The European Space Agency's Solar Orbiter spacecraft has provided the clearest evidence yet of how solar flares ignite through a cascading magnetic avalanche. Observations from September 30, 2024, reveal small magnetic disturbances rapidly building into powerful explosions that accelerate particles to near-light speeds. This discovery, detailed in a new study, enhances understanding of these solar events and their potential impacts on Earth.
Solar flares rank among the solar system's most intense explosions, releasing vast energy stored in twisted magnetic fields via magnetic reconnection. On September 30, 2024, during a close approach to the Sun, Solar Orbiter's instruments captured unprecedented details of such an event unfolding over about 40 minutes.
The Extreme Ultraviolet Imager (EUI) recorded high-resolution images of the Sun's corona every two seconds, revealing features just hundreds of kilometers across. Starting at 23:06 Universal Time, a dark, arch-shaped filament of twisted magnetic fields and plasma appeared, linked to a cross-shaped pattern of field lines that brightened gradually. New magnetic strands formed every two seconds or less, twisting like ropes until instability set in.
This led to a chain of reconnections, each more intense than the last, akin to an avalanche. A brightening surge hit at 23:29 UT, followed by the filament detaching and unrolling outward. The main flare peaked around 23:47 UT, with bright flashes along its length.
"We were really very lucky to witness the precursor events of this large flare in such beautiful detail," said Pradeep Chitta, lead author from the Max Planck Institute for Solar System Research in Göttingen, Germany. Instruments like SPICE, STIX, and PHI complemented EUI, tracking energy deposition and particle acceleration to 40-50% the speed of light, or 431-540 million km/h.
Post-flare, plasma blobs rained through the atmosphere, continuing after the peak. X-ray emissions highlighted energy transfer to the corona. "These minutes before the flare are extremely important," Chitta noted, emphasizing the role of smaller events cascading into the larger outburst.
The findings, published January 21, 2026, in Astronomy & Astrophysics, suggest major flares arise from interacting smaller reconnections. ESA's Miho Janvier called it one of Solar Orbiter's most exciting results, questioning if this mechanism applies to all flares and other stars. Co-author David Pontin from the University of Newcastle, Australia, said the observations challenge existing theories, paving the way for refinements.
Solar Orbiter, a joint ESA-NASA mission, underscores the need for advanced monitoring to predict space weather effects like geomagnetic storms disrupting communications.
