Much like a snow avalanche that starts with a small shift before cascading downhill, new observations show that solar flares begin with subtle magnetic disturbances that rapidly intensify. Scientists using the European Space Agency (ESA) led Solar Orbiter spacecraft discovered that these early changes can quickly grow into violent eruptions, producing a dramatic cascade of glowing plasma blobs that fall through the Sun’s atmosphere long after the main flare has peaked.
This insight comes from one of the most detailed views ever captured of a large solar flare. The event was recorded during Solar Orbiter’s close pass by the Sun on 30 September 2024 and is described in a study published today (January 21) in Astronomy & Astrophysics.
What Triggers a Solar Flare
solar flares are among the most powerful explosions in the solar system. They occur when enormous amounts of energy stored in twisted magnetic fields are suddenly released through a process known as magnetic reconnection. During reconnection, magnetic field lines pointing in opposite directions break apart and reconnect in a new configuration. This rapid rearrangement can heat plasma to millions of degrees and hurl energized particles away from the site, creating a solar flare.
The strongest flares can set off a chain reaction that reaches Earth, triggering geomagnetic storms and sometiems disrupting radio communications. Because of these potential impacts, scientists are eager to understand exactly how flares begin and evolve.
For years, the precise mechanism behind the Sun’s ability to release such vast energy in minutes remained unclear. Now, a rare combination of observations from four Solar Orbiter instruments working together has provided the most complete picture yet of how a flare unfolds from its earliest moments.
A Rare Look at the Birth of a Solar Flare
Solar Orbiter’s Extreme Ultraviolet Imager (EUI) captured remarkably detailed images of the Sun’s outer atmosphere, known as the corona, resolving features only a few hundred kilometers across and recording changes every two seconds. At the same time, three additional instruments, SPICE, STIX and PHI, studied different layers of the sun, from the hot corona down to the visible surface, or photosphere.
Together, these observations allowed scientists to track the buildup to the flare over roughly 40 minutes, an prospect that rarely occurs due to limited observing windows and onboard data constraints.
“We were really very lucky to witness the precursor events of this large flare in such lovely detail,” says pradeep Chitta of the Max Planck Institute for Solar System Research, Göttingen, Germany, and led author of the paper. ”Such detailed high-cadence observations of a flare are not possible all the time as 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.”
Magnetic Avalanche in Action
When EUI began observing the region at 23:06 Universal time (UT), about 40 minutes before the flare reached its peak, it revealed a dark, arch shaped filament made of twisted magnetic fields and plasma. This structure was connected to a cross shaped pattern of magnetic field lines that gradually grew brighter. (See video link below article.)
Close up views showed that new magnetic strands appeared in nearly every image frame, roughly every two seconds or less. Each strand remained confined by magnetic forces and gradually twisted, resembling tightly wound ropes.
As more strands formed and twisted, the region became unstable. Like an avalanche gaining momentum, the magnetic structures began breaking and reconnecting in rapid succession. This triggered a spreading chain of disruptions, each one stronger than the last, visible as sudden bursts of brightness.
At 23:29 UT, a particularly intense brightening occured. Soon after, the dark filament detached on one side and shot outward, unrolling violently as it moved. Bright flashes of reconnection appeared along its length in extraordinary detail as the main flare erupted around 23:4
