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.
