If you’re out searching for meteorites beware the attraction

It happens surprisingly often – a meteor lights up the sky as it falls to Earth and incredible footage of the event circulated on social media. Then everyone hares off to find it. At this point experts want citizen scientists to hold up.

For most meteorites which hit the ground, scientists and citizen scientists alike are on the hunt to determine the landing sites and uncover the meteorite fragments likely scattered across the ground.

But a recent study in the Journal of Geophysical Research: Planets warns against a widely-used technique used by meteorite hunters to help identify their discoveries. Simply touching it with a hand magnet can erase a meteorite’s magnetic memory and destroy scientifically-valuable information. 

“There’s been this incredible explosion of meteorite diversity and number in the last 20 years or so, and we owe meteorite hunters a thanks for finding these things,” study author Benjamin Weiss, Professor of Planetary Sciences at Massachusetts Institute of Technology, US, told MIT News.

“But the trade-off, the devil’s bargain, is that often they are using magnets to find them and are immediately destroying their magnetic record in the process.”

Don’t use magnets to identify meteorites!

Meteorites are fragments of rocks from outer space which survive entering the Earth’s atmosphere and crash-land on the ground. Some may be rich in metals like iron and nickel, which makes them more strongly attracted to magnets than most terrestrial rocks – a characteristic that’s historically been exploited to identify them.

But, according to the study, “many of the most rare and valuable meteorites, including most Martian meteorites, are poor in magnetic minerals and therefore cannot be easily distinguished from terrestrial rocks with a magnet.”

Not only is it an inefficient method of categorising meteorites, but exposure to strong magnetic fields can remagnetise the metallic grains present and almost instantly erase invaluable records of planetary formation and evolution. 

It was the meteorite Northwest Africa (NWA) 7034, also known as “Black Beauty”, which was the tipping point for the MIT team. Containing crystals that formed on Mars more than 4.4 billion years ago when the planet had a magnetic field, multiple samples of Black Beauty have been remagnetised since landing on Earth.

A black rock with smooth sides
Designated Northwest Africa (NWA) 7034, and nicknamed Black Beauty, this Martian meteorite weighs approximately 320 grams. Credit NASA 850

“There was an incredible record there, and a unique opportunity to understand the early history of Mars’ magnetism,” Weiss told MIT News.

“But we found it’s all been obliterated by magnets.”

In their new study, the team developed a mathematical model that can calculate the magnetic fields surrounding typical hand magnets and predict their effect on rocks of various sizes.

By exposing different samples of the same terrestrial rock to varying magnetic fields, and measuring how each sample’s magnetism changed in response, they were able to show that the model can be used to determine whether a rock has been remagnetised.

It can also be used to estimate the depth at which the meteorite might still be unaffected.

The researchers recommend that meteorites should never be touched or even approached with magnets. Instead, they suggest that a “low-field susceptibility meter is a far more sensitive and completely non-destructive tool for meteorite classification.”

Keep an eye out for meteors

If you live in Australia and want to get involved in meteorite research, without having to fork out for a several thousand dollar piece of equipment, you can get involved in Fireballs in the Sky.

It’s a citizen science project linking with the research of the Desert Fireball Network – an inter-disciplinary research group part of the Space Science and Technology Centre at Curtin University, Western Australia. The Desert Fireball Network is working to uncover the mysteries surrounding the formation of the solar system through the study of meteorites, fireballs, and their pre-Earth orbits.

By downloading the Fireballs in the Sky mobile app, or using the web interface, you can report sightings of meteors to alert scientists to potentially scientifically significant events, and contribute important data to our knowledge about meteors.

You can also view sightings by other users and access information about upcoming meteor showers.

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