Old and new minerals identified in lunar samples brought back by China’s Chang’e-5 mission are helping scientists better understand the history of the Moon: now, specialists have discovered more properties of the sixth new lunar mineral, called Changesite-(Y). Furthermore, other compounds found, seifertite and stishovite, can only coexist at much higher pressures than the sample appears to have witnessed: therefore, their existence indicates a “baffling combination” of materials, which scientists have not yet discovered. managed to explain.
Researchers from the Chinese Academy of Sciences examined in a new study, recently published in the journal Matter and Radiation at Extremes, the possible causes and origins of the unique composition of the lunar sample returned by the mission. Chang’e-5 in 2020: the analysis focuses on the properties of the new mineral Changesite-(Y), discovered in 2022, and on the presence of an anomalous combination of materials, which does not match the pressure conditions existing in the context of the sample.
A bombing that left its traces
The Moon It achieved its characteristic image from celestial objects that collided with its surface, forming impact craters. However, these craters are not the only vestige of the “bombardment” to which our only natural satellite was subjected: the intense pressure and temperature of the collisions also modified the rocks and dust that cover the lunar surface, known as regolith, altering its mineral composition and structure. Analysis of these minerals provides clues to the Moon’s past, which scientists are trying to unravel.
According to one Press release From AIP Publishing, China’s Chang’e-5 probe, the first lunar sample return probe since the former Soviet Union’s Luna 24 mission in 1976, delivered 1.73 kilograms of regolith from the region of Oceanus Procellarum (Ocean of Storms), an extensive lunar sea composed of basaltic outcrops. The sample arrived on Earth around the end of 2020 and included a new mineral, Changesite-(Y)as well as a disconcerting combination of silica minerals.
A strange combination
After comparing the chemical composition of the material returned by the Chinese mission with other samples of lunar and martian regoliththe scientists verified that silica polymorphs such as stishovite and seifertite, which are chemically identical to quartz but have different crystalline structures, should not have been able to coexist under the pressure conditions prevailing in the context of the sample.
If we add to this the strange characteristics of the new mineral Changesite-(Y), researchers speak of a “baffling combination” of minerals, which forces them to redouble their efforts to try to understand their origin and nature. In addition, the specialists estimated the maximum pressure and duration of the impact of the collision that shaped the sample. Combining that information with shock wave models, they estimated that the resulting crater would be between 3 and 32 kilometers wide, depending on the angle of impact.
Analyzing training conditions
According to a article published on Space.com, Changesite-(Y) must have formed after one of these impacts: a previous analysis pegged the age of the lunar rocks returned by Chang’e-5 at 1.97 billion years. As for seifertite and stishovite, scientists believe that these two minerals were probably deposited by the collision that formed the Aristarchus crater, the youngest in the Oceanus Procellarum region. However, their joint presence under these conditions is anomalous.
Although seifertite is known to transform into stishovite during high-pressure aftershocks in these types of impacts, there is still much to learn about these minerals in the future. Moon. “The lunar surface is covered by tens of thousands of impact craters, but high-pressure minerals are rare in lunar samples. One possible explanation for this is that most of the high pressure minerals are unstable at high temperatures,” concluded scientist Wei Du, one of the authors of the new study, in the previously cited statement.
High-pressure minerals and new lunar mineral changesite-(Y) in Chang’e-5 regolith. Jing Yang and Wei Du. Matter and Radiation at Extremes (2024). DOI:https://doi.org/10.1063/5.0148784