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Meteorite memories erased by magnets, deleting billion-year-old information

In 2011, nomads who were wandering around the western Sahara came across valuable time capsules from Mars: dark coal-like pieces of a meteorite, scattered across the sand dunes. Known as “Black Beauty,” the parent body was of great interest to scientists and collectors alike due to the presence of crystals that formed on Mars over 4.4 billion years ago, making it older than any rock found on Earth. Jérôme Gattacceca, a paleomagnetist at the European Centre for Research and Teaching in Environmental Geosciences, was hopeful that it could contain a hidden message left by the now-defunct magnetic field on Mars, which is believed to have contributed to the planet’s ability to maintain an atmosphere, water, and perhaps even life.

However, when Gattacceca obtained a fragment of Black Beauty and tried to decipher its magnetic inscription, he discovered that its memory had been erased – similar to the concept depicted in the “Men in Black” movie – and replaced by a stronger signal. He immediately knew the cause of this – somewhere along its journey from the Moroccan desert to street vendors to a laboratory, the rock had come into contact with powerful hand magnets, a common technique used to identify meteorites. Gattacceca laments, “It’s regrettable that just through the use of magnets, we have destroyed this scientific information that has been stored there for four billion years.”

In a recent study, Foteini Vervelidou, a planetary scientist at the Massachusetts Institute of Technology (MIT), and her team have demonstrated the destructive impact of hand magnets, which are often made of rare-earth metals like neodymium and are usually 10,000 times stronger than Earth’s magnetic field. The researchers discovered that when brought within a few centimeters of a rock, the magnets overwrite the residual fields found in iron-based minerals such as magnetite and reset them to the higher strength and orientation of the magnet. In a flash, a unique insight into the core of distant rocky bodies can be erased. For example, Black Beauty is the sole meteorite that is old enough to “remember” the magnetic field of Mars before it began to disappear about four billion years ago.

A group of researchers, led by planetary scientist Foteini Vervelidou from MIT, have discovered that the use of hand magnets to identify meteorites can erase crucial scientific data contained within them. The magnets, which are often made from rare-earth metals and are up to 10,000 times stronger than Earth’s magnetic field, can overwrite and reset vestigial magnetic fields in iron-based minerals within the rocks, destroying valuable information that has been stored for billions of years. Vervelidou is now hoping to raise awareness about the destructive power of hand magnets and convince collectors and researchers to abandon the technique. Although hand magnets are effective in distinguishing ordinary chondrites from Earth rocks, their diagnostic abilities are limited, and the most valuable meteorites are often the ones that don’t stick to magnets. According to Ben Weiss, a planetary scientist at MIT and co-author of the study, the literature on meteorites is full of false magnetic findings caused by the use of magnets.

After discovering magnetic contamination in nine different Black Beauty samples, the researchers decided to address the hand-magnet issue in their study, which has been accepted by the Journal of Geophysical Research: Planets. They calculated how magnets of varying strengths would affect a meteorite’s magnetic records as they approached the rock. To verify their calculations, study co-author France Lagroix from the Paris Institute of Planetary Physics measured the fields in 13 samples of terrestrial basalt before and after placing a standard hand magnet at different distances from them. The results demonstrated how the magnet progressively resets fields from the outside in, providing researchers with a guide for how deeply they would need to cut to obtain an uncontaminated sample. “Now we’re 100% sure, if we weren’t already, that this is what’s happening,” Weiss remarked.

The magnetic memory of Black Beauty, a meteorite from Mars, was destroyed by magnets.NASA

The value of meteorite magnetic records is not as significant to most people, including other researchers, compared to paleomagnetists. The quick and easy hand-magnet identification method remains popular because not everyone places as much importance on magnetic fields as Ben Weiss does, according to Carl Agee, the meteoriticist at the University of New Mexico who identified Black Beauty as a Martian meteorite. Planetary scientist Hasnaa Chennaoui Aoudjehane has been trying to educate Saharan meteorite hunters on the hazards of using hand magnets for the past two decades, but the message does not always resonate. Hunters are more focused on using meteorites as a source of income to sustain their daily needs.

In a recent study, Vervelidou and her team suggest an alternative method using susceptibility meters that apply a weak magnetic field, which is better at identifying different types of meteorites and does not erase the magnetic records. However, commercial susceptibility meters are expensive, costing a few thousand dollars, and are not as straightforward to use as a simple magnet. Gattacceca and his colleagues are developing handheld susceptibility meters that cost only a few hundred dollars and have only one button.

Gattacceca hopes to encourage the use of susceptibility meters in meteorite research. He discovered that the Antarctic Search for Meteorites (ANSMET), an annual expedition financed by the National Science Foundation, had distributed small hand magnets with the ANSMET logo in the researchers’ field kits. Gattacceca considered this to be a smoking gun that would lead to their frequent use.

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