Astronomy Cast Ep. 442: Destroy and Rebuild Pt. 6: Magnetic Pole Reversal

If we look back into the geologic record of the Earth, it appears that our planet’s magnetic field flips polarity every few hundred thousand years or so. Why does this happen? When’s it supposed to happen next? Is it dangerous?

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Is Earth’s Magnetic Field Ready to Flip?

Illustration of the invisible magnetic field lines generated by the Earth. Unlike a classic bar magnet, the matter governing Earth's magnetic field moves around. The flow of liquid iron in Earth's core creates electric currents, which in turn creates the magnetic field. Credit and copyright: Peter Reid, University of Edinburgh
Illustration of the invisible magnetic field lines generated by the Earth. Unlike a classic bar magnet, the matter governing Earth’s magnetic field moves around. The flow of liquid iron in Earth’s core creates electric currents, which in turn creates the magnetic field. Credit and copyright: Peter Reid, University of Edinburgh

Although invisible to the eye, Earth’s magnetic field plays a huge role in both keeping us safe from the ever-present solar and cosmic winds while making possible the opportunity to witness incredible displays of the northern lights. Like a giant bar magnet, if you could sprinkle iron filings around the entire Earth, the particles would align to reveal the nested arcs of our magnetic domain. The same field makes your compass needle align north to south.

We can picture our magnetic domain as a huge bubble, protecting us from cosmic radiation and electrically charged atomic particles that bombard Earth in solar winds. Satellites and instruments on the ground keep a constant watch over this bubble of magnetic energy surrounding our planet. For good reason: it’s always changing.

Earth's magnetic field is thought to be generated by an ocean of super-heated, swirling liquid iron that makes up its the outer core 1,860 miles (3000 kilometers) under our feet. Acting like the spinning conductor in one of those bicycle dynamos or generators that power lights, it generates electrical currents and a constantly changing electromagnetic field. Other sources of magnetism come from minerals in Earth’s mantle and crust, while the ionosphere, magnetosphere and oceans also play a role. The three Swarm satellites precisely identify and measure precisely these different magnetic signals. Copyright: ESA/ATG Medialab
Earth’s magnetic field is thought to be generated by an ocean of super-heated, swirling liquid iron that makes up its the outer core 1,860 miles (3000 kilometers) under our feet. Acting like the spinning conductor similar to a bicycle dynamo that powers a headlight, it generates electrical currents and a constantly changing electromagnetic field. Other sources of magnetism come from minerals in Earth’s mantle and crust, while the ionosphere, magnetosphere and oceans also play a role. The three Swarm satellites precisely identify and measure precisely these different magnetic signals. Copyright: ESA/ATG Medialab

The European Space Agency’s Swarm satellite trio, launched at the end of 2013, has been busy measuring and untangling the different magnetic signals from Earth’s core, mantle, crust, oceans, ionosphere (upper atmosphere where the aurora occurs) and magnetosphere, the name given to the region of space dominated by Earth’s magnetic field.

At this week’s Living Planet Symposium in Prague, Czech Republic, new results from the constellation of Swarm satellites show where our protective field is weakening and strengthening, and how fast these changes are taking place.


Based on results from ESA’s Swarm mission, the animation shows how the strength of Earth’s magnetic field has changed between 1999 and mid-2016. Blue depicts where the field is weak and red shows regions where the field is strong. The field has weakened by about 3.5% at high latitudes over North America, while it has grown about 2% stronger over Asia. Watch also the migration of the north geomagnetic pole (white dot).

Between 1999 and May 2016 the changes are obvious. In the image above, blue depicts where the field is weak and red shows regions where it is strong. As well as recent data from the Swarm constellation, information from the CHAMP and Ørsted satellites were also used to create the map.


The animation shows changes in the rate at which Earth’s magnetic field strengthened and weakened between 2000 and 2015. Regions where changes in the field have slowed are shown in blue while red shows where changes sped up. For example, in 2015 changes in the field have slowed near South Africa but changes got faster over Asia. This map has been compiled using data from ESA’s Swarm mission.

The animation show that overall the field has weakened by about 3.5% at high latitudes over North America, while it has strengthened about 2% over Asia. The region where the field is at its weakest – the South Atlantic Anomaly – has moved steadily westward and weakened further by about 2%. Moreover, the magnetic north pole is also on the move east, towards Asia. Unlike the north and south geographic poles, the magnetic poles wander in an erratic way, obeying the movement of sloshing liquid iron and nickel in Earth’s outer core. More on that in a minute.

The ‘South Atlantic Anomaly’ refers to an area where Earth's protective magnetic shield is weak. The white spots on this map indicate where electronic equipment on a TOPEX/Poseidon satellite was affected by radiation as it orbited above. Credit: ESA/DTU Space
The ‘South Atlantic Anomaly’ refers to an area where Earth’s protective magnetic shield is weak. The white spots on this map indicate where electronic equipment on a TOPEX/Poseidon satellite was affected by radiation as it orbited above. The colors indicate the strength of the planet’s magnetic field with red the highest value and blue the lowest.  Credit: ESA/DTU Space

The anomaly is a region over above South America, about 125-186 miles (200 – 300 kilometers) off the coast of Brazil, and extending over much of South America, where the inner Van Allen radiation belt dips just 125-500 miles (200 – 800 kilometers) above the Earth’s surface. Satellites passing through the anomaly experience extra-strong doses of radiation from fast-moving, charged particles.

This cutaway of planet Earth shows the familiar exterior of air, water and land as well as the interior: from the mantle down to the outer and inner cores. Currents in hot, liquid iron-nickel in the outer core create our planet's protective but fluctuating magnetic field. Credit: Kelvinsong / Wikipedia
This cutaway of planet Earth shows the familiar exterior of air, water and land as well as the interior: from the mantle down to the outer and inner cores. Currents in hot, liquid iron-nickel in the outer core create our planet’s protective but fluctuating magnetic field. Credit: Kelvinsong / Wikipedia

The magnetic field is thought to be produced largely by an ocean of molten, swirling liquid iron that makes up our planet’s outer core, 1,860 miles (3000 kilometers) under our feet. As the fluid churns inside the rotating Earth, it acts like a bicycle dynamo or steam turbine. Flowing material within the outer core generates electrical currents and a continuously changing electromagnetic field. It’s thought that changes in our planet’s magnetic field are related to the speed and direction of the flow of liquid iron and nickel in the outer core.

Chris Finlay, senior scientist at DTU Space in Denmark, said, “Swarm data are now enabling us to map detailed changes in Earth’s magnetic field. Unexpectedly, we are finding rapid localized field changes that seem to be a result of accelerations of liquid metal flowing within the core.”

The magnetic field and electric currents in and around Earth generate complex forces that have immeasurable impact on every day life. The field can be thought of as a huge bubble, protecting us from cosmic radiation and charged particles that bombard Earth in solar winds. It’s shaped by winds of particles blowing from the sun called the solar wind, the reason it’s flattened on the “sun-side” and swept out into a long tail on the opposite side of the Earth. Credit: ESA/ATG medialab
The magnetic field and electric currents in and around Earth generate complex forces that have immeasurable impact on every day life. The field can be thought of as a huge bubble, protecting us from cosmic radiation and charged particles that bombard Earth in solar winds. It’s shaped by winds of particles blowing from the sun called the solar wind, the reason it’s flattened on the “sun-side” and swept out into a long tail on the opposite side of the Earth. Credit: ESA/ATG medialab

Further results are expected to yield a better understanding as why the field is weakening in some places, and globally. We know that over millions of years, magnetic poles can actually flip with north becoming south and south north. It’s possible that the current speed up in the weakening of the global field might mean it’s ready to flip.

Although there’s no evidence previous flips affected life in a negative way, one thing’s for sure. If you wake up one morning and find your compass needle points south instead of north, it’s happened.

Geomagnetic Reversal

Magnetic Field

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Geomagnetic reversal is when the orientation of the Earth’s magnetic field becomes reversed. Thus, magnetic north and south switch places. The process is a gradual one though that can take thousands of years. The possibility that the magnetic field could reverse was first brought up in the early 1900’s. However, at this time scientists did not understand the Earth’s magnetic field very well so they were not interested in the concept of geomagnetic reversal. It was not until the 1950’s that scientists began a more in-depth study of geomagnetic reversal.

Scientists have not reached a consensus on what causes pole reversal. Some believe that it is simply an effect of the nature of the planet’s magnetic field. They base this hypothesis on the magnetic field lines’ tendency to move around and think that it becomes agitated enough to flip. Other scientists propose that external influences cause the shift. For example, a tectonic plate that undergoes subduction and goes into the Earth’s mantle may disturb the magnetic field enough to make it turn off. When the field restarts, it randomly chooses orientation, so it could shift.

 In order to better understand the process, scientists study past geomagnetic reversals. This is possible because the reversals have been recorded in minerals found in sedimentary deposits or hardened magma. Scientists have discovered that the magnetic field has actually reversed thousands of times. Scientists also discovered a record of reversals on the ocean floor.

The time between geomagnetic eruptions is not constant. One time, five reversals occurred over a period of a million years. Sometimes however, none happen for a very long time. These periods are known as superchrons. The last time a geomagnetic reversal occurred was 780,000 years ago and is referred to as the Brunhes-Matumaya reversal.

Geomagnetic reversal has also been linked to 2012. Some people believe that in 2012 when the Mayan calendar runs out we will experience some cataclysmic event that will destroy our world or life as we know it. There are various theories for exactly what this event is. One theory says that geomagnetic reversal will occur during 2012. Since the magnetic field is weaker at first when it switches, some claim that the Earth will be ravaged by solar rays. Scientists still have not determined what effects a geomagnetic reversal will have on humans; however, humans did survive the last reversal 780,000 years ago. One hypothesis is that the solar winds actually create a magnetic field sufficient enough to protect us while Earth’s magnetic field restarts.

Universe Today has articles on no geomagnetic reversal in 2012 and field reversal may take 7000 years.

For more information, you should check out geomagnetic flip may not be random and magnetic storm.

Astronomy Cast has an episode on magnetism everywhere.

Reference:
NASA: Earth’s Inconstant Magnetic Field