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Solar flares are powerful explosions on the Sun. They occur when energy stored in tangled magnetic fields is suddenly released through a process described as ‘reconnection’. In a matter of minutes, criss-crossing magnetic field lines of opposite direction break and then reconnect. The newly reconnected field lines can quickly heat up and accelerate million-degree plasma, and even high-energy particles, away from the reconnection site, potentially creating a solar flare.
The most powerful flares may start a chain of reactions that lead to geomagnetic storms on Earth, perhaps triggering radio blackouts, which is why it is so important to monitor and understand them.
But the fine-grained details of how exactly this humungous amount of energy is released so rapidly has remained poorly understood. This unprecedented set of new Solar Orbiter observations – from four of the mission’s instruments working in complement to provide the most complete picture of a solar flare ever made – finally has a compelling answer.
High-resolution imagery from Solar Orbiter’s Extreme Ultraviolet Imager (EUI) zoomed in to features just a few hundred kilometres across in the Sun’s outer atmosphere (its corona), capturing changes every two seconds. Three other instruments – SPICE, STIX and PHI – analysed a range of depths and temperature regimes, from the corona down to the Sun’s visible surface, or photosphere. Importantly, the observations enabled scientists to watch the buildup of events that led to the flare over the course of about 40 minutes.
“We were really very lucky to witness the precursor events of this large flare in such beautiful detail,” says Pradeep Chitta of the Max Planck Institute for Solar System Research, Göttingen, Germany, and lead author of the paper. “Such detailed high-cadence observations of a flare are not possible all the time because of the limited observational windows and because data like these take up so much memory space on the spacecraft’s onboard computer. We really were in the right place at the right time to catch the fine details of this flare.”