It’s not something that’s ever happened in human history so it’s not something we think about too often, but Earth’s magnetic poles flip on a regular basis—at least, a regular basis on a geologic scale. And every time the poles flip, the magnetic field that shields our planet from deadly cosmic rays also flips. The next flip, according to new data collected by the European Space Agency, is coming up sooner than scientists expected.
Earth's magnetic field is rooted deep inside the planet. The solid inner core, which is about two-thirds the size of the Moon, is made primarily of iron and is super-heated to almost 10,300 degrees Fahrenheit.
Surrounding this solid core is a thick layer made up of iron, nickel, and small amounts of other metals in a liquid state. Differences in temperature, pressure, and the composition of the outer, liquid core causes convection, and as these metals flow, they generate electric currents that in turn produce magnetic fields. Because the Earth is spinning on its axis, these magnetic fields align to form one giant magnetic field that envelops the planet.
But the polarity of this massive magnetic field isn’t constant. Over the last 20 million years the Earth has settled into a pattern wherein the poles change polarity every 200,000 to 300,000 years; magnetic north becomes south and vice versa. It’s neither a fast nor a clean process. A flip actually takes hundreds of thousands of years, and over the course of that time the magnetic fields tug at one another, with magnetic poles emerging at odd latitudes.
It’s by measuring the variations in the magnetic field that scientists find indications that a polar flip is imminent. ESA’s Swarm mission is a magnetic field mission that uses an array of three satellites to unravel the mysteries of the Earth’s magnetic field.
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