When the Sun moves, the sky lights up and, in complete darkness, green, pink or bluish streaks appear - the Northern Lights. In 2024, when the immense star is due to enter a peak of activity, these nocturnal spectacles could multiply above our heads.
150 million kilometers from Earth, the Sun still appears to be its usual form from a distance: a large ball of gas that dazzles and heats the atmosphere. But, in reality, its activity becomes more or less intense during a cycle which lasts approximately eleven years. However, according to specialists, notably those from the American Oceanic and Atmospheric Observation Agency (NOAA), the Sun is currently approaching the peak of activity of its current cycle, which started in 2019.
“The Sun is an enormous ball of extremely hot plasma, composed of electrically charged particles, in rotation, linked to a magnetic field,” explains Pierdavide Coïsson, assistant physicist at the Globe physics institute in Paris. “In a very complex dynamic, it works like a magnet and with each new cycle, it changes direction. And this is accompanied by an increase in its activity.”
In other words, at the start of the cycle, everything is more or less calm in the sun, the magnetic North and South poles are in place. But, gradually, the magnetic field is disturbed. It winds, loops... until the initial North and South poles find themselves reversed.
“A boiling pot”
If researchers struggle to explain the exact process behind this phenomenon, the symptoms are always the same: “With magnetic instability, the surface of the Sun is covered with spots. It looks like a boiling pot,” continues Pierdavide Coïsson.
In February 2021, the European Space Agency (ESA) took an image of the Sun using its Solar Orbiter probe. The surface of the star then appears homogeneous, smooth, and the activity is low. Two years later, in October 2023, a second photo shows the Sun with large identifiable spots - a sign of peak activity.
“These are the centers of what we call solar flares,” explains Frédéric Pitout, assistant astronomer at the Institute for Research in Astrophysics and Planetology (Irap). “Electric particles and matter – called coronal mass – will be ejected into space at high speed.”
Most of the time, these solar flares have no impact on Earth: the elements released into space are sent in another direction or the flare is too weak to be seen as far as the blue planet.
But as we enter the Sun's peak activity, the risk of seeing significant solar flares increases. On Sunday March 24, the Space Weather Prediction Center (SWPC), an American agency specializing in observing solar activity, recorded a class X1.1 eruption, among the most powerful. A few weeks earlier, on February 23, the ESA had recorded an even larger class X6.3 eruption.
A very active region of the Sun recently triggered three X-class solar flares, which are the most powerful.
The largest, an “X6.3” flare that occurred at 11:43 p.m. CET last night, is the strongest solar flare ever observed during the solar cycle… pic.twitter.com/uMusU443Cx
— ESA France (@ESA_fr) February 23, 2024
The magnetosphere shield
“And sometimes, the ejections will be sent directly into the exact alignment of the Earth and have an impact,” continues Pierdavide Coïsson. However, these do not directly affect each other. They first collide with the magnetosphere, a sort of invisible shield generated by the Earth's magnetic field.
“The magnetosphere allows some of the elements to be deflected, but electrical particles can still manage to break through this defensive line and open the door to our atmosphere,” he continues. We will then speak of a “solar storm” or geomagnetic storm.
“The majority of the time, the particles will simply head primarily towards the polar zones and give rise to the northern and southern lights,” adds the specialist. “But the more powerful the phenomenon, the more the auroras will descend in latitude.” These nocturnal shows are therefore the result of the interaction between solar particles and the earth's atmosphere. And when the Northern Lights are visible as far away as Europe, it is the sign, originally, of a major solar eruption.
An aurora borealis appears around the Arctic Circle near Rovaniemi, Finland, on March 23, 2023. © Alexander Kuznetsov, AFP
Risks for our infrastructure
But behind the visual delight caused by the Northern Lights, the Sun's activities can also hide potential problems for our electrical infrastructure and the satellites orbiting the Earth.
“Beyond the luminous aspect, the particles ejected from the Sun above all transport a lot of energy. In the event of a particularly intense solar storm, they can therefore disrupt all electrical networks,” insists the specialist.
The strongest example of this phenomenon dates back to 1859 and the Carrington event – named after the British astronomer who studied it. In the middle of the 19th century, the entire telegraph network was disrupted by the fire of telecommunications stations due to surges on the electrical network. A sign of the importance of this solar storm, the Northern Lights could be seen as far away as Cuba.
But unlike in 1859, the world today is meshed with electrical conductors - high-voltage lines, catenaries, rails, pipelines, pipes - making the global electricity grid particularly sensitive to the effects of solar storms. “More recently, in March 1989, a major solar flare caused the total collapse of Quebec's electricity network for 9 hours,” adds the specialist. "And in October 2003, 'the Halloween solar storm' caused power outages and problems in telecommunications networks in several parts of the world, notably in Japan and the United States."
And the risks from solar storms also lie right above our heads. “There are also risks for all satellites in Earth orbit,” continues the specialist. “Energetic particles can disrupt their electronic system.” In 2022, Starlink, Elon Musk's company which develops satellite Internet, lost around forty devices just after a launch, while they were in the deployment phase, due to a solar flare .
“But satellites have become essential to our daily lives. They, for example, make it possible to use GPS to locate planes or boats. They are also the ones that make long-distance communications possible,” adds Frédéric Pitout, from Iraq. “If they suddenly fail, even for a few minutes, it could have catastrophic consequences.”
This specialist also thinks about the implications in space research. If the astronauts who operate in the International Space Station are protected by the magnetosphere, it will not be the same for those who leave for the Moon or, in a more distant future, for Mars.
Space weather
According to a 2003 OECD study, a similar event at Carrington is considered one of the worst phenomena that could happen today with damage whose global cost is estimated at several trillion dollars. A return to normal would take months, if not years.
This threat has driven the development of “space weather” for several years. Using ground-based observatories and a fleet of space probes constantly observing the star, researchers are trying to spot flares and warn if a major one is approaching. “But it is still very difficult to anticipate,” warns Frédéric Pitout. “When we see the eruption, we already have only a few hours or a few days before we see the potential effects.”
The ESA Space Weather Services Network, managed by the ESA Space Security Programme, is the main dedicated infrastructure in Europe. Although it has a series of terrestrial sensors, the organization is also working on the development of space missions such as Vigil. With one goal: to provide near real-time data on solar activity before it is detectable from Earth.
Today marks #SolarOrbiter's closest approach to the Sun, giving it a front-row seat during #SolarEclipse2024 🕶️🍿
What's more, this weekend the spacecraft is 90 degrees further round the Sun compared to Earth, meaning it can watch for potentially dangerous eruptions sent in our… pic.twitter.com/4CZrC52r21
— ESA's Solar Orbiter (@ESASolarOrbiter) April 4, 2024
“In any case, there remain many mysteries to be unraveled around the solar wind but also the functioning of this solar cycle and this inevitably causes many uncertainties,” adds Pierdavide Coïsson. “Fortunately, a magnetic storm remains a rare phenomenon even if the Sun is at its most active.”
For their part, “electricity companies are all working to make their networks less vulnerable,” concludes Frédéric Pitout. “Airlines also closely monitor solar activity to protect themselves and readjust route maps in the event of risks.” Once the year 2024 has passed, however, specialists should be able to take advantage of a lull of another eleven years to prepare for the next peak of solar activity.
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