A top Sun researcher explains what kind of trouble solar flares might cause
The Sun is the ultimate source of nearly all energy on Earth, but it also poses a threat. Every now and then, our local star belches out a jet of energy powerful enough to knock important technology offline.
Here's the scary part: Earth hasn't been struck by exceptionally powerful space weather since we've come to rely on complex technology for nearly every facet of day-to-day life. As the Sun approaches a time of maximum activity, that's causing some people to be concerned about what dangers might be in store.
In fact, experts who keep an eye on space weather say we've experienced a few low-level events over the last several months. So, Interesting Engineering sat down with heliophysicist Gregory D. Fleishman, an expert in the Sun's outer layers, to learn more about what kind of trouble the star might cause.
This interview was edited for length and clarity.
Interesting Engineering: What is space weather?
Gregory D. Fleishman: It's a sort of general term that describes all sorts of conditions in interplanetary space that affect infrastructure, technology, and life on the Earth. There are a number of different ingredients forming space weather. There is a ground state, which is basically solar wind. Solar wind itself is not uniform. It's a flow of plasma flowing from the Sun outwards. It's not exactly a steady-state. It's a persistent phenomenon. There are two main sorts of solar wind: fast solar wind and slow solar wind, depending on the velocity of this plasma.
IE: That's happening all the time. What kind of processes happen only occasionally?
Fleishman: Then, on top of this ground state, there are a lot of perturbations. This perturbation can be co-rotating structures, co-rotating interaction regions, or CIR for short. There are ejections, like coronal mass ejections, which became interplanetary coronal mass ejections, which are ejections of bubbles of plasma, magnetized plasma.
On top of that, another important ingredient of space weather is energetic charged particles, which can be produced either in the Sun (mainly by solar flares) or they also can be produced by propagating shockwaves associated with coronal mass ejections.
Finally, there's the radiation itself, the electromagnetic waves produced on top of the background of solar radiation. The electromagnetic waves associated with these solar flares occupy a very broad electromagnetic range, from radio waves all the way up to X-rays and gamma rays.
IE: What does all of this mean for life on Earth?
Fleishman: All of these ingredients generate their own physical effects and eventually their own issues or problems for either technology and infrastructure or the health of astronauts. For example, if you have strong radio bursts — especially if the radio bursts are strong and polarized — they can quench all GPS navigation systems on the sunlit part of the Earth. Of course, this is highly important and potentially harmful because you want to have this navigation system working 24/7. If it's disrupted, even for 15 minutes, for example, that typical duration of a flare of a radio burst, it does not work.
IE: What would happen if a burst were to hit, for example, New York City?
Fleishman: Suppose that we lived on the Moon, which does not have an atmosphere or a magnetic field. Then such bubbles directed toward the Moon will hit it. If New York City were there, it would destroy New York City if it were big enough. The lunar surface is characterized by craters. This is because there is no protective shield there.
IE: But on Earth, we have a protective shield, right?
Fleishman: We have two sorts of protective shields protecting the Earth. There's the atmosphere, so meteors that enter the atmosphere just burn up. Maybe even more important from this perspective, we have the terrestrial magnetic field, which protects us from the direct impact of charged particles from the Sun or from galactic cosmic rays. The magnetic field just shields the Earth from direct hits from these particles. The charged particles just rotate around magnetic field lines, and they can only propagate toward the poles or be trapped in the radiation belts.
The magnetic field also offers protection from coronal mass ejections. Those are also magnetized bubbles. They hit and interact with Earth's magnetic field. When this happens, a lot of very interesting physical processes take place, in particular sandstorms, but there is no direct impact of the huge bubbles on New York City, for example. It's distributed all over the planet and shielded by the atmosphere and the magnetic field.
IE: In 1859, a solar storm hit Earth and caused a lot of problems. What happened exactly, and how might things be different if something similar were to happen now?
Fleishman: This is a very famous event. As far as I know, the only technological system affected was the telegraph. What happens is when you have this electromagnetic field, you induce electric currents in the wires. Just as in a laboratory, you apply electromagnetic fields and use electric current. The stronger the electromagnetic field, the stronger the electric current. The electric current in the wires generates heat, in particular, if it's too much. If it's more than planned for the wire, you can burn out equipment. This is very serious. If we had a similar event right now, a lot more technological systems would be affected. Simplistically speaking, all modern technological systems that rely on electromagnetic fields or electromagnetic waves will — or could — be affected somehow.
IE: Most of the ejections from the Sun don't end up hitting Earth, right? How often should we expect one of these events to come our way?
Fleishman: So, it's also a question of statistics, yes? So if during solar maximum years, we have a couple or a few ejections per day and each ejection has an opening angle of, say, 20 or 30 degrees, then you can easily compute that roughly five percent or ten percent of all ejections will hit the Earth. Most ejections don't come from the Sun's polar regions. They come from active regions located roughly plus or minus 20 degrees from the solar equator. This implies that each tenth or twentieth ejection will hit the Earth or Earth's magnetosphere.
More important than that, we have a huge fleet of satellites, and many of them are located far away from Earth in different directions from the Sun. Even events that do not hit the Earth can hit one of the satellites. It's a persistent problem. The engineers who produce the equipment and technology for satellites have to think about those potential impacts.
IE: These events happen more often sometimes and less often sometimes. What does that pattern look like?
Fleishman: We observe a roughly 11-year period where the number of sunspots, or active regions, experiences minima and maxima. It's said to oscillate, but it's not oscillation exactly. It's variation. Sometimes cycles are shorter or longer. After one cycle is over, then a new cycle begins, and you can observe more and more active regions on the solar surface. Proportionally, you'll observe more and more events of solar activity, which can be flares, jets, or eruptions like solar mass ejections. It's roughly proportional to the number of sunspots.
If you have just one active region or sunspot, and it has a 10 percent probability of eruption, then you might have one, or you might not. If you have hundreds of active regions with the same 10 percent probability, then you will have at least 10 active regions that will generate activity. This is how it works at the maximum, which is expected around 2025. We'll probably have many active regions, some of them flare-productive and others not. All indices of solar activity will go up proportionally.
IE: Why do some sunspots lead to these ejections?
Fleishman: When we're talking about a single sunspot, this means a dark area where the temperature of the plasma, or gas, is lower than around it. Why is this temperature lower? Because the magnetic field is stronger than outside. It's strong enough to inhibit the plasma. This means that heat transfer from below to the surface is somewhat suppressed. With less heat, the final temperature is lower. So, these dark areas are indications of a strong magnetic field area.
IE: So the sunspot is a symptom of a deeper process that sometimes causes the other phenomena?
Fleishman: Yes. Typically, if you have just an isolated sunspot, there probably won't be too much flare production because it won't accumulate sufficient free magnetic energy. Free magnetic energy is the energy that can be released. You have to have electric currents supporting this free magnetic field. These manifest themselves in structures, which can be sigmoidal flux tubes or curved structures, or something that looks like shared motion. For example, when negative and positive magnetic fields come into close contact and shift relative to each other, you have a lot of stress and a lot of tension. This contains a lot of free energy. To have this situation, you need areas of positive magnetism and negative magnetism.
Simplistically speaking, you have to have two sunspots, one with a positive magnetic field and the other with a negative magnetic field. If they are in close contact, you have a lot of structures and indications of free energy. Then, when it's tangled and complex enough, an eruption happens because the system loses stability.