Life on Earth wouldn’t exist without the Sun. Its light is the energy that powers so much of our planet, from photosynthesis to changes in the atmosphere. However, like everything else in the universe, the Sun is not static – it changes. Its better-known cycle lasts around 11 years and is marked by a period of intense activity, dramatic ejection of plasma, and energetic eruptions such as solar flares. 

Solar flares can often mess up our technology and historically, have caused massive damage, as well as spectacular aurorae. In a world relying more and more on tech, the big question we have is: are we ready for the next massive solar flare? For The Big Questions, IFLScience’s podcast, we spoke to Dr Ryan French, solar physicist at the National Solar Observatory and author of The Sun: Beginner's Guide to Our Local Star, to find out the answer.

What is a solar flare?

Ryan French (RF): A solar flare is essentially a release or a conversion of energy in the atmosphere of the Sun. Far away from the nuclear fusion that dominates in its center, in the atmosphere, everything is dominated by magnetic fields. Solar flares, eruptions, sunspots – any of these fun processes you might have heard about on the Sun – are all to do with magnetic fields. 

In the case of solar flares, they occur when you have a build-up of energy within magnetic fields that want to relax. They want to get rid of this energy, but they can’t; if you continue to build up this energy enough, these magnetic field lines break. As this happens, that energy is released from the magnetic fields to the heating of plasma, light, and the acceleration of particles, and that is what we see as a solar flare, reaching us at the speed of light.

Fundamentally, the solar cycle is just a cycle of magnetic complexity in the atmosphere of the Sun.

Solar flares are associated about half of the time with what we call coronal mass ejections, which are eruptions of plasma from the Sun. These are different and they only correlate about half of the time; you can have flares without eruptions, and you can have eruptions without flares. Eruptions travel a lot slower, taking around 12 to 36 hours to reach us here on Earth.

How often do solar flares happen?

(RF): The short answer is pretty much all the time. The longer answer is that it depends on how big of a solar flare you are talking about. We have different categories of solar flares: the largest category is what we call an "X"-class solar flare; below that is an ‘M'-class, which can be thought of as midclass; and below that you have ‘C’, ‘B’, and ‘A’ classes. 

The other thing to consider is that the Sun follows a cycle of how often these flares occur, an 11-year cycle of increasing and decreasing activity. Towards the peak of this solar cycle, which we call the solar maximum, we have solar flares every day: C-class every day; M-class every week, and maybe an X-class flare once a month or so. 

At the solar minimum, flares don’t happen for months at a time, at least not to any observable level. What we believe is that if we keep going smaller and smaller, below levels that we can actually observe, there still are solar flares happening down there – they’re just too small for us to observe currently.

We are currently approaching a solar maximum. Is there an uptake of all kinds of energetic activity on the Sun, not just solar flares?

(RF): Yes – there’s an increase in everything. Fundamentally, the solar cycle is just a cycle of magnetic complexity in the atmosphere of the Sun. If you have a lot of complex, concentrated magnetic fields, they interact a lot more and they release energy a lot more. This means that not only do we get more flares, but we also get more eruptions, and a lot more sunspots too. We also get a lot more quiet Sun eruptions as well, which are eruptions that don’t occur over sunspots. 

So, everything is picking up at the moment and we expect the maximum to occur sometime between next year and 2026.

You mentioned X-class flares, which are the most powerful. How bad do they get? How powerful is the most powerful that we have on record?

(RF): It’s worth noting that X-class flares are the largest category of flares. Unlike an M-class flare, where the top cap of an M-class is the bottom of an X-class, with an X-class, there is no cap. We can have what we call an X1-class flare, or we can have X10-class flares, or even X50-class flares. 

The biggest solar flare we’ve had since we’ve been able to measure them directly from space is something like an X28-class flare, back in 2003. The largest flare we have on human record occurred long before we had telescopes in space, way back in 1859. It’s quite a famous flare, called the Carrington Event, named after Richard Carrington, who was – a great job combination – a part-time astronomer and a part-time brewery owner. The dream!

Can you tell us more about the Carrington Event?

(RF): Carrington would observe the Sun every day and one day he saw a bright light in a little sunspot that he had been observing – and it wasn’t a flash. He saw it slowly brightening over tens of seconds and slowly decay over minutes. We now know that this was a solar flare, because that evening, the aurora borealis, or the Northern Lights, was seen all the way down to the tropics. It was seen in the South of France and all the way to Florida.

Telegraph machines, which were the peak of technology at the time, were also acting really strange. They were giving electric shocks to operators and sending messages without being plugged into a power source.

Potentially, up to one in five satellites could break and stop working.

We don’t really have an estimate we have for how big of an X-class the Carrington Event was, but it was a lot bigger than anything observed in recent years and triggered a very powerful eruption. As that eruption of plasma moved through the solar system towards the Earth, it carried with it a very concentrated magnetic field. 

If you change a magnetic field over a conducted material, you induce an electrical current. If you start inducing electrical currents over things that already have a current, you’re going to start overloading the system, you’re going to give electric shocks, and you’re going to break stuff. That’s basically what happened back in 1859. Now, if that happened today, it would be a very different kind of story – clearly, we have far superior technology than just telegraph machines.

Let's imagine we got a solar flare that powerful today and it’s not just electrical cables that are affected – it’s pretty much every way we shape our modern lives, with radio and satellite communication. What would happen?

(RF): We consider that to be the worst-case scenario. This is the scenario that we prep for and that is listed in government risk registers. Potentially, up to one in five satellites could break and stop working. Some of them might be able to get back online, but a large number of satellites could possibly lose connection permanently. 

Down on the ground, there would be a temporary loss – for maybe a couple of days – of radio communication. Radio waves work by bouncing off the upper atmosphere; solar flares cause an expansion of this region, meaning radio waves can’t propagate as normal. This would prevent communication with airlines, and with ships, so flights would be grounded for a few days, or maybe even a week. GPS satellite navigation would also be affected.

Perhaps the biggest concern is power grids. Not all power grids are at risk; the ones most threatened are those that are very centralized, generating their electricity in one place and transporting it over long distances. If you have a very localized, decentralized power grid, then you are less at risk but if your systems are older, you could have a loss of transformers. This could cause power outages in certain regions of the world, maybe for a couple of weeks until the transformers can be replaced. 

Long story short, no one physically or health-wise is at risk from these events. It’s also not going to send us back to the Stone Age, unlike some quotes you might have seen. It’s not going to fry your phone for instance, but the larger electronics are at risk. Current estimates suggest it would cause similar amounts of financial damage to any other natural disaster. 

A solar flare almost caused the end of the world.

It’s also a spectrum; on one end of the spectrum, we expect a worst-case scenario event to happen perhaps every 200 years. On the less powerful end, satellite operators or the military will care about even the small events that happen a lot more often, sometimes every few weeks. As members of the general population, we don’t really notice those day-to-day.

Can you give us a few examples of stronger solar flares that have disrupted technology in recent years?

(RF): There have been a few cases of middle-sized events in recent decades that have affected everyday life. A very recent example happened last year when Elon Musk and SpaceX launched some Starlink satellites. Forty were lost because there was a solar flare; it expanded the atmosphere slightly, which caused the satellites to experience a powerful amount of drag.

Back in 1989, a hydroelectric plant on the East Coast of Canada lost power for about 13 hours because of an eruption from the Sun, causing millions of people to be without electricity. There were a few other cases like that in recent decades too, and a really interesting one happened back in 1967 when a solar flare almost caused the end of the world. 

It was the height of the Cold War, and a US naval ship lost communication with the rest of the network. Their first thought was, “This must be an attack, we should get ready for a counterstrike”, and the story goes there was one guy on board who knew about solar flares and space weather. He said something along the lines of, “Hang on, let’s just check before we react. Let’s just check that this isn’t the Sun.” 

They made some phone calls and as we know now, there had been a massive solar flare and that was the reason for that communication outage, not the alternative. So, it’s important that we understand solar flares, and can mitigate their impact.

If there is a massive solar flare, what are we going to do? What are the contingency plans that are in place to keep us and our technology safe?

(RF): The last 10 years in particular, there has been massive investment in understanding solar flares, the eruptions that are associated with them, and their impact here on Earth. There are two organizations that are monitoring the Sun 24 hours a day, seven days a week. Just like regular weather forecasters, there are space weather forecasters – people sitting behind a desk watching the Sun, waiting for it to do anything. 

When it comes to the success rate of forecasting events on the Sun, we’re probably where we were with regular weather 50 years ago.

The United Kingdom has one of those two groups at the Met Office, famous for regular weather forecasting. There is one in the US as well and the US military does something similar too, but that’s not as publicly accessible. If these space weather forecasters see anything happening, or even if they don’t see anything happening, they send daily alerts to airlines, satellite operators, and the military.

You also probably wouldn’t organize something very sensitive military-wise if there was a large solar flare coming, as that might damage radio communications. You wouldn’t launch some satellites into space, like SpaceX did, if there was a large solar flare that had just happened, for example. 

Currently, when it comes to the success rate of forecasting events on the Sun, we’re probably where we were with regular weather 50 years ago, so it’s still got a long way to go. We can’t specifically forecast when a solar flare will occur. We can give probabilistic forecasts of when they will happen, but more importantly, after that flare has happened, we can check to see if that flare has caused an eruption. 

It’s the eruption that causes the most damage to power grids and satellites, and we model those eruptions to see if it’s going to be directed toward Earth and what we think the impact might be from that. If there is anything really severe – which hasn’t happened yet, since these forecasts have been going – the plan essentially is to turn off the power grid manually. 

It sounds strange – why would you turn off the power grid manually? If you remember, the damage comes from this magnetic field that’s created by the interaction from the eruption with the Earth’s magnetic field, which generates a current. The damage comes when you have electrical currents that are conflicting with the electrical currents that are already in those power grids or those satellites; that’s what breaks the stuff. 

If you turn off the system, let the electricity get generated and pass through, and wait for everything to pass, then you can turn it back on again and mitigate that damage. So, there are preventative things that we can do if something really bad looks like it’s going to come to us.

Another part is future research; we are always trying to improve models and improve our understanding of solar flares. It’s not the same scenario it would have been 20 years ago if one of these large events happened.

We’re currently living in a great time to research the Sun…the golden age of solar physics.

What are we doing to better understand our star and how it affects the interplanetary space around Earth?

(RF): There are a whole bunch of scientists working on different things. I work on solar flares, so I am trying to understand the processes that happen on a very small scale that trigger a solar flare and eruption. We have a large suite of telescopes both on the ground and in space that can do this. 

There are other people who look at how an eruption, once it’s triggered, moves into the solar atmosphere, and how it evolves as it travels through space. Others look at what happens when it arrives on Earth. So, there are lots of different parts of these systems that are being worked on by different scientists, and hopefully, some, if not all those parts of that system, will be put together incrementally to improve the models that we do have. 

At the moment, we can’t say when a flare will occur; but if we can fully understand what triggers a solar flare maybe one day, we will be able to say that. We’re currently living in a great time to research the Sun. It’s been called, informally, the golden age of solar physics. 

We have a bunch of different telescopes. Back in 2018, NASA launched the Parker Solar Probe, which is a spacecraft that orbits the Sun in a very elliptical orbit, getting as far as 95 percent of the way to the Sun. It flies through its atmosphere, measuring eruptions as they launch off the Sun. We also have the European Space Agency’s Solar Orbiter spacecraft which is also orbiting the Sun with telescopes, looking at the Sun from different angles. Again, it gives a great perspective on how eruptions are triggered and evolve. 

The National Science Foundation in the US has built a telescope called the Inouye Solar Telescope, which is 4 meters [13 feet] wide. That might seem small compared to some of the night sky telescopes, but think about how bright the Sun is, and how much light you’re covering from a 4-meter photon bucket. 

Expect some very exciting results to come from that telescope and coordination between all these instruments in the next few years – it’s a very exciting time to research the Sun.

This interview was part of IFLScience's The Big Questions and has been edited for length and clarity. Subscribe to our newsletter so you don’t miss out on the biggest stories each week.