Conducting measurements at the paleomagnetism lab at MIT.
Prior to the start of my Marie Curie project, I have been processing numerical data and have been writing equations. I understood what these data and these equations represent but I was missing the tangible experience: I wanted to touch magnetized rocks, measure myself their magnetic field and understand the details of this physical process that allows them to obtain and retain magnetization. The rocks, when many together, are able to produce a signal so strong that can be captured by a spacecraft flying hundreds of kilometers above the surface of a planetary body. I wanted to have the chance to study some of them and understand how they contribute to this massive signal. I am not the only one. There are many researchers who do precisely that, study the magnetic signal and the magnetic properties of rocks at the centimeter- down to nanometer-scale. Their field of research is called rock magnetism and paleomagnetism. ‘Paleo‘ in Greek means old. By studying the magnetic field of rocks, one studies the past magnetic field, the paleo-magnetic field.
During my Marie Curie project I have had the chance to conduct measurements at two different paleomagnetic laboratories, at MIT, USA and at IPGP, France.
Hand magnets and the destruction of ancient meteorite magnetism
My first paleomagnetic project was a high-risk high-gain one. We wanted to study the magnetization of the oldest Martian meteorite available on Earth, with minerals dated to be 4.4. billion years old, the NWA 7034 and its paired stones. This pairing group is unique and very precious because parts of it crystallized when the Martian dynamo was still active. It had therefore the potential to allow us to estimate the intensity of the magnetic field generated by the Martian dynamo. However, we found that all the samples we were able to acquire, either from private collectors or as loans from museums and universities, had their primary magnetic record completely erased by hand magnets. Hand magnets are small and powerful magnets widely used by meteorites hunters to identify meteorites. Bringing, however, a magnetized rock in contact with a hand magnet results in the magnetic record of the rock being overwritten. We reported our findings in a scientific journal in order to spread the message about the destructive effects of hand magnets and advocate in favor of an alternative identification technique: the use of hand-held susceptibility meters. Such a susceptibility meter has been designed by Minoru Uehara (CEREGE, CNRS, France) precisely for that purpose.
Scientists using the susceptibility meter designed by Minoru Uehara, CEREGE, to identify meteorites during a meteorite hunting expedition in Atacama desert, in Chile. Photo credit: Gabriel Pinto.