This Month in Science: A Shifting Magnetic Field

If you have ever used a compass to find your way, you have taken advantage of Earth’s magnetic field. The little needle that swings to the north is responding to this magnetic field and orienting toward the north pole. Today, you are more likely to navigate by the GPS (Global Positioning System) app on your phone, but GPS also relies on the Earth’s magnetic field to guide you1. While this field is useful for navigation, it serves another important purpose: protection from harmful cosmic radiation2. Also called the magnetosphere, the magnetic field is an essential part of what makes our planet habitable for life.

Earth is essentially a giant magnet. All magnets produce a field around them that travels from their north pole to their south pole. Earth’s magnetosphere is produced by motion of liquid iron within its core. The innermost core of Earth is a ball of extremely hot iron under such great pressure that it is actually solid, despite being heated to its melting point. The temperature of the core is around 6,000°C, about the same temperature as the surface of the Sun. The outer core experiences less pressure, resulting in a molten iron that swirls around the solid inner core3. The action of this swirling molten core, combined with the rotation of the Earth, produces electrical currents that create the magnetic field that surrounds our planet4.

The magnetosphere does not exist at a constant strength across the planet. The swirling currents of the outer core have ebbs and flows which directly affect the strength of the field at any given location.  All over the planet, some pockets of the magnetic field are weakening, while others are strengthening. These constant changes result in a tug-of-war at the poles1. Earth’s magnetic north pole is currently moving away from Canada toward Siberia at a rate of about 55 km (34 miles) per year5. While most published data are on the northern magnetic pole, the southern magnetic pole also wanders due to these shifting currents within the core6.

A precise knowledge of the strength and location of the magnetic poles is necessary for navigation systems to work properly. As a result of these wandering poles, the World Magnetic Model was updated January 30, 2019, earlier than its planned date in 2020 to ensure that GPS systems remain accurate1. In addition to these shifting poles, the entire magnetic field appears to be weakening at a rate of about 10% per 100 years7.

This weakening, in combination with the pole shifts, could be an indication that the poles might be heading towards a complete flip—the north pole becomes the south and vice versa. The magnetic poles have flipped about 170 times during the past 100 million years. The most recent reversal was around 780,000 years ago4. Researchers have determined these numbers by looking at metal oxide particles within lava rocks. As liquid lava cools into solid rock, the metal oxide particles orient themselves toward the direction of the strongest magnetic field. By correlating these data with the age of a rock, researchers can determine the historic position of the magnetic field4.

When the poles are in a state of reversal, it takes hundreds to thousands of years for them to complete the process. Researchers don’t currently know what causes the poles to flip, but they do know the magnetic field weakens prior to a reversal, and continues to weaken becoming erratic during the reversal8. Because the magnetosphere is essential for protection from cosmic radiation, this weakening can leave both living inhabitants and electronics susceptible to this radiation. While we don’t know for sure how the planet would be affected, scientists suggest that communication and navigation systems, and power grids might experience trouble4. Disruptions could be similar to what happens during solar flares, but potentially more dramatic. Despite the current weakening of the field, a recent study suggests that we are not in immediate danger of a pole reversal8.



Previous Columns

January 2019: Giant Ground Sloth
December: Snowflakes
November: Citizen Science
October: Parker Solar Probe Voyaging to the Sun
August: Sea Turtle Season
July: Plastic Free July
June 2018: All About Alligators

Earth's Magnetic Field
An illustration of how the magnetic poles differ from the geographic poles.
Credit: Peter Reid

Earth's Core
Illustration showing the liquid outer core and solid inner core.
Credit: ExtremeTech

Shifting Magnetic North Pole
Credit: Nature

Earth's Magnetic Field Lines
Computer model of field stability and instability during a reversal.
Credit: NASA/Gary Glazmaier, CC BY
814 Market Street • Wilmington, NC 28401 • Phone 910-798-4370 • Fax 910-798-4382