Unlike the Earth, the moon is naked.
The dusty rock is free of a magnetic field, meaning it’s vulnerable to harmful solar radiation that can flare off the sun at more than 1,000 miles per second. But that wasn’t always what scientists had believed.
After the Apollo missions that landed the first humans on the moon 52 years ago, scientists collected data that showed samples had magnetization, suggesting the moon may have been clothed with a magnetic field at some point during its 4.53 billion-year history.
Researchers thought that magnetization was caused by a “geodynamo” similar to that of Earth’s. The idea is that the magnetic field was being generated by the mingling of liquid iron deep in the moon’s core, giving off electric currents.
But more advanced technology has since put the theory to rest, at least according to John Tarduno, a geophysics professor at the University of Rochester in New York.
“The core of the moon is really small and it would be hard to actually drive that kind of magnetic field. Plus, the previous measurements that record a high magnetic field were not conducted using heating experiments,” Tarduno said in a statement. “They used other techniques that may not accurately record the magnetic field.”
Now, Tarduno and colleagues from seven other institutions say the moon never had a magnetic field after analyzing moon samples from the Apollo missions of the 1960s and ‘70s with advanced carbon dioxide lasers and highly sensitive magnetometers.
This means that for billions of years, the moon has been bombarded with solar wind that may have been dousing lunar soil with different kinds of volatiles, or compounds that are “easily evaporated,” including carbon, hydrogen, water and helium 3 — a specific version of helium that is scarce on Earth.
It also means the moon’s soil may be a record book of past solar wind activity, helping scientists better understand the evolution of the sun.
The study’s findings, which were published Aug. 4 in the journal Science Advances, may aid “a new age of space exploration” beginning in 2024 when NASA sends astronauts back to the moon as part of their Artemis mission. One of the administration’s goals is to determine if such materials can be extracted for use on Earth.
Helium 3, for example, could be a future source of fuel; it’s currently used in medical imaging and cryogenics.
The team, led by Tarduno, heated lunar samples from a 2 million-year-old crater with a special CO2 laser and measured their magnetic signals in ways that protected the rocks from any damage.
Researchers found that the magnetization earlier scientists detected in the samples could have come from meteorite or comet impacts that blasted the moon’s surface. What’s more, samples that had the potential to give off strong magnetic signals failed to emit any, suggesting the moon never had a magnetic field.
“If there had been a magnetic field on the moon, the samples we studied should all have acquired magnetization, but they haven’t,” Tarduno said in a statement. “That’s pretty conclusive that the moon didn’t have a long-lasting dynamo field.”
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