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The magnetic history of ice

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The magnetic history of ice

Next to Professor Oded Aharonson is the triaxial Helmholtz coil used to generate the magnetic field during the growth of ice samples. Credit: Weizmann Institute of Science

The history of our planet was written, among other things, in the periodic inversion of its magnetic poles. Scientists at the Weizmann Institute of Science offer a new way to read this historic record: in the ice. Their findings, which were recently published in Earth and planet science letters, could lead to a refinement of ice cores and, in the future, could be applied to understanding the magnetic history of other bodies in our solar system, including Mars and Jupiter’s Europa moon.

The idea of ​​studying a possible link between ice and the magnetic history of the Earth was born far from the source of the planet’s ice, on the sunny island of Corsica, where Professor Oded Aharonson of the Department of Science of the Earth and the planets of the Institute attended a conference on magnetism. . More specifically, the researchers discussed the field known as paleo-magnetism, which is mainly studied through flake magnetic minerals that have been trapped in rocks or nuclei drilled in oceanic sediments. These particles align with the Earth’s magnetic field when they are trapped in place, and even millions of years later, researchers can test their north-south magnetic alignment and understand the position of the Earth. magnetic poles at that distant time. It was the latter who gave Aharonson the idea: if small amounts of magnetic material could be detected in oceanic sediments, perhaps they could also be found trapped in ice and measured. Some of the frozen ice in glaciers in places like Greenland or Alaska is thousands of years old and is layered like tree rings. Ice cores drilled through them are studied to detect signs such as global warming or ice ages. Why not also reversals of the magnetic field?

The first question Aharonson and his student Yuval Grossman who led the project had to ask was whether it was possible that the process in which ice forms in regions near the poles may contain a detectable record of magnetic pole reversals. . These randomly spaced inversions have occurred throughout the history of our planet, fueled by the chaotic movement of the dynamo in liquid iron deep within the planet. heart. In striped rock formations and layered sediments, researchers measure the magnetic moment – the north-south magnetic orientations – of the magnetic materials in these materials to reveal the magnetic moment of the Earth’s magnetic field at that time. Scientists believed that such magnetic particles could be found in dust that is trapped, along with water ice, in glaciers and ice caps.

The research team constructed an experimental configuration to simulate the formation of ice like that of polar glaciers, where dust particles in the atmosphere can even provide the nuclei around which snowflakes form. The researchers created artificial snowfall by finely crushing ice made from purified water, adding a little magnetic dust and dropping it through a very cold column that was exposed to a magnetic field, the latter having an orientation controlled by scientists. By maintaining very cold temperatures – about 30 degrees Celsius below zero, they discovered that they could generate miniature “ice cores” in which snow and dust solidified solidly in hard ice.

“If the dust is not affected by an external magnetic field, it will deposit in random directions which will cancel each other out,” says Aharonson. “But if part of it is oriented in a particular direction just before the particles freeze in place, the net magnetic moment will be detectable.”

To measure the magnetism of the “ ice cores ” they had created in the laboratory, Weizmann scientists took them to the Hebrew University of Jerusalem, to Professor Ron Shaar’s laboratory, where a sensitive magnetometer installed there bottom is capable of measuring the smallest of the magnetic moments. The team found a small, but certainly detectable magnetic moment which corresponded to the magnetic fields applied to their ice samples.

“The paleo-magnetic history of the Earth was studied from the rocky file; reading it in ice cores could reveal additional dimensions, or help assign specific dates to other discoveries in these cores,” said Aharonson. “And we know that the surfaces of Mars and large icy moons like Europa have been exposed to magnetic fields. It would be exciting to look magnetic field inversions in the ice taken from other bodies in our solar system. “

“We have proven that it is possible,” he adds. Aharonson even proposed a research project for a future space mission involving the sampling of ice cores on Mars, and he hopes that this demonstration of the feasibility of measuring such a carrot will advance the attractiveness of this proposal.


Determination of the effective magnetic moment of multicore nanoparticles


More information:
Yuval Grossman et al, Experimental determination of the remanent magnetism of dusty ice deposits, Earth and planet science letters (2020). DOI: 10.1016 / j.epsl.2020.116408

Quote: The magnetic history of ice (2020, June 29) recovered on June 29, 2020 on https://phys.org/news/2020-06-magnetic-history-ice.html

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