New results from China’s Chang’e 5 lunar samples returned to Earth provide evidence for active volcanoes on the Moon as recently as 120 million years ago. Previously, scientists had thought that any activity with magma (molten rock) rising to the Moon’s surface ended billions of years ago.
The work is published in a paper by Bi-Wen Wang and colleagues from the Chinese Academy of Sciences in the Sept. 6 issue of Science. In a commentary in the same issue, Professor Qing-Zhu Yin, UC Davis Department of Earth and Planetary Sciences and Yuri Amelin, Korea Basic Science Institute, write that the new work will add to ongoing debates about thermal evolution and cooling of planets.
Wang and colleagues sorted a needle from a haystack to make their observations, Amelin and Yin said.
When the Earth and Moon formed about four and a half billion years ago, they were balls of molten rock which cooled to form a solid crust. Volcanic activity brought magma to the surface where it flowed out to form the “seas” or “maria” that we can see on the Earth-facing side of the Moon. Based on results from the Apollo and the Russian Luna missions in the 1970s, this activity ended by about 3.1 billion years ago, meaning that the rocks on the surface of the Moon are all at least this old.
However, more recent data, including by China’s Chang’e expeditions, suggest that there are younger rocks on the Moon’s surface, just under 2 billion years old.
Moon goddess
China’s Chang’e 5 lunar explorer was launched in November 2020 and landed on the Moon in December. It was designed to collect lunar samples and return them to Earth. Like the other probes in China’s lunar exploration program, it is named after the Moon goddess of Chinese mythology.
Wang and colleagues combed lunar soil samples returned by the Chang’e 5 mission for evidence of volcanic activity in the form of microscopic glass beads. These glasses solidify from molten rock and contain mineral traces and isotopes that give evidence of their age and origin.
Unfortunately, there is more than one way to get melted rock on the Moon’s surface. Lacking atmosphere, the Moon is constantly bombarded by meteorites, many of which melt with the energy of impact.
Wang and colleagues hypothesized that beads formed from a volcanic eruption – which brings material from deep in the Moon – would have a different chemical signature to beads formed from meteorites that melted on impact.
After sorting through over 3,000 beads, they identified three that were distinct from the rest based on their chemical composition and isotopes, which were consistent with volcanic origin. They were able to date these as coming from eruptions about 120 million years ago, during the Cretaceous period on Earth.
“The effort that Wang et al. put into finding the volcanic “needle” in the impact-generated “haystack” has paid off,” Amelin and Yin wrote.
The beads were not necessarily erupted near where they were found. As well as bringing rocks to the Moon, meteorite impacts scatter debris widely across the lunar surface. Wang et al argued that through this process, they could and have sampled glass beads erupted from fire fountains elsewhere on the Moon and recovered by Chang’e-5.
“There are many features on the Moon suspected to be very young based on remote sensing data,” Yin said.” The approach taken by Wang et al is the next best thing to a spacecraft visit to those specific young features.”
Clearly, very young volcanos might not be the last word on planetary evolution, Yin said.
“At this point, we simply do not know how a small planet could still maintain active volcanism without cooling off completely. With manned missions to the Moon coming up (both US and China), ground truth is surely going to surprise us even more,” he said.