By James Gamble via SWNS
The first lunar lander mission in 50 years has returned with dust that offers clues to how moon craters formed.
Never-before-seen lunar material returned by China’s Chang’e-5 mission could shed light on the origin of craters that give the moon its Swiss-cheese-like appearance.
Researchers discovered that celestial objects crashed into the moon to form these craters, with the intense pressure also impacting the rocks and dust covering its surface.
Using this newly collected moon dust, scientists were able to predict which craters they derive from.
The moon arrived at its Swiss cheese appearance after continual crashes into its surface, forming huge impact craters.
But the craters weren’t all that was left behind.
The intense pressure and temperature of these lunar collisions also impacted the rocks and dust covering the moon’s surface, known as regolith, altering its mineral composition and structure.
Analysis of the resulting materials, published in the journal Matter and Radiation at Extremes, affords scientists with an insight into the moon’s history.
China’s Chang’e-5 (CE-5) – the first lunar sample return mission since the Soviet Union’s Luna 24 in 1976 – recently returned to Earth with 1.73 kilograms of regolith from the Oceanus Procellarum, a lunar plane on the western edge of the near side of the moon, named for its vast size.
The sample landed with CE-5 in late 2020 with a new mineral, Changesite-(Y), as well as a perplexing combination of silica minerals.
Researchers from the Chinese Academy of Sciences compared CE-5’s material composition to other lunar and Martian regolith samples and examined potential causes and origins for the lunar sample’s unique makeup.
Asteroids and comets are known to collide with the moon at extreme velocities, causing impact metamorphism in the lunar rocks.
This temperature and pressure change occurs rapidly and has distinctive features, including the formation of silica polymorphs like stishovite and seifertite, which are chemically identical to quartz but have different crystalline structures.
Study lead author Dr. Wei Du said: “Although the lunar surface is covered by tens of thousands of impact craters, high-pressure minerals are uncommon in lunar samples.
“One of the possible explanations for this is that most high-pressure minerals are unstable at high temperatures.
“Therefore, those formed during impact could have experienced a retrograde process.”
However, a silica fragment in the CE-5 sample was found by the researchers to contain both stishovite and seifertite; minerals that theoretically only coexist at much higher pressures than the sample ostensibly experienced.
The researchers determined that seifertite exists as the phase between stishovite and a third silica polymorph – α-cristobalite – which was also present in the sample.
“In other words, seifertite could form from α-cristobalite during the compressing process, and some of the sample transformed to stishovite during the subsequent temperature-increasing process,” Dr. Du said.
The lunar mission also returned a new mineral called Changesite-(Y): a phosphate mineral characterized by colorless, transparent columnar crystals.
The researchers estimated the peak pressure (11-40 gigapascals) and impact duration (0.1-1.0 second) of the collision that shaped the sample taken by the research team’s lunar lander.
Combining this information with shock wave models, they estimated the resulting crater to be anywhere between three and 32 kilometers wide, depending on the angle
of the impact.
Remote observations show that distant ejecta in CE-5 regolith mainly come from four impact craters, with the Aristarchus crater the youngest among the four distant craters.
Because seifertite and stishovite are easily disturbed by thermal metamorphism, the researchers concluded that the silica fragment likely originated from the collision that formed the Aristarchus crater.
They hailed their complicated sample return mission as demonstrating the power of modern analysis and how it can help uncover the history of celestial bodies.
