It has been a season of sky pageants. March 24 and 25 across the Americas, Europe, and North and East Asia. April 8 featured the in North America. March and April also brought the appearance of the evocatively named . And last weekend, earthlings were treated to a spectacular light show when a geomagnetic explosion on the sun, known as a , produced a colorful display of the aurora borealis, a phenomenon usually limited to the north polar region, but visible this time around as far south as Alabama in the U.S. and at similar latitudes around the world.
Coronal mass ejections produce not just spectacle, but potentially deadly mischief. When the energy from the sun collides with Earth, it can disrupt satellites, send GPS systems awry, knock power plants offline, and shut down telecommunications. Like hurricanes, solar storms are by the National Oceanic and Atmospheric Administration (NOAA), from minor to moderate to strong to severe to extreme.
On May 12, NOAA issued for the unfolding event, though even at its peak, from May 10 to 12, there were no reports of power or satellite disruption. But if the Earth dodged a bullet this time, we face a potentially rough year or so, as the sun goes through one of its cycles of peak activity.
So what’s going on out there, how great is the danger to us here on Earth, and how can we prepare?
What causes solar storms?
In the same way the Earth has its seasons, the sun does too. Solar seasons play out not over the course of months, however, but in 11-year cycles that produce times of high activity, known as the solar maximum, and low activity known as the solar minimum. The cycles are due to the fact that the sun is not solid, which means that different parts of its surface rotate at different rates—. This causes the sun’s magnetic field , slowly building up energy until it snaps. When that happens, the north and south magnetic poles , releasing the energy that creates the solar maximum. Once that energy is expended, the sun returns to a less volatile solar minimum.
One telltale sign of high solar activity is sunspots, small patches of twisted magnetic fields on the sun. . The current eruption was associated with a sunspot 16 times the diameter of Earth, and gave off billions of tons of plasma—.
Not every solar maximum or solar minimum is equal, however. “The main cycle of the sun is the 11-year one, but people have noticed longer trends in the sunspot activity,” says Michael Liemohn, professor of climate and space sciences and engineering at the University of Michigan. “There seems to be a century-long cycle for which the number of sunspots at solar maximum is smaller for a cycle or two and then returns to a more normal level.”
The last period of solar maximum, which ended about ten years ago, was at the lower end of the energy spectrum. The one that ended 20 years ago was higher. “We expect this current solar maximum to be bigger than the previous one, and more similar to the solar activity peak 20 years ago,” says Liemohn.
How do coronal mass ejections endanger Earth?
The best way to understand the effect solar storms have on our planet is to think of the atmosphere as akin to the gas in a fluorescent light bulb. In the bulb, Liemohn explains, electrodes at either end accelerate electrons, which interact with the gas, imparting energy to it and causing it to give off light. High in the atmosphere—50 to 200 miles up—a similar process creates the aurora. Closer to the surface of the Earth, the effect is not so benign.
“Like in the bulb, there is an electric current associated with the fast electrons, and these space currents can induce other electric currents in … conducting loops here on the ground,” says Liemohn. “The loops have to be very long, many miles, but high voltage power lines are susceptible to this effect.”
Damage to satellites is more direct and done in a number of ways. As , geomagnetic storms heat the outer atmosphere, causing it to expand. This increases the drag on satellites and can degrade their orbits. The charged particles streaming from the sun during a solar storm can also penetrate a satellite or electrify its surface, damaging its components. The problem is especially acute in satellites in high orbits, —which is the altitude at which most communications satellites fly.
Crewed spacecraft like the International Space Station orbit much lower—. That —which shields us from solar and cosmic rays on the ground. Still, astronauts receive more of a radiation dose than earthbound people and animals do, especially during a solar storm. The station or spacecraft themselves provide additional protection—but an unprotected astronaut on the surface of the moon or Mars would be in serious trouble during a solar storm. Space.com, a coronal mass ejection “shock wave” would expose the astronaut to the equivalent of 300,000 simultaneous chest x-rays, much more than the 45,000 that would prove lethal.
Getting ready for the next one
Typically, a solar storm takes a day or so to reach and pass Earth. The recent one lasted several days, Liemohn explains, because the sun released several storms in quick succession. “Earth is in the recovery phase of the storm now, which will last a few more days,” he said on May 12. “But now the aurora will be confined to its usual location at higher latitudes, across Alaska and Canada.”
More big storms are likelier than not during this powerful solar maximum. The solar weather could take until mid 2025 to start to subside, . So how can we prepare?
In 2019, Congress took a stab at hardening America’s defenses against space weather events when it passed the , for Promoting Research and Observations of Space Weather to Improve the Forecasting of Tomorrow. Under the act, Washington empowered NOAA, NASA, the , industry, academia and more to research how to prepare for adverse space weather events and to prioritize appropriate funding to that end.
“Basically,” says Daniel Welling, assistant professor in climate and space sciences at the University of Michigan, “the law is to have these bodies advise the nation on how to proceed in trying to understand and set benchmarks for space weather forecasting.”
At the moment, that’s not easy to do. For one thing, space weather is still something of a black box for researchers. For another, even if we could predict it as reliably as we can predict terrestrial weather, the U.S. power grid is so sprawling and regionalized that it’s hard to put protocols in place to protect everything.
A proof-of-concept example of what that kind of command and control system would look like, however, does exist in New Zealand.
Just over a year ago, Welling worked with a team at , the of the country’s national grid,
to model an extreme solar storm estimate and then change the grid configuration until it was stable. That was distilled down to a PDF procedure that sits on the desks of the Transpower operators. “They activated it this [past] weekend,” says Welling, “which is really cool.”
But a nation of 5.1 million covering a land mass of 103,500 square miles is different from a nation like the U.S., with its 333 million people and its 3.8 million square miles. And if a grid-killing storm hit, our power systems would likely go down. That’s not for lack of machinery and protocols in development, however. Power plant transformers operate on alternating current, but during solar storms may receive surges of direct current.
“Those transformers are not meant to handle that, so they can heat up, sometimes quite quickly,” says Welling.
A piece of hardware known as a geomagnetically induced current (GIC) blocker could be installed on the transformers to protect them from destructive pulses of power. The problem is the GIC blockers are still in development, and when they are installed, they can have what Welling calls a Whac-A-Mole effect. “You shut down the current [from the solar storm] over here, and it doubles over there,” he says.
That leaves transformers vulnerable—and vulnerabl