Scientists pinpoint how the Sun unleashes electron storms

The Sun shapes life on Earth in countless ways. Beyond its warmth and light, it also hurls a constant stream of energetic particles into space. These solar particles can disrupt satellites, threaten astronauts, and influence space weather. Until recently, their origin remained only partly understood.

Now, the European Space Agency’s Solar Orbiter mission has revealed a breakthrough. The spacecraft has traced energetic electrons back to two distinct sources on the Sun, uncovering fresh details about how our star unleashes its power.

Distinct solar electron storms

The Sun accelerates electrons to nearly light speed and sends them racing across the Solar System. Scientists call them Solar Energetic Electrons (SEEs). Using Solar Orbiter, researchers separated them into two groups: those linked to solar flares and those tied to coronal mass ejections, or CMEs.

Study lead author Alexander Warmuth is a senior researcher at the Leibniz Institute for Astrophysics Potsdam (AIP), Germany.

“We see a clear split between ‘impulsive’ particle events, where these energetic electrons speed off the Sun’s surface in bursts via solar flares, and ‘gradual’ ones associated with more extended CMEs, which release a broader swell of particles over longer periods of time,” explained Warmuth.

Confirmation of two electron groups

Scientists long suspected these two types existed. Solar Orbiter made the difference by observing hundreds of events closer to the Sun than ever before. The instruments captured electrons in their early state, offering unmatched clarity.

“We were only able to identify and understand these two groups by observing hundreds of events at different distances from the Sun with multiple instruments – something that only Solar Orbiter can do,” noted Warmuth.

“By going so close to our star, we could measure the particles in a ‘pristine’ early state and thus accurately determine the time and place they started at the Sun.”

Solar flares speed up particles

The theory behind electron acceleration helps explain this split. Solar flares unleash intense magnetic reconnection, which hurls particles outward in short, sharp bursts. These are responsible for impulsive events.

CMEs, in contrast, drive massive shock fronts through the solar atmosphere. As the shock propagates, it accelerates particles over wide regions and longer timescales, explaining the gradual events.

This dual mechanism shows how different physical processes can create electrons with similar energies but distinct signatures in space. It also highlights the Sun as a laboratory of natural particle physics, rivaling human-made accelerators.

Solar particles that seem to lag

Another puzzle involved timing. Sometimes particles seemed to escape hours after a solar flare or CME. Researchers found the lag wasn’t always about late release. Instead, it was partly due to how electrons traveled through turbulent space.

“It turns out that this is at least partly related to how the electrons travel through space – it could be a lag in release, but also a lag in detection,” said co-author and ESA Research Fellow Laura Rodríguez-García.

“The electrons encounter turbulence, get scattered in different directions, and so on, so we don’t spot them immediately. These effects build up as you move further from the Sun.”

Solar wind moves electrons

The space between planets is filled with the solar wind, a stream of charged particles carrying the Sun’s magnetic field. This environment confines and scatters energetic electrons, shaping their journey.

Shock waves, turbulence, and large-scale magnetic structures influence whether electrons reach Earth quickly or after significant delays.

Tracking this behavior is central to the mission. “Thanks to Solar Orbiter, we’re getting to know our star better than ever,” said Daniel Müller, ESA project scientist.

“During its first five years in space, Solar Orbiter has observed a wealth of Solar Energetic Electron events. As a result, we’ve been able to perform detailed analyses and assemble a unique database for the worldwide community to explore.”

Knowing particle origins 

Understanding these processes has practical benefits. The electrons linked to CMEs carry higher risks for satellites and astronauts. Distinguishing them from flare-driven events improves space weather forecasting, giving mission planners valuable warning.

“Knowledge such as this from Solar Orbiter will help protect other spacecraft in the future, by letting us better understand the energetic particles from the Sun that threaten our astronauts and satellites,” said Miller.

“The research is a really great example of the power of collaboration – it was only possible due to the combined expertise and teamwork of European scientists, instrument teams from across ESA Member States, and colleagues from the US.”

Future missions on solar insights

Future missions will build on Solar Orbiter’s success. ESA’s Vigil mission, launching in 2031, will watch the Sun’s side, spotting dangerous eruptions before they face Earth.

Meanwhile, Smile, launching next year, will study how Earth’s magnetic shield interacts with the relentless solar wind.

Together, these missions deepen our grasp of the Sun’s influence, preparing us to live more safely in its ever-changing space environment.

The study is published in the journal Astronomy and Astrophysics.

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