First lunar samples in over 45 years offer new clues to the moon's volcanic history
Last December, China's ambitious lunar sampling mission returned to Earth with the first lunar samples since NASA's Apollo and Russia's Luna missions, which ended in 1976. The first fresh samples in 45 years have now been analyzed — and they hold answers to previous questions about the moon, while also creating new ones, according to research published Tuesday in the journal Nature.
The Chang'E-5 mission, named after the goddess of the moon from traditional Chinese mythology, brought back almost 4 pounds of lunar soil and rock from a previously unvisited piece of basalt. The basalt, a type of rock made from solidified lava flow, was thought to hold evidence of when volcanic activity occurred on the Moon's surface.
The research team used radiometric dating on 47 basalt fragments — the largest, about the thickness of "10 pages stacked together" and the smallest, only the size of a dust particle — and learned they were around 2 billion years old.
Scientists were surprised to learn that the samples were 800 to 900 million years younger than the Apollo and Luna samples indicated.
Nevertheless, "This is the youngest crystallization age ever reported for lunar basaltic rocks by radiometric measurement, extending the… ages of lunar basalt by 800 to 900 million years," researcher Li Chunlai of the National Astronomical Observatories of the Chinese Academy of Sciences said in a press release accompanying the study. "This study provides the first conclusive evidence that magmatic activity on the Moon persisted until at least two billion years ago."
The new samples also helped refine a method of determining the age of a planet, known as crater-counting chronology. While the Apollo and Luna samples "provided an initial database for ages ranging from 4 to 3.1 billion years ago, as well as those younger than one billion years ago," the new Chang'E samples provides data in the middle, "fulfilling the long-sought-after goal to bridge the unanchored middle portion of the lunar crater-counting chronology," Li said.
But the samples also created new mysteries. The Apollo and Luna samples were composed of KREEP, a mixture of potassium, rare earth elements and phosphorus — but the Chang'E samples were made of a different kind of magma.
"According to the previous theory, the KREEP-like components would provide heat to sustain the longevity of young magma. However, if this is not the case - as these results suggest - we should rethink the mechanisms underlying the longevity of the younger lunar magmatic activity," Li said.
The scientists said the discovery changes how they think about the "thermal and chemical evolution" of the moon. The research team plans to continue to analyze the samples, and to hopefully shine a light on how — and why — lunar volcanic activity changed between the Apollo and Luna samples and the Chang'E samples.
