2024-02-06 16:23:10
MADRID, 6 Feb. (EUROPA PRESS) –
In the magazine ‘Matter and Radiation at Extremes’ Researchers from the Chinese Academy of Sciences reveal new clues about the origin of the Moon.
The data comes from China’s Chang’e-5 — the first lunar sample return mission since the Soviet Union’s Lunik program in 1976 — which brought back 1.73 kilograms of regolith from the Oceanus Procellarum, a plain called thus due to its large size. The sample landed in late 2020 and included a new mineral, Changesite-(Y), as well as a disconcerting combination of silica minerals.
In this new research, the researchers have analyzed the composition of the CE-5 material with other samples of lunar and Martian regolith. Thanks to this analysis, they examined the possible causes and origins of the unique composition of the lunar sample. It is worth contextualizing that the Earth’s moon achieved its Swiss cheese appearance from celestial objects that collided with its surface, forming impact craters.
But the craters were not the only thing left behind. The intense pressure and temperature of such a collision also impacts the rocks and dust that cover the lunar surface, known as regolith, altering its composition and mineral structure.
“Although the lunar surface is covered by tens of thousands of impact craters, high-pressure minerals are rare in lunar samples,” says author Wei Du. “One of the possible explanations for this is that most high-pressure minerals are unstable at high temperatures. Therefore, those that formed during the impact could have experienced a retrograde process.”
However, a silica fragment in sample CE-5 contains both stishovite and seifertite, minerals that theoretically only coexist at much higher pressures than the sample apparently experienced. The authors determined that seifertite exists as a phase between stishovite and a third silica polymorph, alpha-cristobalite, also present in the sample.
“In other words, seifertite could form from alpha-cristobalite during the compression process, and part of the sample could be transformed into stishovite during the subsequent temperature increase process“, reflects Du.
This mission also returned a new lunar mineral, Changesite-(Y), a phosphate mineral characterized by transparent, colorless columnar crystals. The researchers estimated the maximum pressure (11-40 GPa) and impact duration (0.1-1.0 seconds) 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. Remote observations show that distant ejecta in the CE-5 regolith come mainly from four impact craters, and Aristarchus crater is the youngest of the four distant craters.
Because seifertite and stishovite are easily altered by thermal metamorphism, they inferred that The silica fragment probably originated from the collision that formed the Aristarchus crater. This sample return mission demonstrated the power of modern analysis and how it can help uncover the history of celestial bodies.
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