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The historic Chandrayaan-3 mission, which made India the fourth country to land on the moon a year ago on Friday, has yielded new evidence supporting a theory about the moon’s early history.
When the mission landed in the moon’s southern high latitudes, near the lunar south pole, it deployed a small six-wheeled rover called Pragyan, which means wisdom in Sanskrit. The rover was equipped with scientific instruments that allowed it to analyze particles in the lunar soil and measure the elements there.
Pragyan took 23 measurements as it rolled over a 338-foot (103-meter) area of the lunar surface, located 164 feet (50 meters) from Chandrayaan-3’s landing site, over a period of about 10 days. The rover’s data mark the first measurements of elements in lunar soil near the south polar region.
The rover found a relatively uniform composition consisting largely of a rock called ferroanorthosite, a composition similar to samples taken from the moon’s equatorial region during the Apollo 16 mission in 1972.
The findings were published Wednesday in the journal Nature.
Lunar samples help scientists solve mysteries about how the Moon evolved over time, including how the Moon formed during the chaotic early days of the solar system.
The presence of similar rocks in several places on the moon supports the decades-old hypothesis that the moon was once covered by an ancient ocean of magma, the study authors said.
An ancient magma ocean
There are many theories about how the moon formed, but scientists largely agree that about 4.5 billion years ago, a Mars-sized object or series of objects crashed into Earth, sending enough molten debris into space to form the moon.
The first lunar samples collected during the Apollo 11 mission in 1969 led researchers to theorize that the Moon was once a molten ball of magma.
The 842 pounds (382 kilograms) of moon rocks and soil brought back to Earth by the Apollo missions in the late 1960s and early 1970s disproved ideas that the moon was a celestial body trapped in Earth’s gravity or that the moon formed from the same debris as Earth. The rock samples indicated that the moon formed about 60 million years after the solar system formed, NASA said.
The magma ocean, likely hundreds to thousands of kilometers deep, lasted for about 100 million years, the space agency said. As the magma ocean cooled, crystals formed in it.
Some rocks and minerals such as ferroan anorthosite rose upward to form the lunar crust and highlands, while other, denser magnesium-rich minerals such as olivine sank deep below the surface into the mantle, said Noah Petro, NASA project scientist for both the Lunar Reconnaissance Orbiter and Artemis III. Petro was not involved in the new study.
While the lunar crust has an average thickness of about 50 kilometers, the lunar mantle beneath it is about 1,350 kilometers thick.
All the minerals and rocks on the moon tell a story about the moon’s history, Petro said.
When the Pragyan rover investigated the chemical composition of the lunar soil, it found a mixture of ferroanorthosite and other types of rocks, including minerals such as olivine.
Chandrayaan-3’s landing site, called Shiv Shakti Point, was located about 350 kilometers from the edge of the South Pole-Aitken Basin, considered the oldest crater on the moon.
The research team is confident that an asteroid impact created the basin about 4.2 to 4.3 billion years ago, exposing magnesium-rich minerals such as olivine that were then mixed with the lunar soil, said Santosh Vadawale, lead author of the study and a professor at the Physical Research Laboratory in Ahmedabad, India.
The researchers continue to investigate the presence of these minerals, which likely came from the moon’s mantle, to provide more context for the moon’s origins and evolution, he said.
Enduring Moon Mysteries
The mission proves why sending spacecraft to different regions of the moon is critical to understanding the moon’s history, Vadawale said.
“All previous successful lunar landings were confined to the equatorial to mid-latitudes,” he said. “Chandrayaan-3 is the first mission to successfully land in the lunar polar regions and perform in situ analyses. These new measurements in previously unexplored areas further strengthen the confidence in the (lunar magma ocean) hypothesis.”
Next, India’s lunar exploration program aims to explore the permanently shadowed regions of the lunar poles and return samples for detailed analysis in laboratories on Earth, Vadawale said.
While erosion and the movement of tectonic plates have erased evidence of how Earth formed, the moon, aside from impact craters, has remained largely unchanged, Petro said.
“Every time we land on the lunar surface, that understanding is anchored to a specific spot, a specific location on the surface, which is really useful for testing all the models and hypotheses that we have,” he said. “That magma ocean hypothesis drives so much of what we think about the moon, especially early in its history. The results from the rover on the Chandrayaan-3 mission add another surface data point.”
Each mission not only adds a new piece to the puzzle of understanding the moon, but also provides insight into how Earth and other rocky planets like Mars formed. Scientists’ understanding of how the moon formed drives models of how all planets form and change, including planets outside our solar system, Petro said.
And with more missions to the lunar surface planned, it’s a gift that keeps on giving, especially with the prospect of collecting samples from different regions, including the far side of the moon and the poles.
“Every time we get a new piece of data,” Petro said, “it’s an additional decoration of that gift.”
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