Humans Are Erasing Billions of Years of Data From Ancient Meteorites

Inadvertently destroying priceless information contained inside is a common and simple approach for determining whether or not a rock is a meteorite and what sort of meteorite it is.

Researchers from MIT in the US and Paris Cité University in France discovered that the magnetic record kept inside ferromagnetic crystals in meteorites is erased and overwritten by the usage of rare-earth magnets like neodymium. Due to the high iron content of many meteorites that impact Earth, we are losing crucial information on how magnetic fields in space have shaped these meteorites over the course of billions of years.

"Meteorites offer priceless evidence of planetary development and creation. The history of planetary dynamos, the thermal development and differentiation of planetesimals, and the accretion in the protoplanetary disk have all been restricted by research on the paleomagnetism of these bodies.

A team lead by planetary scientist Foteini Vervelidou of MIT writes, "However, the potential of these magnetic recordings in furthering the area of planetary research is severely impeded by a frequently utilized technique: application of hand magnets to help in meteorite categorization.

The magnetic record of a meteorite is nearly instantly destroyed when it comes into contact with a magnet.

Interesting changes in minerals can result from exposure to a magnetic field. Magnetic minerals include crystals that can align with the magnetic field during the formation of a piece of rock and, in certain circumstances, become magnetized themselves, leaving a trace of the direction and strength of the magnetic field that generated it.

Scientists use these data to learn about the history of the Earth's magnetic field and how it has changed and developed over time. The study of these records is known as paleomagnetism here on Earth. Because of the abundance of such recordings in the earth beneath us, we have gained a great deal of knowledge about our ever-evolving home planet.

Similar records are likely to be preserved on other stony planets, but our ability to retrieve them is obviously far more limited. For instance, there is a lot of curiosity in Mars. A revolving, convecting, conducting fluid located deep within the earth, known as a dynamo, creates the magnetic field that surrounds us.

Now, Mars lacks a functioning dynamo, and it is unknown why its whole magnetic field vanished. Old rocks from Mars might provide further information about the time when the planet did have an active dynamo, and occasionally, very seldom, ancient rocks from Mars do reach Earth.

One prominent example is the Black Beauty meteorite, also known as Northwest Africa 7034, which was discovered in the Moroccan desert sands in 2011. One of the oldest Martian meteorites found on Earth, it has pieces that have been dated to as far back as 4.4 billion years, when the Solar System and the planets that make up its core were still young.

When scientists went to verify magnetic recordings in rock fragments, they discovered nothing—not even a trace—of the dynamo that Mars was assumed to have at the time. Any magnetic remnants of Mars that could have been present in NWA 7034 after it had made its way to Earth had been destroyed by the magnets employed by meteorite hunters to confirm their discovery.

Many meteorites have shown this phenomena, but no one has looked at how it works in detail. As a result, Vervelidou and her coworkers carried out a multi-step research that included numerical modeling, the remagnetization of terrestrial basalt using hand magnets, and an examination of 9 shards of the parent meteorite that gave rise to NWA 7034.

They started by estimating the magnitude of the magnetic field that would surround a hand magnet and the impact it would have on various-sized pebbles. They next used pieces of Earth basalt to verify the accuracy of their estimations by measuring the magnetization of the rock before and after it had been exposed to a neodymium magnet.

After being subjected to the hand magnet, several of the pieces underwent total demagnetization, while others exhibited partial demagnetization similar to that seen in meteorite chunks.

The stone had been erased, according to the 2014 examination of NWA 7034, although it is possible that other pieces of the parent meteorite still contain remnants of the original magnetic record. Testing these additional pieces was the research's next step. However, Vervelidou and her team discovered that not a single piece contained any indication of these data. They had all been entirely forgotten.

The study did, however, demonstrate that magnetic disruption progresses and follows a comparable demagnetization curve. In order to locate samples that still have fossilized magnetic fields, either from planetary processes or the Solar System itself, scientists researching the magnetization of meteorites in the future might use this information as a reference to how deep the demagnetization may go.

Meanwhile, methods that can identify meteorites without erasing the sensitive interior data are already in existence.

Several studies have demonstrated the effectiveness of using magnetic susceptibility meters as a non-destructive and precise method for classifying and identifying meteorites. According to the researchers, they may be used to identify not just between meteorites and terrestrial rocks but also between various species of meteorites.

We are still optimistic that more paired NWA 7034 stones and fresh Mars meteorite discoveries will be discovered in the near future and will be free of magnet remagnetization.

The research has been published in JGR Planets.