Solar Orbiter Traces Origins of Superfast Electrons from the Sun

The European Space Agency (ESA) and NASA's Solar Orbiter mission has made significant strides in understanding the origins of Solar Energetic Electrons (SEEs), which are electrons accelerated to nearly the speed of light and ejected from the Sun. Between November 2020 and December 2022, Solar Orbiter observed over 300 bursts of SEEs, identifying two distinct sources: solar flares and coronal mass ejections (CMEs). This research, published in the journal *Astronomy & Astrophysics*, marks the first clear connection between energetic electrons detected in space and their origins on the Sun.

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Researchers have categorized SEEs into two groups based on their origins. The first group is associated with solar flares, which release quick bursts of energetic electrons from smaller regions of the Sun. The second group is linked to CMEs, larger explosions that release a broader swell of particles over extended periods. Alexander Warmuth, a researcher from the Leibniz Institute for Astrophysics Potsdam, stated, “We see a clear split between ‘impulsive’ particle events... and ‘gradual’ ones associated with more extended CMEs.”

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A key aspect of the research was understanding the lag time between solar events and the release of SEEs into space. Laura Rodríguez-García, an ESA Research Fellow, explained that this lag could be attributed to the electrons encountering turbulence and being scattered in different directions as they travel through space. This scattering complicates the detection of SEEs, which can take hours to escape the Sun after a flare or CME occurs.

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The findings from Solar Orbiter have crucial implications for space weather forecasting. The SEEs associated with CMEs are particularly significant due to their higher energy levels, which pose a greater risk to spacecraft and technology on Earth. Daniel Müller, ESA Project Scientist for Solar Orbiter, emphasized that understanding these energetic particles will enhance the protection of astronauts and satellites. “Knowledge such as this from Solar Orbiter will help protect other spacecraft in the future,” Müller stated.

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Looking ahead, ESA plans to launch the SMILE mission in 2026, which will study the solar wind and its interaction with Earth's magnetosphere. Additionally, the Vigil mission, set for launch in 2031, aims to observe the Sun's "side" to detect potentially hazardous solar events before they become visible from Earth. These future missions will build on the foundational knowledge gained from Solar Orbiter, further enhancing our understanding of solar activity and its effects on space weather.

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• “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,” — Alexander Warmuth, Researcher, Leibniz Institute for Astrophysics Potsdam

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• “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.” — Daniel Müller, ESA Project Scientist for Solar Orbiter

Solar Orbiter: Revealing what happens on the Sun’s surface

• “The electrons encounter turbulence, get scattered in different directions, and so on, so we don’t spot them immediately.” — Laura Rodríguez-García, ESA Research Fellow

Solar Orbiter: Revealing what happens on the Sun’s surface

While the research has clarified the origins of SEEs, questions remain regarding the precise mechanisms of electron scattering and detection delays. Further studies are needed to fully understand these processes and their implications for space weather forecasting.

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