On Friday, February 17, a part of the sun erupted. A piercingly bright flash of light—a solar flare—shone briefly from the left limb of our star, where it was captured in an ultraviolet image by NASA’s Solar Dynamics Observatory spacecraft.
“It wasn’t the largest in history by any means, but it was a significant X flare,” Thomas Berger, a solar physicist and director of the Space Weather Technology, Research, and Education Center at the University of Colorado Boulder. (The “X” refers to the letter grading system of solar flare intensity, which ranges from minor A-class to severe X-class flares. “Solar flares of that magnitude will generally cause some radio-interference on the sunlit side of the Earth for an hour or two,” he says. Ultimately, this one was fairly mild—the most powerful solar flare ever recorded, in 2003, was more than 100 times more powerful by comparison—and did not cause any major problems.
That said, we’re about to enter a more volatile chapter in the sun’s 11-year cycle of magnetic activity. Solar flares are one of three major forms of solar-eruption activity, along with coronal mass ejections and radiation storms, which are likely to increase in frequency over the next few years, according to Berger.
”We are in the rising phase of Solar Cycle 25, and it is expected that activity is going to increase,” he says. (It’s known as Solar Cycle 25 because scientists first began keeping detailed records of sunspots in 1755, and there have been 25 cycles since that time.) The peak of this period, known as the solar maximum, should occur around 2025. The last solar maximum was in 2014.
That rise in activity that could majorly impact planned space activities, such as the rapidly growing constellations of low-Earth orbit satellites. And a 2025 solar maximum would coincide with NASA’s Artemis III, which aims to return humans to the surface of the moon—not the safest place to be during a solar radiation storm.
“It’s going to be a really interesting time if we get an extreme storm in this solar cycle,” Berger says.
What is the solar magnetic cycle?
The sun is a giant sphere of roiling, superheated plasma that is essentially electrically charged gas with monstrously powerful magnetic fields.
For reasons astronomers don’t yet understand, the activity of these magnetic fields increases and decreases over an 11-year cycle. The cycle also includes changes in the dark areas on the star’s surface, otherwise known as sunspots, with more spots appearing as the sun moves toward solar maximum.
“Sunspots are the source of solar magnetic eruptions,” Berger says. “The bigger the sunspot, the bigger the explosion. The more active the sun, the more sunspots, and the bigger the sunspots get.”
The current solar cycle stands out so far in a big way: So far, it’s more active than forecast by groups like the the National Oceanic and Atmospheric Administration’s Space Weather Prediction Center, with more sunspots showing up on the sun that predicted.
“We don’t know if it will continue to be more active than the forecast,” Berger says. “It’s fairly early on in the game here and could regress back to that weak forecast any month.”
Will solar eruptions disrupt Earth in 2025?
Solar eruptions occur when the magnetic field lines in a sunspot get twisted and snap, Berger says, causing an explosion with three possible outcomes.
The first is a solar flare, like that seen on February 17, which is primarily a release of photons. The second is a coronal mass ejection, or a large release of plasma into interplanetary space. And the third is a radiation storm fueled by accelerating energy particles like protons, elections, and ions. Coronal mass ejections can also sometimes generate a radiation storm by pushing charged particles in front of them as they speed through space.
Solar flares, if intense enough, can cause radio interference on the sunlit side of the Earth. Coronal mass ejections are the outbursts that really cause issues. The charged plasma can generate a geomagnetic storm when it hits our planet’s magnetosphere, resulting in awe-inspiring auroras at the poles, while also wreaking havoc on both power grid technology and satellite technology, Berger says. A big geomagnetic storm can heat the atmosphere so that it swells, dragging on low-flying satellites and even pulling some from orbit, as was the doomed case of 40 newly launched Starlink satellites on February 4, 2022.
Not every coronal mass ejection will reach Earth, however. Many, like the ejection associated with the February 17 eruption, fly off into space away from our planet. The question is whether any more will be aimed our way as we hurtle toward the solar maximum.
“Recent research is really beginning to confirm that almost every solar cycle has a really, really big eruption,” Berger says, “So it’s really just a matter of what direction in space it’s going.”
How do we plan for the sun’s unruly future?
Really powerful solar eruptions can lead to geomagnetic storms that damage electronics on the ground, such as the the storm in 1989 that knocked out some power grids. But the risks are higher today than in 1989, if just because there’s a lot more technology, and people, in space on a regular basis. For instance, there were more than 5,700 satellites in orbit at the end of 2022, while there were less than 500 satellites in 1989.
“If we do get an extreme geomagnetic storm now, there’s so much stuff up there that’s going to be moving all over the place,” Berger says. “We are concerned with an elevated risk of collision from the next one.”
[Related: What happens when the sun burns out?]
With NASA planning on heading back to the moon and eventually to Mars, scientists will need to get a lot better at forecasting solar eruptions. Physicists like Berger and researchers at the Space Weather Prediction Center can currently predict solar eruptions, but with what meteorologists would consider fairly lousy accuracy and detail compared to 10-day forecast of sunshine and rain.
“We can tell you when the coronal mass ejection will hit, roughly, plus or minus 10 hours,” Berger explains, “But we don’t have a good way to forecast what is going to happen in the low-Earth orbit environment.” In other words, it’s tough to say how much a geomagnetic storm will affect the operation and trajectory of satellites and regular electrical operations on the ground.
The sticking point for better forecasts is that while NOAA runs an ongoing simulation of the Earth’s upper atmosphere, that model isn’t yet able to assimilate real-time data the way terrestrial weather forecast models can. “That is a research program that will take several years to come to fruition,” Berger says.
In the meantime, the sun will keep climbing toward solar maximum in 2025. But even after that peak, it doesn’t mean satellites and astronauts are out of the woods as far as solar storms are concerned. “Really any time between now and 2028 or 2029, we could potentially get a large eruption beginning to hit the Earth,” Berger says. That probably won’t affect daily life, but NASA and satellite operators will need to keep an eye toward the sun.