Scientists have revealed that the mysterious magnetism found in rocks retrieved during the Apollo moon missions are of natural origin and not a result of spacecraft-induced effects, effectively debunking one of the major challenges to the theory that the moon generates its own magnetic field.
Officials made the findings after exposing eight rock samples from four Apollo missions to strong magnetic fields, simulating the conditions experienced during the return journey from the moon.
The samples were then subjected to a field strength of 5 millitesla for two days, equivalent to about 100 times Earth's magnetic field strength. Remarkably, the researchers observed that the "magnetic contamination" could be easily removed using standard methods.
"You want to know that the spacecraft returning your sample is not magnetically frying your rock, essentially. We simulated a long-term exposure of a sample to a stronger magnetic field than what the Earth has... and found that for nearly all samples, including several we had previously studied in the context of lunar dynamo records, we could remove that contamination quite easily," said lead study author Sonia Tikoo, an assistant professor of geophysics at the Stanford Doerr School of Sustainability.
The enigma of the moon's magnetism dates back to the 1980s when geophysicists studying moon rocks brought back from the Apollo missions detected strong magnetic fields embedded within the lunar samples. Given the moon's relatively small size, it seemed unlikely it could maintain such a magnetic field for over 1.5 billion years.
Researchers had previously speculated that sources other than the moon itself, including the spacecraft used to transport the samples, may have caused this magnetization.
"As a global community, we’re starting to send more sample-return missions to other bodies, so it’s good to know that as long as we’re careful to ensure spacecraft fields are not too high – and it doesn’t have to be zero, necessarily – we can still do paleomagnetism studies along with other research," said Tikoo.
The study's findings were published Wednesday in the journal Geophysical Research Letters.