Our star is on the cusp of a once-in-11-years event, when its magnetic field undergoes a complete reversal. What does that mean for us?
An artist’s concept of the heliospheric current sheet, which becomes more wavy when the sun’s magnetic field flips.
The sun is about to undergo what sounds like a massive upheaval.
In the next few months, scientists say, our star will experience a complete reversal of its magnetic field. The sun’s north magnetic pole will become its south pole, and vice versa, in an event that will reverberate throughout the entire solar system.
Although this kind of solar about-face can’t help but have a certain apocalyptic, cats-and-dogs-living-together aspect to it, the phenomenon is perfectly normal—and benign. There will likely be small influences on weather patterns and, interestingly, temporarily less lightning in thunderstorms. Meanwhile, astronauts working on the International Space Station will be afforded a little extra protection against cosmic radiation. “This happens every 11 years,” solar physicist Todd Hoeksema says. “We’ve survived all the last ones.”
The imminent field inversion is a natural part of the sun’s approximately 11-year solar cycle of magnetic activity. The sun is currently going through what is known as solar maximum, when extra magnetic activity translates into greater chances of space weather-spawning events such as flares and coronal mass ejections, which can bombard the Earth with radiation and solar material. These events can trigger auroras—a nice bonus—but also disrupt satellite operations and even damage power grids on the ground (though the sun’s current cycle has been the weakest in a century).
The polarity reversal, expected in the next three to four months, will mark the midpoint of solar maximum. Over the following five and a half years, the sun’s average magnetic storminess will die down to a solar minimum, after which things will ramp right back up again.
Hoeksema and his colleagues monitor the magnetic activity at the sun’s poles from Stanford University’s Wilcox Solar Observatory. Hoeksema, who is the observatory’s director, said that the sun’s polar magnetic fields have been weakening, will zero out, and then return with opposite polarities. The north pole has apparently already switched over, essentially giving the sun two south poles for the moment. But the south pole will soon catch up, and the polarity reversal will complete itself.
The magnetic flip comes about as a result of strong, local magnetic fields associated with sunspots bursting out around the sun’s equator and then migrating poleward. This so-called magnetic flux “eats away at the existing polar field and gradually over a period of a couple years erodes all of it,” Hoeksema says. “Then more flux comes up and turns the polar field into the other direction.”
The sun’s magnetic field influences a vast, bubble-like region of space dubbed the heliosphere, which extends for billions of miles, beyond even far-out Pluto. With a polarity switcheroo in the offing, the heliosphere has been seeing some changes recently.
The heliosphere is electrically molded by the current sheet, a vast plane of weak current created by the sun’s slowly rotating magnetic fields. The current sheet extends out from the sun’s equator across the solar system, like a skirt from the waist of a twirling dancer. The current sheet “acts like a big deflector shield,” Hoeksema says, helping to protect Earth and the other planets from high-energy intruders known as galactic cosmic rays—particles that are shot out of supernovas and other violent celestial phenomena.
Within Earth’s magnetic field, all but the highest-energy galactic cosmic rays are kicked aside. But for astronauts and satellites in orbit, cosmic rays can be bad news. Like atomic bullets, cosmic rays damagingly pierce matter, including our bodies’ cells as well as machine components.
During solar maximum, the current sheet’s shape becomes rumpled compared to near solar minimum. “At this point in the cycle when polarity is reversing, the current sheet extends all the way to the [sun’s] poles,” Hoeksema says. “What that does is affect how cosmic rays from the galaxy enter the heliosphere and make their way to Earth.” The effect is beneficial: An expanded, wavy current sheet keeps more cosmic rays at bay and protects astronauts. “The sun is shielding the whole heliosphere, so we see fewer cosmic rays now than at solar minimum.”
Besides being good news for astronauts, fewer cosmic rays in the neighborhood could also have an impact on our weather. Cosmic rays ionize Earth’s upper atmosphere, which affects the formation of clouds, storms, and lightning. Terrestrial storms might be a bit less intense, therefore, around solar maximum, Hoeksema says, but the overall connection remains speculative.
Intriguing examples of correlations among the state of the current sheet, cosmic-ray peppering, and climate do exist. “Locally around the world you see places where the weather changes with a 22-year cycle related to these cosmic rays,” Hoeksema says. He pointed to drought records in the southwestern United States and tree-ring records from a variety of places, such as the Pacific coast.
Overall, the polarity reversal is “changing things on the scale of the whole solar system,” Hoeksema says. But don’t expect anything cataclysmic here on Earth.