Lunar soil sample contains minerals that promise new discoveries about Moon

The Moon acquired its distinctive appearance due to collisions with celestial bodies that created impact craters on its surface. However, these collisions leave more than just craters; they also exert significant pressure and elevated temperatures, altering the mineral composition and structure of the lunar surface. Analyzing these changes helps unveil many aspects of Earth's satellite's past.

Recently, 1.73 kilograms of regolith were delivered to Earth, collected during the Chinese Chang'e-5 mission. The area from which the samples were taken is known as Oceanus Procellarum. One of the samples contained a new mineral, Changesite-(Y), and an intriguing combination of silica minerals (SiO2, silicon dioxide (IV)).

Scientists from the Chinese Academy of Sciences, in their work titled "Matter and Radiation in Extreme Conditions," compared the composition of the sample with other lunar and Martian regolith samples.

High-speed collisions with asteroids and comets induce shock metamorphism in lunar rocks. Changes in temperature and pressure occur rapidly, leading to the formation of polymorphic forms of silica, such as stishovite and coesite. While chemically identical to quartz, they possess a distinct crystalline structure.

One scientist, Wei Du, noted that despite the abundance of impact craters on the Moon's surface, high-pressure minerals are rarely found in samples. He explained that this may be due to the instability of such minerals at high temperatures. Therefore, those formed during collisions might have undergone reverse transformations.

Nevertheless, a silica fragment from the Chang'e-5 sample contains both stishovite and coesite, which theoretically can only exist at much higher pressures than those experienced by the sample. Researchers suggest that coesite formed from α-cristobalite during compression, and then part of the sample transformed into stishovite due to increased temperature.

Additionally, in the Chang'e-5 sample, scientists identified the mineral Changesite-(Y), a phosphate characterized by colorless transparent crystals. Researchers assessed the impact parameters that led to the sample's formation: peak pressure ranged from 11 to 40 GPa, and the duration of impact varied from 0.1 to 1.0 seconds. Researchers also estimated the sizes of the resulting craters using shock wave models, approximately ranging from 3 to 32 kilometers in width, depending on the impact angle.

Scientists noted that regolith ejections associated with the sample mostly originate from four impact craters, with Aristarchus being the youngest. Studying the samples allows the conclusion that the silica fragment containing coesite and stishovite possibly formed as a result of a collision, leading to the formation of the Aristarchus crater.

The findings of this research contribute to understanding how the Moon's surface forms and how collisions influence its mineral composition.