For decades, debate has raged over whether the moon ever had a strong magnetic field or whether it was always weak. Now, a new analysis of Apollo-era moon rocks suggests that the moon’s magnetic field may be mostly weak despite brief bursts of strong activity, potentially solving the mystery for good.
The study, published Thursday (February 26) in the journal Nature Geoscience, shows that the moon’s magnetic field briefly strengthened early in its history, about 3.5 billion to 4 billion years ago, but that it remained weak for most of the moon’s 4.5 billion-year history.
“Over a very short period of time – less than 5,000 years, or even just a few decades – the melting of titanium-rich rocks at the boundary between the moon’s core and mantle produced an extremely strong magnetic field,” lead author Claire Nicholls, associate professor of planetary processes geology at the University of Oxford, said in a statement.
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long discussion
Discussions about the moon’s magnetic field are based on a limited sample of lunar rocks. Between 1969 and 1972, six Apollo missions landed on the moon, landing in areas near the moon’s equator. According to the researchers, these missions landed in roughly the same place, in an area with similar types of rock.
It was easiest for astronauts to land their small spacecraft in a vast, flat, basalt region called Maria. Maria is an old lava plain that formed after an ancient meteorite impact melted the original rock. These Apollo landing areas are rich in titanium basalt.
A new study graphed the amount of titanium in lunar samples and the strength of the rock’s magnetization. The scientists found that rock samples with less than 6% titanium had weaker magnetic fields, while rocks with higher titanium concentrations had stronger magnetic fields.
The statement said this suggests a link between the formation of titanium-rich rocks and the generation of a strong lunar magnetic field. Researchers believe that both were caused by the melting of titanium-rich material deep within the moon, creating a temporarily extremely strong magnetic field.
limited sample
Apollo’s moon rocks make up a significant portion of Earth’s moon resources. Auction house Christie’s suggests that about 1,433 pounds (650 kilograms) of moon rocks on Earth came from meteorites. According to NASA, the Apollo archives account for approximately 842 pounds (382 kg) of that inventory.
Scientists have analyzed many of the titanium-rich Apollo stones, leading to the realization that the Moon has had a strong magnetic field for a long time, the University of Oxford said in a statement. But that seemed odd to other scientists, who argued that the moon’s core was too small, at just one-seventh of its radius, to be able to generate a strong magnetic field over long periods of the moon’s history.
The researchers checked for sampling bias by running the model, and the results showed that the set of random lunar samples the scientists analyzed contained very few rocks with strong magnetic fields. The NASA-led Artemis astronaut mission is expected to land at more diverse locations and collect samples that span the moon’s 4.5 billion-year history.
“If we were aliens exploring Earth and had landed on Earth only six times, we would probably have had a similar sampling bias, especially if we had chosen a flat surface to land on,” study co-author John Wade, associate professor of planetary materials at the University of Oxford, said in a statement. “It’s just a coincidence that the Apollo missions focused on the moon’s rare-earth regions. If they had landed elsewhere, the moon would have had only a weak magnetic field and we would have completely missed this important part of early lunar history.”
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