Our planet's history has up until now been studied through the Earth's magnetic poles. However, scientists from the Weizmann Institute of Science have now developed a new way to read this historical record: in ice, which has the potential of helping future scientists discover the history of other bodies in our Solar System.
The new method derives from a field of research called paleo-magnetism, which focuses on the study of magnetic mineral flakes that were trapped in rocks or cores drilled from ocean sediments. At the time of their trapping, these flakes aligned with the Earth's magnetic field, and even millions of years later, researchers can test their magnetic north-south alignment and understand the position of the Earth's magnetic poles at that distant time.
Prof. Oded Aharonson, from the Weizmann Science Institute in Rehovot, was at a paleo-magnetism conference on the island of Corsica located in the Mediterranean Sea, near France, when he posed the question: "If small amounts of magnetic materials could be sensed in ocean sediments, maybe they could also be trapped in ice and measured."
“The Earth’s paleo-magnetic history has been studied from the rocky record; reading it in ice cores could reveal additional dimensions, or help assign accurate dates to the other findings in those cores,” he said. “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 for magnetic field reversals in ice sampled from other bodies in our Solar System.”
The Earth is home to many frozen glaciers that are millions of years old, layered like tree rings. Located in places such as Greenland and Alaska, Ice cores are often drilled in them to investigate signs of planetary warming or ice ages. Aharonson wanted to know if, during this drilling, scientists could research the magnetic fields as well.
To answer the question, the research team, led by Aharonson and his student Yuval Grossman, set out to discover if it was possible that the process in which ice forms in regions near the poles could contain a detectable record of magnetic pole reversals.
In order to do this, the research team built an experimental setup to simulate the ice formation that occurs in polar glaciers, where they theorized that dust could have gotten trapped along with these magnetic particles, together with water and ice in glaciers and ice sheets.
To do this, researchers created artificial snowfall by finely grinding ice made from purified water, adding a bit of magnetic dust, and letting it fall though a very cold column that was exposed to a magnetic field, the latter having an orientation controlled by the scientists. They found that by maintaining very cold temperatures – around 30° Celsius below zero - they could generate miniature “ice cores” in which the snow and dust froze into ice.
"It would be exciting to look for magnetic field reversals in ice sampled from other bodies in our Solar System. If the dust is not affected by an external magnetic field, it will settle in random directions which will cancel each other out,” Aharonson said.
In order to measure the magnetism in the miniature ice core models the research team had created, they needed to take it to the lab of Prof. Ron Shaar at the Hebrew University of Jerusalem, where they used a sensitive magnetometer that could detect the very slightest of magnetic "moments." The team did indeed find a small but definitely detectable magnetic moment that matched the magnetic fields applied to their ice samples. “We’ve proved it is possible,” Aharonson said. He then proposed a research project for a future space mission involving ice core sampling on Mars, adding that he hopes that this demonstration of the feasibility of measuring such a core will advance the proposal's appeal.