5.01.2026

In May 2024, the strongest solar storm in twenty years raged. An international team led by ETH Zurich observed it. Their findings are now helping to improve space weather forecasts. 

The European space probe Solar Orbiter delivers images of the sun, including observations of what is, from our perspective, its far side.  (Image: ESA / AOES)

Our sun rotates around its axis once every 28 days. From earth, therefore, active regions of the sun can only be observed for up to two weeks at a time. After this, they rotate beyond our field of view, remaining hidden from us for two weeks. “Fortunately, the Solar Orbiter mission, launched by the European Space Agency (ESA) in 2020, has broadened our perspective,” says Ioannis Kontogiannis, solar physicist at ETH Zurich and the external page Istituto ricerche solari Aldo e Cele Daccò (IRSOL) in Locarno.

The Solar Orbiter spacecraft orbits the sun once every six months, also observing its far side. Between April and July 2024, it was able to monitor one of the most active regions in the last twenty years. In May 2024, the region known as NOAA 13664 rotated to the side of the sun facing us, triggering the strongest geomagnetic storms on Earth since 2003. “This region caused the spectacular aurora borealis that was visible as far south as Switzerland,” says Louise Harra, professor at ETH Zurich and director of the Davos Physical Meteorological Observatory.

Data from two space probes combined

To better understand the formation, development and effects of such superactive regions on the sun, Harra and Kontogiannis brought together an international team of researchers. This team combined the data collected by NOAA 13664’s Solar Orbiter on the far side of the sun with data from NASA’s Solar Dynamics Observatory spacecraft, which is located on the earth–sun line and observes the near side.

This allowed the group to track region NOAA 13664 almost continuously for 94 days. “This is the longest continuous series of images ever created for a single active region: it’s a milestone in solar physics,” says Kontogiannis. The team observed the birth of NOAA 13664 on 16 April 2024 on the far side of the sun, as well as all the changes that the active region underwent until its decay after 18 July 2024. 

Complex magnetic fields causing solar storms

Strong and complex magnetic fields prevail in the active regions of the sun. They occur when strongly magnetised plasma reaches the sun’s surface, and they often cause violent eruptions. These solar storms emit enormous amounts of electromagnetic radiation, known as flares, and eject plasma from the sun’s atmosphere as well as high-energy particles into space. 

In addition to auroras, solar storms can also cause significant damage to our high-tech world. They can cause power outages on earth, disrupt communication signals, expose aircraft crews to increased radiation or cause satellites to crash, as happened in February 2022, when 38 of 49 Starlink satellites belonging to US space company SpaceX were lost within two days of their launch. 

Unnerving effects 

“Even signals on railway lines can be affected and switch from red to green or vice versa,” says Harra. “That’s really scary.” NOAA 13664 also had caused problems in May 2024. “Modern digital agriculture was particularly affected,” says the scientist. “Signals from satellites, drones and sensors were disrupted, causing farmers to lose working days and leading to crop failures with considerable economic losses.”

“It’s a good reminder that the sun is the only star that influences our activities,” adds Kontogiannis. “We live with this star, so it’s really important we observe it and try to understand how it works and how it affects our environment.”

Thanks to data from space probes, researchers were able to track three solar rotations for the first time ever, observing how the magnetic field of a superactive region developed over several episodes, becoming increasingly complex. Ultimately, an intertwined magnetic structure was formed, before the strongest flare in the past twenty years was released on the far side of the sun on 20 May 2024. 

Weather forecasts in space

It is hoped that these observations will contribute to a better understanding of solar storms and their potential impact on earth. The aim is to improve the accuracy of space weather forecasts, so that sensitive modern technology can be better protected. “When we see a region on the sun with an extremely complex magnetic field, we can assume that there is a large amount of energy there that will have to be released as solar storms,” explains Harra.

Currently, however, researchers are unable to predict how large an eruption will be, whether there will be one strong eruption or several weaker ones, and when these might occur. “We’re not there yet. But we’re currently developing a new space probe at ESA called Vigil which will be dedicated exclusively to improving our understanding of space weather,” says the scientist. The mission is planned for launch in 2031.

Quelle: ETH Eidgenössische Technische Hochschule Zürich