Testing the damage hand magnets used by amateurs do to meteorites
A pair of Earth, atmospheric and planetary scientists at Massachusetts Institute of Technology has shown how the magnetic field of a meteorite can be damaged by amateur collectors using hand magnets. In their paper published in Journal of Geophysical Research: Planets, Foteini Vervelidou and Benjamin Weiss describe how they tested the impact on the magnetic field of terrestrial basalt—as a stand in for meteorites—when it is exposed to hand magnets and what they learned by doing so.
Back in 2011, nomads in the Sahara Desert came across dark black chunks of rock atop a field of sand. Suspecting they might be valuable, they collected them and brought them to town for trade. Eventually, the rocks attracted the attention of local scientists who purchased them and brought them to a lab for testing.
That testing showed the rocks to be chunks of a meteorite that has come to be known as "Black Beauty." Testing also showed that crystals inside of the meteorite had formed on Mars, approximately 4.4. billion years ago. Unfortunately, testing of its magnetic field showed that it had been wiped away and replaced with a stronger signal—the result of testing done by amateurs with a hand magnet.
Magnetic field disruption in meteorites had been seen before, and it has been seen many times since Black Beauty was found, but until now, no one has taken the time to actively study the process. In this new effort, that is what the research pair have done—using terrestrial basalt as a stand-in for meteorites.
In testing the impact of a hand magnet on 13 samples, which the research pair note, are typically made of rare-earth metals, they found that moving them to within inches of basalt samples led to magnetic fields in the rocks being irretrievably erased and replaced by the magnetic field of the hand magnetic.
They note doing so is similar to placing a strong magnet near a computer hard drive—all the data is erased. But they also found that magnet disruption was progressive and that allowed them to create a guide for researchers looking to study meteorites in the future, letting them know how deep they would have to cut into a meteorite to reach a pristine sample. The pair also relate how the loss of magnetic field data from Black Beauty was particularly devastating because it could have provided clues about the magnetic field on Mars that once shielded its atmosphere from depletion.
The research pair conclude their paper by asking that people who find meteorites not use magnets on them. If they think a rock might be valuable, they suggest having it tested by a professional.
More information: Foteini Vervelidou et al, Hand magnets and the destruction of ancient meteorite magnetism, Journal of Geophysical Research: Planets (2023). DOI: 10.1029/2022JE007464
Journal information: Journal of Geophysical Research: Planets
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