The phenomenon was expected, hoped for by some and feared by others. As the Sun's 11-year activity cycle neared its maximum, an explosion on its surface triggered a solar storm of a magnitude not seen for over 20 years.
The spectacular consequences of this phenomenon were visible on the night of Friday, May 10, in the form of northern lights at exceptionally low latitudes. Particles, ejected during these eruptions 150 million kilometers from Earth, ionize the upper layers of the Earth's atmosphere, under the effect of the magnetic field, to cause these astonishing diaphanous colors in the sky. These aurora borealis were seen in Europe and in France, even in the Paris region. Numerous photos of these exceptional phenomena were posted on social media by amazed enthusiasts.
Mes aurores boréales à Charenton-le-Pont (Paris) ???????? pic.twitter.com/PAuhixzttE
— Simon ???? (@Reelwens) May 10, 2024
BREAKING: Thousands of reports of Northern Lights coming in from multiple locations across Europe. A severe G4 geomagnetic storm is currently affecting Earth. Truly the most stunning aurora show in years. Currently visible as far south as northern Italy. pic.twitter.com/S3uvGCxiHe
— Nahel Belgherze (@WxNB_) May 10, 2024
NASA had already announced on May 9 that it was expecting such events, after observing these explosions on the Sun's surface. The eruptions eject immense quantities of matter from the star, which then disperse. These coronal mass ejections – at least seven of which have been observed heading toward the Earth – originate from a sunspot around 17 times the diameter of the Earth. They travel at several hundred kilometers per second.
Other, less aesthetic consequences of such an event are possible. On Friday evening, the US National Oceanic and Atmospheric Administration announced that it had observed conditions associated with a level 5 geomagnetic storm, the maximum level on the scale used. In other words, satellite and ground communications networks, navigation systems such as GPS and radio broadcasts may be disrupted.
Earlier this week, NASA alerted communications satellite and power grid operators in North America to the risk of disruptions. These (none were reported as yet on Saturday morning) may continue for several days. Like the northern lights, the effects of this solar storm have yet to reach the Blue Planet.
The last event to reach level 5 was the "Halloween storms" of October 2003. At the time, power cuts occurred in Sweden, and transformers were damaged in South Africa.
Solar cycle 25, which began in December 2019, was expected to peak in 2025 but was not anticipated as an exceptional peak. Our star's breaths are not regular. However, as early as the end of 2023, the agitation observed by the Sun's observation satellites enabled astronomers to announce that the peak of cycle 25 would be stronger than expected and would undoubtedly occur earlier. At the time, they were talking about the second half of 2024. It's too early to say whether this event is a precursor to the next peak in activity, or whether it marks the peak before the ebb.
Translation of an original article published in French on lemonde.fr; the publisher may only be liable for the French version.