Solar Orbiter Captures ‘Magnetic Avalanche’ Building a Major Solar Flare

From nearly 70 million miles away, a European spacecraft has watched the Sun build up to a major explosion not as a single, sudden blast, but as a chain reaction of tiny magnetic failures rippling across its surface.

A flare powered by a cascade, not a single snap

In a study published this month in Astronomy & Astrophysics, scientists report that ESA’s Solar Orbiter mission captured one of the most detailed views yet of a large solar flare—and found that it was powered by what they call a “magnetic avalanche.” Rather than releasing energy in one smooth, coherent event, the flare grew from a cascade of many small magnetic reconnection episodes that spread through the Sun’s atmosphere over nearly an hour.

“We were really very lucky to witness the precursor events of this large flare in such beautiful detail,” said lead author Pradeep Chitta, a solar physicist at the Max Planck Institute for Solar System Research in Göttingen, Germany. “We were in the right place at the right time to catch the fine details of this flare.”

The observations provide some of the clearest evidence yet that major flares can behave like avalanches in a sandpile—an idea theorists have proposed for decades but that has been difficult to demonstrate in a single, well-resolved event. The result comes as the Sun enters a more active phase than many forecasters expected, with recent storms disrupting satellites, navigation systems and radio communications on Earth.

What Solar Orbiter saw on Sept. 30, 2024

Solar Orbiter recorded the flare on Sept. 30, 2024, during its ninth close pass around the Sun. The spacecraft was about 0.29 astronomical units from our star—inside Mercury’s orbit—when its cameras tracked a magnetically tangled active region on the visible disk.

By 23:06 Coordinated Universal Time, the mission’s Extreme Ultraviolet Imager was already seeing a dark, arching filament of dense solar material suspended above the surface by twisted magnetic fields. The filament was anchored to a bright, cross-shaped structure below, where the magnetic field was particularly stressed.

Over the next 40 minutes, new strands of glowing plasma appeared around the filament roughly every two seconds. Those strands traced coronal magnetic field lines twisting and kinking like ropes under tension. At dozens of locations, tiny flashes appeared and faded—signatures of small reconnection events, where magnetic field lines snap and rejoin, releasing bursts of energy.

“We were surprised by how the large flare is driven by a series of smaller reconnection events that spread rapidly in space and time,” Chitta said.

Around 23:29 UTC, one side of the filament suddenly lost its magnetic foothold. The structure whipped upward and outward, marking the start of a major eruption. The flare formally peaked at 23:47 UTC, reflected in its official designation: SOL2024‑09‑30T23:47.

Instruments confirm particle acceleration and plasma flows

As the flare unfolded, Solar Orbiter’s instrument suite filled in the broader physics:

• The STIX X-ray telescope detected a sharp rise in high-energy emission, indicating particles accelerated to 40%–50% of the speed of light.
• The SPICE spectrometer observed fast-moving streams of hot plasma.
• The PHI instrument tracked changes in the magnetic field at the solar surface below.

After the peak, images showed bright, ribbon-like curtains of material raining back down through the corona in narrow lanes. These “plasma blobs” traced where energy from the reconnection cascade was deposited into lower atmospheric layers, heating them and driving flows.

Why the “avalanche” idea matters

Scientists have long known that solar flares draw their power from magnetic reconnection, in which magnetic field lines in a conductive plasma break and realign, rapidly converting stored magnetic energy into heat, light and fast particles. But the geometry and timing of reconnection during large flares has been hard to pin down, limited by earlier instruments’ resolution and imaging cadence.

The new data suggest that, in this case, the corona did not undergo a single coherent reconfiguration. Instead, small patches of reconnection lit up first, subtly altering nearby fields and pushing neighboring regions toward instability. The flare grew as these instabilities cascaded across the active region.

“Solar Orbiter’s observations unveil the central engine of a flare and emphasise the crucial role of an avalanche-like magnetic energy release mechanism at work,” said Miho Janvier, co-project scientist for Solar Orbiter at the European Space Agency.

The avalanche concept draws on self-organized criticality, a framework proposed in the early 1990s. In it, the corona behaves like a sandpile: slow, steady driving—here, motions at the Sun’s surface—loads energy into magnetic fields until the system reaches a critical state where a small disturbance can trigger events of many sizes.

Self-organized criticality has helped explain the statistics of flares, including why small and large events follow similar power-law size distributions. But until now, support often came from long-term surveys and simplified simulations rather than a time-resolved view of a single large flare.

Researchers say the Sept. 30 flare ties that decades-old theoretical picture to direct imaging and spectroscopy of a real event.

Space-weather stakes during Solar Cycle 25

The finding arrives during Solar Cycle 25, which began in late 2019 and has already produced some of the strongest activity in more than two decades. In May 2024, a series of eruptions triggered a G5 geomagnetic storm—NOAA’s highest category—lighting up skies as far south as the Caribbean and causing power-grid fluctuations and GPS errors. In January, an X-class flare on Jan. 18 prompted warnings to satellite operators and high-latitude flights after the most intense solar radiation storm in 23 years.

These episodes have underscored how dependent modern economies are on technologies vulnerable to space weather. Strong solar storms can induce currents that damage transformers, degrade or disable satellites, disrupt high-frequency radio used by aircraft and ships, and increase radiation exposure for astronauts and passengers on polar flights. Some economic studies suggest that, in extreme scenarios, U.S. power-grid disruptions alone could cost billions of dollars a day.

Understanding how large flares ignite is therefore more than academic. The Solar Orbiter team notes that the Sept. 30 event had a clear pre-flare phase of roughly 40 minutes, during which the rate and intensity of small reconnection events increased before the main outburst. If similar precursor patterns appear in other events, they could provide forecasters with short-term warning signs.

Chitta said the team “didn’t expect that the avalanche process could lead to such high energy particles,” highlighting the link between small-scale magnetic dynamics and radiation hazards to spacecraft and astronauts.

What remains unknown

Scientists caution the study is based on a single flare observed under near-ideal conditions. High-speed, high-resolution imaging generates enormous amounts of data, and missions cannot watch the entire Sun at two-second cadence continuously. It remains unclear whether all large flares follow the same avalanche pattern, or whether other mechanisms dominate under different conditions.

Researchers are also still investigating how internal avalanche behavior relates to coronal mass ejections—vast plasma clouds that can drive the most damaging geomagnetic storms at Earth—and whether certain avalanche signatures correlate with eruptions that are more “geoeffective,” meaning they couple strongly to Earth’s magnetic field.

Janvier said a key question is whether similar avalanche-like processes occur “in all flares, and on other flaring stars.” Answering it will require more events, more coordinated campaigns with other solar observatories and continued operation of Solar Orbiter as it moves into higher-inclination orbits to view the Sun’s polar regions.

Solar Orbiter’s nominal mission runs through the end of 2026, with a possible extension into the next decade. As the Sun moves through the peak of its current cycle, the spacecraft is expected to capture many more flares and eruptions from vantage points no other mission can match.

For now, the Sept. 30 flare offers a rare look under the hood of one of nature’s most powerful engines—and a reminder that the Sun’s most dramatic outbursts can grow from countless small failures, cascading until they light up half the solar system.