What do the samples returned back by the Chinese spacecraft reveal about the Moon?

 On December 16, 2020, China’s Chang’e-5 lunar mission delivered to Earth nearly 2 kg of rocky fragments and dust from the Moon. At the ongoing Europlanet Science Congress (EPSC) 2021 virtual meeting, Yuqi Qian, a PhD student at the China University of Geosciences, presented early-stage findings that use geological mapping to link ‘exotic’ fragments in the collected samples to features near the landing site, the Europlanet Society said in a press release.

Chang'e-5 landed on a part of the Moon (the 'far side') that had never been examined by American or Soviet missions nearly 50 years ago, bringing back fragments of the youngest lunar rocks ever brought back for study in Earth laboratories. The rocks are also not the same as those found decades before.

THE FINDING:

According to the Europlanet Society, Qian's analysis revealed that 90 percent of Chang'e-5's materials came from the landing site and its immediate surroundings, which are composed of "mare basalts," a type of rock. During earlier lava outbreaks, these volcanic rocks may be observed as darker grey patches that spilled across most of the Moon's nearside. However, 10% of the pieces had chemical compositions that are significantly different and referred to as "strange."

WHY IT MATTERS:

The different 10% fragments could have records of other sections of the lunar surface, as well as insights about the types of space objects that have collided with the Moon's surface. Qian and colleagues from Brown University and the University of Münster investigated the sources of glassy beads that have rapidly cooled. These glassy drops were discovered near the extinct volcanic vents ‘Rima Mairan' and ‘Rima Sharp.' According to the press release, these shards could reveal information on past episodes of explosive, fountain-like volcanic activity on the Moon.

The team has also looked into possible impact-related fragment sources. The short geological age of the rocks at the landing location narrows the search, as only craters younger than 2 billion years can be responsible, which are uncommon on the Earth-facing side of the Moon. Aristarchus, Kepler, Copernicus, Harding, and Harpalus are among the craters whose possible contributions have been modelled. According to the release, Qian's findings reveal that Harpalus is a substantial source of numerous unusual fragments among Chang'e-5's sample haul, and these pieces of rock could give a solution to resolve the crater's age uncertainty.