Chinese lunar mission test catch includes exotic volcanic rocks

Samples returned from the Moon by the Chinese mission have been found to contain exotic types of igneous rock associated with material ejected from powerful impacts.

Exotic “clasts” have been found in samples of lunar regolith (dust and dirt) collected by the Chang’e 5 mission around Rümker Mountain, in the lunar region’s northern Oceanus Procellarum (“Ocean of Storms”).

Zeng Xiaojia, Li Xiongyao and Liu Jianzhong of the Institute of Geochemistry of the Chinese Academy of Sciences (IGCAS) found the debris among 3,000 samples and 3.82 pounds (1.73 kg) of lunar regolith returned to Earth by a December 2020 mission.

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The discovery could provide important information about the diversity of rocks on the lunar surface and the processes that create its regolith, the researchers say. The finds also point to a hitherto unknown variety of magma in the lunar crust.

The seven exotic fragments identified by the team include a high-titanium “vitophyric fragment” that consists of large crystals known as phenocrysts embedded in a glassy mass known to form here on Earth as a result of volcanic activity. Lunar regolith samples also contain olivine-pyroxenite, a highly shaken igneous rock called magnesian anorthosite, and a ball of pyroclastic glass.

These materials are also associated with violent eruptions and cosmic impacts. They were most likely brought to the Chang’e 5 research area from other lunar regions at a distance of 31 to 249 miles (50 to 400 kilometers).

The team also compared Chang’e 5 regolith samples with lunar material brought to Earth by NASA’s Apollo missions between 1969 and 1972. Researchers have found three exotic igneous fragments in the Chang’e 5 regolith that show unusual formational and compositional features.

In particular, the titanium-rich vitrophyric fragment has a mineralogy unique to lunar basalts, meaning that it likely represents a previously unknown form of this igneous rock type. Magnesian anorthosite clasts are a type of rock not found in the Apollo samples. Its presence in the Chang’e 5 collection may indicate that magnesian anorthosite is an important component of the lunar crust on the Earth-facing side of the Moon.

The pyroclastic glass ball is perhaps the most interesting of the recently analyzed samples. According to members of the research team, the bead indicates a volcanic eruption on the Moon that was different in composition from normal lunar volcanic eruptions that were common on the Moon between 4.2 and 3 billion years ago.

The new study represents the first time exotic igneous rock types have been found in samples from this relatively young (two billion year old) lunar basaltic region. The data obtained can help to better model the formation of regolith in the Mons-Rümker region.

The discovery of exotic igneous debris in the samples suggests that there are still unknown geological regions on the Moon, which could affect the planning of future lunar missions.

The study was published last month in the journal Nature Astronomy. (will open in a new tab). (will open in a new tab)

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