Chang’e-5 Returned an Exotic Collection of Moon Rocks

Scientists are now studying samples from the Moon returned by China's Change-5 mission in Dec 2020. A group of researchers presented their first findings last week at the Europlanet Science Congress.
The Change-5 samples include both local and exotic materials. Yuqi Qian is a PhD student at China University of Geosciences. He presented his findings at the EPSC virtual meeting.

Panorama view taken from China's Change-5 probe. It shows the lunar terrain and one of the landing legs. (CNSA/CLEP Photo).

Change-5 landed in the Oceanus Procellarum or Ocean of Storms on the Moon's near side. This is the central, western part of the Moon, from Earth's vantage point. The area it landed was not explored by either the Soviet Luna or NASA Apollo missions. It was almost 50 years ago. This is also the oldest lunar surface, at around 2 billion years of age. These samples are therefore different from those that were returned in the 1960s or 70s.

Qian stated that the samples are extremely diverse because we know for a long time that the formation lunar surface is a complex process. This includes solar wind implantation, micrometeorite impact, and condensation.

Young mare basalts and local impact ejecta are the local materials that make up around 90 percent of the returned samples. Exotic materials, which are materials that are not native to the area, account for about 10% of the Change-5 samples. They include meteoritical materials and distant impact ejecta.

The Change-5 lunar landing craft retrieved approximately 1.7 kg (3.81 lbs) of samples from Moon. It used a drill for subsurface samples and a robotic arm to collect surface samples. On December 16, 2020, the Change-5 sample return capsule arrived in China's Inner Mongolia region. It successfully completed a 23-day journey that brought back the first lunar rock since 1976.

Qian and his colleagues from Brown University, the University of Mnster, have examined the possible sources of the glass beads and traced the rapidly cooling glassy droplets to the now-extinct volcanic vents known Rima Mairan (located approximately 230 km southeast and northeast of Change-5 landing site). These fragments may provide insight into past episodes of active, fountain-like volcanic activity.

The team also examined the possible sources of fragments from impact. The landing site's young geological age limits the possibilities of finding responsible craters. These craters must be less than 2 billion years old, which is rare on the lunar near-side.

Image showing Change-5 landing site location (43.06N 51.92W), adjacent Moon regions, and impact craters which were investigated as potential sources of exotic lunar fragments. Credit: Qian et al. 2021

The team modelled what craters might have produced the exotic materials. They found that some materials could have been ejected as far as 1,300km from the Change-5 landing area. The team discovered that Harpalus is located further north of Change-5s site and was a significant contributor to many exotic fragments amongst the samples. They also found craters in the southeast (Aristarchus Kepler and Copernicus) and northwest (Harding).

Modeling and reviewing work from other teams have linked other unusual pieces of rock to silica-rich domes or highland terrains around the landing site.

Qian stated that all of the Change-5 samples returned can be used to answer further scientific questions. These questions will be addressed to deepen our knowledge of the Moon's history and prepare us for future lunar exploration.

The team's findings can be found here.

Caption: Image of Change-5 sample CE5C0400 taken from the Moon's surface. The Change-5 fraction of lunar materials that was returned to Earth weighs in at nearly 35 grams. It was taken by a robotic arm. Credit: CNSA (China National Space Administration), CLEP (China Lunar Exploration Program), / GRAS [Ground Research Application System].