The Solar Orbiter mission from the European Space Agency has made its latest discovery, tracing two distinct types of solar energetic electrons to their origins in separate events, and providing new tools to aid scientists in predicting dangerous space weather events.
Published in Astronomy & Astrophysics, the new work explores how the Sun, acting as a particle accelerator, accelerates electrons to nearly the speed of light before shooting them out into space as solar energetic electrons (SEEs). The work began with locating these particles, tracing their origins, and then connecting them to specific solar events, including intense solar flares and coronal mass ejections (CMEs).
“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,” says lead author Alexander Warmuth of the Leibniz Institute for Astrophysics Potsdam (AIP), Germany.
Understanding Solar Energetic Electrons
Previous work had discerned that SEE events came in two varieties, solar flares and CMEs, which the new Solar Orbiter data provided a significant number of new examples for. This new evidence enabled the researchers to understand how SEEs form and emerge from the solar surface.
“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,” adds Alexander. “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.”
A major component of the data was that SEE events were detected at varying distances from the Sun, providing evidence for how the electrons behave on their travels across the solar system.
Solar Orbiter Answers Questions
One of the most interesting questions the new work helps answer is the perplexing lag between solar events and the escape of energetic electrons, which can sometimes last hours.
“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,” says 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.”
Filling the void between the Sun and its planets is the solar wind, a stream of particles emanating from the Sun and carrying with it the Sun’s magnetic field. Due to its magnetism, the wind confines, scatters, and disturbs energetic electrons that cross its path. The new research, which tracks the paths of those electrons, provides new data on these influences.
“Thanks to Solar Orbiter, we’re getting to know our star better than ever,” says Daniel Müller, ESA Project Scientist for Solar Orbiter. “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.”
Space Weather Safety
The most pressing concern for life on Earth is what this all means in terms of space weather. SEE events originating from coronal mass ejections can have serious adverse effects on our technological infrastructure, both on the ground and in near-Earth orbit. By enabling space weather forecasters to distinguish specifically those SEEs originating from coronal mass ejections, the research is a boon to our understanding of space weather.
“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,” adds Daniel. “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.”
Understanding the effect of solar emissions on the Earth will be further advanced with the launch of another European Space Agency mission next year called Smile. The Smile mission will focus on the solar wind and its interaction with Earth’s magnetic field.
The paper, “CoSEE-Cat: a Comprehensive Solar Energetic Electron Event Catalogue Obtained from Combined In-situ and Remote-sensing Observations from Solar Orbiter,” appeared in Astronomy and Astrophysics on September 1, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.