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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What Happens When The Poles Flip?

Have you heard the terrifying news that the Earth’s poles are going to flip? What does “flipping” mean? And if the Earth’s poles do flip, are we in any danger?

Have you heard the startling news that the Earth’s poles might flip? Perhaps in the response to a close pass from the mysterious Planet X? Are you imagining the entire Earth actually flipping over on its side or rotating upside down, possibly while Yakkity Sax plays in the background? When will this happen? Can this happen?

First, there’s no secret planet hurtling through the Solar System causing chaos and orbital disturbances. So could the Earth spontaneously physically flip over? Some planets have already been tilted and flipped.

Take a look at Uranus. Its orbital tilt is 98-degrees. We assume the planet started with the same tilt as the rest of the Solar System, and some event in the ancient past caused it to fall over. It could have collided with another planet, billions of years ago, or gravitational interactions with other giant planets pushed it over.

And then there’s Venus, its axial tilt is 177-degrees. That’s essentially upside down. Venus is turning in the opposite direction from every other planet in the Solar System. Standing on the surface of Venus, you would see the Sun rise in the West and set in the East. Astronomers don’t know why this happened, perhaps it was gravitational interactions or a collision with another planet.

To actually flip a planet off its axis would take an event so catastrophic that it would devastate the planet. Don’t worry, as far as we know, those kinds of events and interactions stopped happening billions of years ago.
That’s the good news. The Earth isn’t likely to just fall over, or get bashed on its side like an office tower under the might of Godzilla

Schematic illustration of Earth's magnetic field.   Credit/Copyright: Peter Reid
Schematic illustration of Earth’s magnetic field. Credit/Copyright: Peter Reid

Now what about those magnetic poles. On Earth, they can and do reverse on a regular basis. The Earth is often shown like a giant bar magnet, with a north magnetic pole and a south magnetic pole. Over vast periods of time, the Earth’s north pole becomes its south pole, and vice versa. Geologists measure the magnetic configuration of iron particles in ancient lava flows. in one part of the lava flow, the particles oriented with one magnetic configuration, and then in another, the particles were reversed. It turns out the planet reverses its polarity every 450,000 years, and the last reversal happened about 780,000 years ago. Which means it could happen in the next few thousand years.

If the Earth’s poles did reverse, what would happen to us? If the magnetic field disappeared entirely, the planet would be bathed in radiation from the Sun, which would likely cause an increase in cancer. But the Earth’s atmosphere would still protect us from majority of radiation.

What about mass extinctions? Scientists have wondered if there’s a link between them and magnetic reversals.
Fortunately for us, there doesn’t seem to be any connection. Whenever geomagnetic reversals happened in the past, it didn’t devastate life on Earth. So don’t worry about it.

There is a pretty good chance it won’t happen in our lifetime, and maybe not for hundreds of thousands of years. And even if the Earth’s poles flip, it wouldn’t be the end of the world. You might need to take a sharpie to your compass though.

What Will Happen When the Sun’s Magnetic Poles Reverse?

The Sun’s magnetic field will likely reverse sometime in the next three to four months. No, this is not the next doomsday prediction scenario. It really will happen. But there’s nothing to fear because in reality the Sun’s magnetic field changes regularly, about every 11 years.

The flip-flopping of the Sun’s magnetic field takes place at the peak of each solar activity cycle when the Sun’s internal magnetic dynamo reorients itself. When the field reversal happens, the magnetic field weakens, then dies down to zero before emerging again with a reversed polarity.

While this is not a catastrophic event, the reversal will have effects, said solar physicist Todd Hoeksema, the director of Stanford University’s Wilcox Solar Observatory, who monitors the Sun’s polar magnetic fields. “This change will have ripple effects throughout the Solar System,” he said.

When solar physicists talk about solar field reversals, their conversation often centers on the “current sheet.” The current sheet is a sprawling surface jutting outward from the sun’s equator where the Sun’s slowly-rotating magnetic field induces an electrical current. The current itself is small, only one ten-billionth of an amp per square meter (0.0000000001 amps/m2), but there’s a lot of it: the amperage flows through a region 10,000 km thick and billions of kilometers wide. Electrically speaking, the entire heliosphere is organized around this enormous sheet.

During field reversals, the current sheet becomes very wavy, and as Earth orbits the Sun, we dip in and out of the current sheet. This means we can see an uptick in space weather, with any solar storms affecting Earth more. So, there may be more auroras in our near future.

Cosmic rays are also affected. These are high-energy particles accelerated to nearly light speed by supernova explosions and other violent events in the galaxy. Cosmic rays are a danger to astronauts and space probes, and some researchers say they might affect the cloudiness and climate of Earth. The current sheet acts as a barrier to cosmic rays, deflecting them as they attempt to penetrate the inner solar system. The good news is that a wavy sheet acts as a better shield against these energetic particles from deep space.

Scientists say the Sun’s north pole is already quite far along losing its polarity, with the south pole coming along behind.

“The sun’s north pole has already changed sign, while the south pole is racing to catch up,” said Phil Scherrer, another solar physicst at Standford. “Soon, however, both poles will be reversed, and the second half of Solar Max will be underway.”

Meaning that activity in this already weak solar cycle will start to abate.

Source: NASA