Could the Sun Fry Earth with a Superflare?

Scientific American

02-05-2025

In our daily lives, the sun seems constant and quiet, sedately shining at a steady pace. But looks can be deceiving: our star can also blast out powerful solar storms, huge explosions of energy and subatomic particles. If these are directed toward us, they can trigger auroras and disrupt our power grids, as well as play havoc with Earth-orbiting satellites.
These storms are magnetic in nature. A fundamental rule in physics is that charged particles create magnetic fields around them as they move. And the sun is brimming with charged particles because its interior is so hot that atoms there are stripped of one or more electrons, forming what we call a plasma. The superhot plasma closer to the core rises, whereas cooler plasma near the surface sinks, creating towering columns of convecting material by the millions, each carrying its own magnetic field. These fields can become entangled near the surface, sometimes snapping—like a spring under too much strain—to release enormous amounts of energy in a single intense explosion at a small spot on the sun. This sudden flash of light accompanied by a colossal burst of subatomic particles is called a solar flare.
The most powerful flare we've ever directly measured occurred in 2003, and it emitted about 7 × 10 25 joules of energy in the span of a few hours. That's roughly the amount of energy the whole sun emits in one fifth of a second, which may not sound very impressive—until you remember it comes from just a tiny, isolated region on the sun's surface!
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We also know that, historically, our star has spat out much bigger flares. High-speed subatomic particles raining down from solar storms slam into the nitrogen in our atmosphere to create an isotope called beryllium 10, or Be-10, which can be captured in polar ice after falling to Earth's surface. By examining ancient ice cores, scientists are able to obtain accurate dates for spikes in Be-10 (and other related isotopes), which can then be used to track historic solar activity.
Such isotopic spikes have revealed what may be the most powerful solar eruption in relatively recent history, an event that occurred in 7176 B.C.E. Scientists argued at first about the cause of these spikes; the sun's activity didn't seem powerful enough to create the amounts of isotopes seen. Supernovae or gamma-ray bursts could explain the spikes, too—but only by occurring rather close to our planet, and that should've left behind other forms of evidence that, so far, scientists haven't found. Consequently, the current consensus is that the sun is indeed responsible for these massive upticks in isotopes. Scientists now call these spikes ' Miyake events,' in honor of Japanese cosmic-ray physicist Fusa Miyake, a leader in discovering and understanding them.
While these flares were huge, there are reasons to suspect the sun is capable of unleashing even bigger ones. Some stars undergo what are called superflares, which are ridiculously powerful, reaching a total energy of 10 29 joules, or the equivalent of what the sun emits over the course of 20 minutes. In more human terms, that's about 300 million years' worth of our global civilization's current annual energy usage—all squeezed into a brief burst of stellar activity.
Superflares are relatively rare. Observing them in any given star would take a stroke of luck—unless you stack the odds in your favor.
That's just what an international team of astronomers did. The Kepler spacecraft monitored about half a million stars over a period of a decade, looking for telltale signs of accompanying planets. But all those data can be used for other things, too. The astronomers looked for superflares arising from more than 56,000 sunlike stars in Kepler's observations—which added up to a remarkable 220,000 total observed years of stellar activity. The researchers published the results in Science in late 2024.
By sifting through that vast dataset, the team found 2,889 likely superflares on 2,527 sunlike stars. That works out to roughly one superflare per sunlike star per century, which seems pretty terrifying because it would presumably mean the sun sends out an explosive superflare every hundred years or so.
But let's not be so hasty. For one thing, a star's rotation can powerfully influence the development of flare-spewing magnetic fields, and the rotational period was unknown for 40,000 of the study's examined stars—so it's possible this part of the sample isn't representative of the actual sun. And 30 percent of the superflare-producing stars were in binary systems with a stellar companion, which could also affect the results. The list of potential confounding variables doesn't stop here—there are several other factors that might make a seemingly sunlike star more prone to producing superflares than our own sun is.
Then again, as I already mentioned, Be-10 and other telltale isotopes can be produced in other ways that don't involve stellar flares. And, for that matter, it's not at all clear how well superflares would specifically make such particles. So although we've counted five sun-attributed Be-10 spikes across the last 10,000 years, that doesn't mean the sun has only produced that many strong flares in that time. Perhaps there were others that left more subtle, as-yet-unidentified records in the ice—or that weren't aimed at Earth and therefore produced no terrestrial isotopic signal at all.
If the sun did blow off a superflare today, what would be the effects? The impacts to life on Earth would probably be pretty minimal; our planet's magnetic field acts as a shield against incoming subatomic particles, and our atmosphere would absorb most of the associated high-energy electromagnetic radiation (such as gamma and x-rays).
Our technological civilization is another matter, though. A huge flare could fry the electronics on all but the most protected satellites and disrupt power grids to cause widespread and long-lasting blackouts. Engineers have devised safeguards to prevent damaging electrical surges from most instances of extreme space weather, but if a flare is powerful enough, there may not be much we could do to avoid severe damage.
Should we worry? The takeaway from the study is that it's possible the sun produces superflares more often than we previously thought, but this conclusion is not conclusive. So consider this research a good start—and a good argument for getting more and better information. Don't panic just yet!