Scientists discover explosive origins of superspeed electrons streaming from the sun

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 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.”

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.”

Scientists will get an even better picture of the impact of solar outbursts when the ESA launches its Smile mission in 2026. Smile will measure the solar wind and how it interacts with Earth’s magnetic bubble, the magnetosphere.

Further into the future, in 2031, the ESA mission solar observing spacecraft Vigil will launch. Vigil will aim to examine the “side” of the sun with the aim of spotting potentially damaging solar events at the limb of the sun before they turn toward Earth. This should improve space weather predictions substantially by allowing scientists to determine the power, direction, and chance of impact upon Earth of solar outbursts.

The team’s research was published on Monday (Sept. 1) in the journal Astronomy & Astrophysics.