Exotic Clasts in Chang’e-5 Samples Indicate Previously Unexplored Terranes on the Moon

Credit: CNSA/CLEP.

In December 2020, the Chinese National Space Administration (CNSA) returned nearly two kilograms of material from the Mons Rümker region (part of the Oceanus Procellarum) in the northern latitudes of the lunar nearside as part of the Chang’e-5 mission. Radiometric age dating of these samples has revealed that they crystallized approximately two billion years (2.0 Ga) ago, making them the youngest sampled units of lunar basalt studied with radiometric dating.

Modeling suggests that diverse materials from multiple source regions would have been transported to the Chang’e-5 sampling region by processes such as meteorite impacts and volcanic activity. Numerical models predict that anywhere from 20-40% of the material sampled could be “exotic” material from a variety of sources. These exotic components could represent samples from yet unexplored regions of the Moon and provide the perfect opportunity to investigate the lithological diversity of the sample collection region and surrounding areas.

Xiaojia Zeng and colleagues from the Chinese Academy of Sciences studied more than 3,000 of Chang’e-5’s regolith particles and identified seven exotic igneous clasts that show distinct petrological and mineralogical characteristics. The authors surmise that these fragments were ejected from other regions on the Moon from 50-400 kilometers away. They also identified a compositionally unique glass bead that is chemically evolved (low Mg, high Fe contents) relative to previously studied lunar glass beads returned by the Apollo missions. This would suggest the existence of previously unrecognized, evolved volcanic eruptions on the Moon, adding to the increasing variety seen among lunar samples. The authors note that the amount of exotic material found in the Chang’e-5 samples is significantly lower than was predicted by models (about 0.2% compared with 20-40%), suggesting that current methods for modeling impact ejecta may need to be revised for the younger terranes on the Moon. READ MORE