Scientists discover explosive origins of superspeed electrons streaming from the sun

Solar Orbiter took this image of the sun during its close approach in March 2022. At that time, the spacecraft was closer to the star than the solar system's innermost planet Mercury.

Solar Orbiter took this image of the sun during its close approach in March 2022, now, the spacecraft has chased high-speed electrons to the sun to determine that they originate in two types of stellar explosions. (Image credit: ESA)

The joint European Space Agency (ESA) and NASA Solar Orbiter spacecraft has tracked electrons traveling at nearly the speed of light back to the sun, finding they originated in different types of solar outbursts.

Solar Orbiter detected these so-called Solar Energetic Electrons (SEEs) in space after being accelerated to high energies, and researchers were able to pinpoint their source in an attempt to better understand the physics of the sun.

This revealed two distinct types of SEEs with different origins. One group is connected to solar flares exploding from small regions of the sun, while the other population is connected to larger, more powerful outbursts of plasma called 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," team leader and Leibniz Institute for Astrophysics Potsdam (AIP) researcher Alexander Warmuth said in a statement.

Solar researchers already knew that two families of SEEs existed, but the observations of the Solar Orbiter have finally allowed them to distinguish between the origins of these two populations of particles.

"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," Warmuth continued. "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 scientists SEE double trouble

The Solar Orbiter was able to spot SEEs at different distances from the sun, allowing the team to investigate how these particles behave as they journey through the solar system.

One of the aims of this was to discover why there often appears to be a lag in time between the launch of a solar flare or CME erupting from the sun and the release of SEEs into space, as these electrons sometimes take hours to escape the sun.

"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," team member and ESA Research Fellow Laura Rodríguez-Garcíam explained. "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.”

The Solar Orbiter tracks high energy electrons track to the sun find two distinct sources, solar flares and CMEs — The Solar Orbiter tracks high-energy electrons back to the sun to find two distinct sources: solar flares and CMEs. (Image credit: ESA & NASA/Solar Orbiter/STIX & EPD)

The journey that SEEs take through the solar system is influenced by the solar wind, a stream of charged particles that flows from the sun, dragging the star's magnetic field with it. Because SEEs are charged particles, their paths through space are confined and scattered by the solar wind and associated magnetic fields.

The study of SEEs delivered by this research demonstrates how revolutionary Solar Orbiter is in its ability to study the sun and its environment.

"Thanks to Solar Orbiter, we're getting to know our star better than ever," Daniel Müller, ESA Project Scientist for Solar Orbiter, said. "During its first five years in space, Solar Orbiter has observed a wealth of SEE events. As a result, we've been able to perform detailed analyses and assemble a unique database for the worldwide community to explore."

a cube-shaped spacecraft with three stick-like appendages near a fiery orb — An illustration of the Solar Orbiter observing the sun. (Image credit: ESA/AOES)

The team's research could have implications for our understanding of space weather and its impact on spacecraft around Earth. That's because the SEEs launched by CMEs, which are higher energy, can potentially cause much more damage to technology. That means distinguishing between the two types of SEEs could vastly improve space weather predictions.

"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," Müller said. "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."