The sun is more than the bright disk we see rising every morning. It is a colossal nuclear furnace, a stormy giant of plasma and magnetism, and the single most powerful particle accelerator in the solar system. From its fiery surface and turbulent atmosphere, it hurls streams of energy and particles across space—sometimes gently, sometimes violently. These eruptions are not confined to the star itself; they ripple across the solar system, reaching the planets, shaping space weather, and even threatening the technology and astronauts who rely on a fragile layer of protection around Earth.
Now, thanks to the European Space Agency’s Solar Orbiter mission, scientists have peeled back a new layer of mystery. They’ve traced the origins of one particularly elusive phenomenon: the bursts of high-speed electrons that escape from the sun, known as Solar Energetic Electrons (SEEs). And what they discovered reveals a story in two parts—a tale of sudden bursts and slower, swelling storms.
The Race of Solar Electrons
Electrons are tiny, but when the sun accelerates them, they become cosmic sprinters, reaching speeds close to that of light itself. Imagine the sun as a vast engine, whipping these particles into motion and flinging them across millions of kilometers. Once released, the electrons stream through the solar system, sometimes racing ahead of other solar material, sometimes hidden in the turbulence of solar storms.
For decades, scientists knew that SEEs arrived at Earth and beyond in two distinct ways, but their precise origins remained fuzzy. Were they all born in the same kind of solar event? Or did the sun have more than one mechanism for launching them into space?
Solar Orbiter—designed to fly closer to the sun than any other European spacecraft before it—finally provided the missing clarity.
Two Families of Solar Outbursts
The results, published in Astronomy & Astrophysics, confirm what many suspected but could not prove: the sun produces two distinct kinds of SEE events, each tied to a different kind of solar eruption.
The first group is linked to solar flares. These are intense explosions of energy that erupt from smaller patches on the sun’s surface, like sparks leaping from a bonfire. The electrons accelerated here are impulsive—quick bursts that shoot out suddenly, filling space with streams of fast, energetic particles.
The second group is tied to coronal mass ejections (CMEs). These are far larger events—enormous eruptions of hot, magnetized gas blasted outward from the sun’s outer atmosphere. Instead of a sharp burst, they unleash a gradual flood of electrons, spreading across space for hours or even days. CMEs, while slower to ramp up, carry more high-energy particles and have a far greater potential to disrupt satellites, power grids, and astronaut safety.
As Alexander Warmuth of the Leibniz Institute for Astrophysics in Potsdam, lead author of the study, put it: “We see a clear split between ‘impulsive’ particle events, where energetic electrons speed off in bursts via solar flares, and ‘gradual’ ones linked to CMEs, which release a broader swell of particles over time.”
Why the Delay? The Puzzle of Timing
One of the lingering mysteries about solar electrons has been the apparent delay between seeing an eruption on the sun and detecting the electrons in space. Sometimes the particles seem to take hours to escape—odd, given their near-light speeds.
Solar Orbiter helped untangle this puzzle. The electrons don’t always travel in straight lines. Instead, as Laura Rodríguez-García, ESA Research Fellow and co-author of the study, explained, they are buffeted by turbulence in the solar wind. The solar system is filled with this invisible stream of charged particles and magnetic fields, which scatter, redirect, and delay the electrons. What looks like a “late release” from the sun is often a complex journey, as the electrons zigzag through space before reaching our detectors.
This discovery was only possible because Solar Orbiter measured the electrons much closer to their birthplace, capturing them in a more “pristine” state before their paths became scrambled.
Watching the Sun Up Close
Solar Orbiter is uniquely equipped for this detective work. Orbiting closer than Mercury at times, it carries a suite of instruments that can simultaneously watch the sun’s surface and measure the particles streaming outward. By observing hundreds of SEE events at different distances, the mission was able to map the timing and origins of each burst with unprecedented precision.
This ability to trace the chain of cause and effect—from flare or CME on the sun to the detection of electrons in space—is central to understanding solar activity. It fulfills one of Solar Orbiter’s primary goals: connecting the dots between what we see on the solar surface and what we measure in the solar wind.
As Daniel Müller, ESA’s Project Scientist for Solar Orbiter, noted: “Thanks to Solar Orbiter, we’re getting to know our star better than ever. The mission has already created a unique database for scientists worldwide to explore.”
Why It Matters for Earth
This discovery is not only a triumph of curiosity—it has real-world consequences. Understanding the two kinds of SEE events is crucial for improving space weather forecasting. Just as meteorologists track storms on Earth to warn of floods or hurricanes, space scientists track solar storms to protect satellites, spacecraft, and astronauts.
Of the two types of SEE events, those tied to CMEs are far more dangerous. Their broad, sustained floods of high-energy particles can disable spacecraft electronics, interfere with communications, and endanger astronauts outside Earth’s protective magnetic field. By distinguishing between impulsive flare-driven events and gradual CME-driven ones, scientists can better predict which solar outbursts pose real risks.
“Knowledge such as this will help protect other spacecraft in the future,” Müller added, “by letting us better understand the energetic particles from the sun that threaten our astronauts and satellites.”
The Road Ahead: Vigil and Smile
Solar Orbiter is not working alone. Its success sets the stage for new missions that will extend our solar forecasting abilities even further.
ESA’s Vigil mission, launching in 2031, will provide humanity with a brand-new perspective: monitoring the sun from the side. Instead of watching only what faces Earth, Vigil will give advance warning of eruptions rotating toward our planet, allowing scientists to track their speed, direction, and potential impact before they strike.
Meanwhile, ESA’s Smile mission, launching next year, will study Earth’s magnetic shield—the invisible bubble that protects us from the worst of the solar storm onslaught. By watching how the planet’s magnetosphere flexes and bends under the impact of solar wind, Smile will help us understand how Earth endures both the constant solar breeze and sudden particle storms.
Together with Solar Orbiter, these missions are weaving a fuller picture of the dynamic relationship between our star and our world.
A Deeper Connection to Our Star
The Solar Orbiter findings remind us of something profound: the sun is not a static backdrop to our lives, but a restless, dynamic force. Its storms shape the very space through which we travel, affecting satellites, spacecraft, and even daily technologies we rely on.
By splitting the mystery of Solar Energetic Electrons into two clear families, Solar Orbiter has not just solved a long-standing puzzle—it has deepened our connection to the star that gives us life. Each new discovery reminds us that to live safely in the solar system, we must understand the rhythms and tempests of our parent star.
And perhaps, just as our ancestors once looked up at the sun and wondered about its power, we are now entering a new era: one where we don’t just wonder, but truly begin to understand.
More information: CoSEE-Cat: a Comprehensive Solar Energetic Electron event Catalogue obtained from combined in-situ and remote-sensing observations from Solar Orbiter, Astronomy and Astrophysics (2025). DOI: 10.1051/0004-6361/202554830
