Often described as the most powerful particle accelerator in the solar system, the sun can whip electrons to near light speed, releasing torrents of so-called solar energetic electrons (SEE). These electrons can disrupt satellites, communications and power systems on Earth, making it critical for scientists to understand how and when they are produced.
Using observations gathered closer to the sun than ever before, researchers have now traced these electrons back to their source. The study reveals two different pathways: fast, “impulsive” events linked to solar flares explosions on the sun’s surface and slower, “gradual” events associated with vast coronal mass ejections (CME), when hot plasma erupts from the sun’s atmosphere.
“We see a clear divide between the two types,” said lead author Alexander Warmuth of the Leibniz Institute for Astrophysics Potsdam (AIP) in Germany. “Impulsive events are triggered by solar flares, sending electrons racing outwards in short bursts, while gradual events are tied to CMEs, which release broader streams of particles over much longer periods.”
While scientists have long suspected this dual origin, Solar Orbiter’s instruments provided the clearest evidence yet. Between late 2020 and the end of 2022, the spacecraft used eight of its 10 instruments to observe more than 300 events.
“We could only distinguish these two groups by recording hundreds of examples at varying distances from the sun,” Warmuth said. “By flying so close, Solar Orbiter was able to detect the particles in a near-pristine state and trace them back precisely to when and where they were launched.”
Co-author Frederic Schuller, also from AIP, explained that the probe not only measured the electrons directly using its Energetic Particle Detector but also simultaneously watched the sun’s surface and the conditions in space between the star and the spacecraft. “It’s the first time we’ve clearly seen the direct connection between electrons in space and the events that created them on the sun,” he said.
The findings carry significant implications for space weather forecasting. Among the two types of SEE, those linked to CMEs pose the greater risk to satellites and astronauts, as they carry higher-energy particles and can cause far more damage. Distinguishing between them could therefore improve early warning systems.
“Knowledge like this is vital for protecting future spacecraft and astronauts,” said European Space Agency (ESA) project scientist Daniel Müller. “This research is a great example of international collaboration, drawing on expertise across Europe and the United States.”
ESA’s Solar Orbiter is just the beginning of a broader push to better understand the sun. The agency’s Vigil mission, due for launch in 2031, will provide the first continuous view of the sun’s “side”, allowing earlier detection of hazardous solar eruptions before they rotate into Earth’s line of sight.
Next year, ESA will also launch the Smile mission, designed to study how Earth’s magnetic field responds to solar storms and the constant barrage of particles from our star. Together, these missions will help scientists not only forecast dangerous events, but also better understand how our planet weathers the sun’s relentless activity.