Solar Orbiter reveals dual origins of superspeed electrons streaming from Sun

Solar flare seen by EUI and STIX (Image: NASA/ESA)

Space is full of secrets, but the Sun contains some of the most fascinating. It continuously spews forth intense particles, hurtling at high speeds through the Solar System. And now, the European Space Agency's Solar Orbiter mission has revealed new insight into where those particles come from. The latest research shows two distinct sources of energetic electrons emitted by the Sun.

What are solar energetic electrons, and where do they come from?
The Sun accelerates electrons to near light speed. These high-energy electrons, known as Solar Energetic Electrons or SEEs, saturate space. Scientists traced them to two key solar events. One source is intense solar flares, localised explosions on the Sun’s surface. The second source is large coronal mass ejections, or CMEs. CMEs release vast clouds of hot gas into space. Researchers analysed over 300 events between November 2020 and December 2022. They used eight of Solar Orbiter’s ten instruments. The probe’s Energetic Particle Detector measured the particles directly. Meanwhile, other instruments monitored solar activity simultaneously. This dual method linked energetic electrons to their solar origins.

How did Solar Orbiter manage this discovery?
Solar Orbiter flew closer to the Sun than ever before. This proximity let it capture electrons in pristine conditions. Scientists observed particles in situ as the probe passed through them. They combined data on particle streams and solar surface activity. The team utilised extract-compare software to analyze the images in detail. This helped determine 56 tigers grabbed by both flanks and 40 by left flank alone. The survey did not include cubs less than one year of age to prevent bias. The study stands as the most comprehensive SEE analysis to date.

(Image: ESA/NASA)

Why is distinguishing SEE types important for space weather?
Not all energetic electrons are equal in threat. Those tied to CMEs carry more high-energy particles. These can damage satellites and endanger astronauts. Understanding their source helps improve space weather forecasts. Electrons travel through the Solar System under the solar wind. This charged particle stream distorts and delays detection. Turbulence causes electrons to scatter unpredictably. Sometimes they take hours to reach detectors. Solar Orbiter’s measurements reveal these travel effects. Co-author Laura Rodríguez-García explains detection lags are common.

Solar Orbiter's instruments (Image: ESA/NASA)

What’s next for solar observation missions?
ESA’s Vigil mission will launch in 2031. It will observe the Sun’s ‘side’ for the first time. Vigil aims to detect hazardous solar events early. It will improve advance warnings of solar storms. Next year, ESA’s Smile mission will also launch. Smile will study how Earth copes with solar wind. It will analyse particle interactions with Earth’s magnetic field.

Daniel Müller, ESA Project Scientist, praised the collaboration. He said the research offers valuable insights for global scientists. It also strengthens understanding of space weather impacts. Such discoveries will assist in protecting satellites and astronauts. The Solar Orbiter's mission represents a big leap forward.