Lunar samples reveal volcanic activity as late as 2 billion years ago

(CN) — The mysteries of the moon have a new, volcanic layer.

In 2021, China’s Chang’E-5 mission returned to Earth with lunar samples. As scientists from the Institute of Geology and Geophysics of the Chinese Academy of Sciences (IGGCAS) studied the samples, they noted that prior lunar missions such as Apollo and Luna recovered samples older than 3 billion years. As such, scientists initially believed that the moon was geologically dead since then, according to a study published Friday in Science Advances.

Chang’E-5’s samples challenged that theory about Earth’s only natural satellite.

Led by Professor Yi Chen, the researchers reported that the samples contained signs of volcanic activity that was only 2 billion years old, the youngest lunar volcanic rocks to date. Upon further study, the researchers found that mantle melting-point depression caused by the presence of fusible, easily melted components could generate young lunar volcanism.

This finding prompted the question of how this happened.

The scientists first hypothesized that either elevated water content or heat-producing elements in the lunar interior drove volcanism in the late state of the moon’s life. However, Chang’E-5’s samples disproved these theories, scientists revealed in two articles published in the journal Nature in 2021.

Dr. Bin Su, first author of the study, believes the location provides one explanation.

“The selected landing site of the Chang’E-5 targeted potentially some of the youngest lunar volcanic regions,” Su said in an email. He said the researchers used crater counting chronology, an estimate of the age of a planet’s surface by the various sizes of impact craters, to predict that the lava flows at the Chang’E-5 landing site are much younger than the basalts collected by the Apollo and Luna missions.

To further explain what caused the young volcanism, the team tested the Chang’E-5 and Apollo basalts against each other.

Su said that because the basalts underwent composition change during magma ascension and eruption, the team used petrological modeling to deduce their primary magmas’ original compositions and estimate the temperature and pressure that formed them.

After comparing 27 precious Chang'E-5 basalt clasts to Apollo basalts, the researchers found the Chang’E-5 source magma contained greater calcium oxide and titanium dioxide content than the Apollo magmas. Per the study, the late-stage lunar magma ocean cumulates are rich in calcium-titanium and more easily melt than early cumulates. Because of this, the fusible components possibly joined the lunar interior through gravitationally driven mantle overturn.

Also, the researchers found that the Chang’E-5 magma was 176 degrees Fahrenheit cooler than older Apollo magmas. This means that the lunar mantle experience sustained, slow cooling to that temperature between 3 billion years to 2 billion years ago, and that the fusible components joining the lunar interior reduced the mantle melting temperature and triggered the young lunar volcanism.

All this new information presents the first viable mechanism to account for young volcanism on the moon, and what researchers hope will help planetary scientists better understand its thermal and magmatic evolution.

However, Chen noted this study highlights how much we currently do not know.

“Even after years of exploration, the moon remains a largely mysterious world. It is our nearest neighbor in space and can be responsible for many aspects of the Earth today (e.g., tide, climate, and magnetic field). To better understand our Earth, we call for more attention to the moon’s origin and evolution,” Chen said in an email.

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