon.
“The exact time and length of the volcanic month is not easy and probably varies from place to place. Some small volcanic eruptions may have happened nearby about 120 million years ago as recorded by volcanic glass beads from Chang'e-5 samples” collected in 2020, said Li.
While previous studies, including data from NASA's Lunar Reconnaissance Orbiter, have suggested the far side may have had a volcanic past, this is the first time samples have been able to confirm that. Evidence of volcanism as recently as 2.8 billion years ago on the far side is unprecedented on the near side.
Different volcanic sources
The researchers also found that the 4.2-billion-year-old basalt is different in composition from the 2.8-billion-year-old basalt, meaning it comes from different sources of molten rock — magma — in the mantle, Li said.
The Chang'e-6 samples, Li said, also differ in composition compared to previously collected lunar samples from the near side.
There is no evidence of active volcanism on the moon, unlike other places in the solar system such as Venus and Earth.
“The end of volcanism on the moon is due to the depletion of internal heat sources over time. Initially, the volcanism of the moon was driven by the decay of radioactive elements and residual heat from its formation, which created enough internal energy to continue melting the mantle and, as a result, volcanic eruptions ,” said Li.
As heat sources dwindled, the moon's mantle cooled, he added — a process accelerated by the moon's small size.
The moon's diameter of about 3,475 kilometers is a little more than a quarter of the diameter of the earth.
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