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The mission to the Chinese moon Chang’e 5 has discovered an exotic type of igneous rock with an extraordinary impact material. Photo/NASA/Space
Exotic clastic rocks have been found in lunar regolith samples collected by the Chang’e 5 mission in the vicinity of Mons Rümker, in the northern part of the moon’s Oceanus Procellarum (Sea of Storms) region. The results also demonstrate a hitherto unknown diversity of magma across the lunar crust.
Zeng Xiaojia, Li Xiongyao and Liu Jianzhong of the Institute of Geochemistry of the Chinese Academy of Sciences (IGCAS) found fragments among 3,000 samples and 1.73 kilograms of lunar regolith returned to Earth by the mission in December 2020.
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“This discovery may provide important insights into the diversity of rocks on the lunar surface and the processes that create their regolith,” the researchers said.
The seven exotic classes identified by the team include high-titanium vitrofic fragments, which consist of large crystals known as phenocrysts. This material is embedded in glass masses known to have formed on Earth through volcanic activity.
Also present in lunar regolith samples are olivine-pyroxenite, an igneous rock called magnesian anorthosite, and pyroclastic glass beads. These materials are also associated with catastrophic eruptions and cosmic impacts.
It is likely that this material has been found in other lunar areas up to 50-400 kilometers. The team also compared the Chang’e 5 regolith samples with lunar material brought back to Earth by NASA’s Apollo missions between 1969 and 1972.
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Researchers have found three exotic igneous clasts in the Chang’e 5 regolith that exhibit unusual formation and compositional characteristics. In particular, the high-titanium vitrofic fragments have a mineralogy unique to lunar basalt, meaning they are likely previously unknown forms of this igneous rock type.
The magnesian anorthosite class is a rock type not found in the Apollo samples. Its presence in the Chang’e 5 collection may indicate that magnesium anorthosite is a major component of the lunar crust on the Earth-facing side of the moon.
The pyroclastic glass bead is perhaps the most interesting of the samples just analysed. The heel implies volcanic eruptions on the moon that were of a different composition from normal volcanic eruptions that were common on the moon between 4.2 and 3 billion years ago, study team members said.
The new study represents the first time that an exotic igneous rock type has been found in samples from the relatively young (two billion year old) basaltic region of the moon. These results may help to better model the formation of regolith in the Mons Rümker region.
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The discovery of an exotic frozen class in the sample indicates that there are still unknown geological regions on the moon, something that could affect the planning of future lunar missions.
(wib)
