The European Space Agency-led Solar Orbiter mission has made significant strides in the study of Solar Energetic Electrons (SEEs), categorizing them into two distinct groups and tracing their origins back to different solar outbursts. This groundbreaking research highlights the Sun as the most potent particle accelerator in our Solar System, capable of propelling electrons to nearly the speed of light and flooding the Solar System with energetic particles.
Using the Solar Orbiter, researchers have successfully identified the sources of these energetic electrons. The study reveals two primary types of SEEs, each with unique characteristics: one type is linked to intense solar flares, which are explosive eruptions from smaller regions of the Sun's surface, while the other is associated with larger outflows of hot gas known as coronal mass ejections (CMEs). According to lead author Alexander Warmuth from the Leibniz Institute for Astrophysics Potsdam (AIP), “We see a clear split between ‘impulsive’ particle events, where energetic electrons burst off the Sun’s surface during solar flares, and ‘gradual’ events linked to extended CMEs, releasing a broader spectrum of particles over time.”
Previously, scientists recognized the existence of two types of SEE events, but the Solar Orbiter has allowed for a much closer observation of these phenomena. By measuring a significant number of events and utilizing its advanced instruments, Solar Orbiter has provided insights into how these energetic electrons form and escape from the Sun's surface. “We were only able to identify and understand these two groups by observing hundreds of events at varying distances from the Sun using multiple instruments – something that only Solar Orbiter can achieve,” Alexander added. The study utilized eight of the ten instruments aboard the Solar Orbiter to observe over 300 events between November 2020 and December 2022.
This research represents the most thorough analysis of SEE events to date, establishing a catalogue that will expand as the Solar Orbiter continues its mission. Co-author Frederic Schuller, also from AIP, emphasized the significance of their findings: “It’s the first time we’ve clearly seen this connection between energetic electrons in space and their originating events at the Sun.” The Solar Orbiter not only flew through the electron streams but also gathered data on the conditions in space between the Sun and the spacecraft, enriching our understanding of these energetic particles.
The study revealed that researchers detected SEE events at various distances from the Sun, allowing them to analyze how electrons behave as they traverse the Solar System. Often, there is a noticeable delay between the occurrence of a solar flare or CME and the subsequent release of energetic electrons into space. “This delay could stem from how electrons travel, influenced by turbulence and scattering in space,” co-author and ESA Research Fellow Laura Rodríguez-García explained. The charged particles emitted by the Sun create a wind that fills space and affects how energetic electrons travel, causing them to scatter and get delayed.
These findings are crucial for enhancing our understanding of space weather, where accurate forecasting is vital for protecting spacecraft and astronauts. Among the two types of SEE events, those connected to CMEs pose a more significant threat due to their higher energy levels. As Daniel Müller, ESA Project Scientist for Solar Orbiter, pointed out, “Knowledge from Solar Orbiter will help protect other spacecraft in the future by improving our understanding of the energetic particles from the Sun that pose risks to our technology and astronauts.”
Looking ahead, ESA's upcoming Vigil mission aims to revolutionize solar observation by monitoring the 'side' of the Sun, providing continuous insights into solar activity. Scheduled for launch in 2031, Vigil will detect potentially hazardous solar events before they become visible from Earth, offering crucial information about their speed and direction. Additionally, the Smile mission, set to launch next year, will further investigate how Earth reacts to solar storms and the interaction of solar particles with our planet's magnetic field.
The Solar Orbiter is a remarkable example of international collaboration between ESA and NASA, operated by ESA. The findings from this mission not only enhance our understanding of the Sun but also contribute to the global efforts in space weather monitoring. For more information on the Solar Orbiter mission and its instruments, visit the official ESA website.
For further reading, you can access the study titled ‘CoSEE-Cat: a Comprehensive Solar Energetic Electron event Catalogue obtained from combined in-situ and remote-sensing observations from Solar Orbiter’ published in Astronomy & Astrophysics. The results are compiled in an online event catalogue, the Comprehensive Solar Energetic Electron event Catalogue (CoSEE-Cat), available at here.
