Magnetic avalanche in action
Solar Orbiter’s most detailed view yet of a large solar flare, observed during its 30 September 2024 close approach to the Sun.
The imagery was published in 2025, but now scientists have focused in on the details to uncover an exciting and surprising result: individual solar flares are triggered by initially weak disturbances that quickly become more violent – much like an avalanche on a snowy mountain. This rapidly evolving process creates a ‘sky’ of raining plasma blobs that continue to fall even after the flare subsides.
For the first time, this process is revealed in the video shown here, along with the supplementary videos featured in the full story.
When Solar Orbiter’s Extreme Ultraviolet Imager (EUI) first started observing the region at about 23:06 Universal Time (UT), a dark arch-like ‘filament’ of twisted magnetic fields and plasma was already present, connected to a cross-shaped structure of progressively brightening magnetic field lines.
Zooming in to this feature shows that new magnetic field strands are appearing in every image frame – equivalent to every two seconds or less. Each strand is magnetically contained, and they become twisted, like ropes. Then, just like in a typical avalanche, the region becomes unstable. The twisted strands begin to break and reconnect, rapidly triggering a cascade of further destabilisations in the area. This creates progressively stronger reconnection events and outflows of energy, seen as increasing brightness in the imagery.
A sudden brightening begins at 23:29 UT, followed by the dark filament disconnecting from one side, launching into space and at the same time violently unrolling at high speed. The unwinding closest to the footprint is recorded at 250 km/s, increasing to 400 km/s at the site of disconnection. Bright sparks of reconnection are seen all along the filament in stunning high resolution as the flare erupts at 23:47 UT.
At the same time, ribbon-like features are seen moving extremely quickly down through the Sun’s atmosphere. These streams of ‘raining plasma blobs’ are signatures of energy deposition from the reconnection events, which get stronger and stronger as the flare progresses. Even after the flare subsides, the rain continues for some time.
While EUI captured this high-resolution imagery, Solar Orbiter’s SPICE and STIX instruments monitored the temperatures and particle emissions at different layers in the Sun’s atmosphere. They revealed the slow rise of ultraviolet to x-ray emission prior to the flare, followed by a dramatic increase in x-ray emission during the main phase of the flare – signifying that particles were accelerated to 40-50% the speed of light equivalent to about 431–540 million km/h. This was recorded close to the base of the filament connection point as it unfurled into space.
After the main phase of the flare, the original cross-shape of magnetic field lines relaxes and the instruments see the plasma cool down to ‘normal’ levels. Bundles of looped magnetic field lines and suspended plasma – ‘arcades’ – hang over the flare site for some time.
Solar Orbiter is a space mission of international collaboration between ESA and NASA. The EUI instrument is led by the Royal Observatory of Belgium (ROB).
