Solar Switchbacks Finally Traced to the Sun's Surface

Scientists have traced a mysterious magnetic kink in the solar wind all the way back to the surface of the Sun, solving a long-running puzzle about where solar switchbacks come from. The finding comes from the European Space Agency-led Solar Orbiter spacecraft, which flew directly through one of the giant S-shaped structures and sampled the particles inside, as reported by Phys.org. The work was published in the journal Nature Astronomy.

Solar switchbacks are abrupt, temporary reversals in the direction of the Sun's magnetic field, carried outward by the solar wind — the stream of hot, charged particles that pours off our star. They were first spotted in large numbers near the Sun by NASA's Parker Solar Probe, and they have been a favorite argument in solar physics ever since: two rival theories have competed to explain how they form, and nobody could agree on which one was right.

From S-shape sighting to origin story: how scientists traced solar switchbacks home

The timeline of this discovery stretches back four years. In 2022, Solar Orbiter captured the first-ever image of a switchback in the Sun's outer atmosphere, confirming what theorists had predicted: the kinks really are shaped like the letter S. That image, built from data collected by the spacecraft's EUI and Metis instruments, settled the geometry question.

But geometry is not origin. The breakthrough came from the same 2022 encounter, when Solar Orbiter — positioned roughly halfway between Earth and the Sun — flew straight through an unusually large switchback. That lucky passage gave its Solar Wind Analyser (SWA) instrument a chance to sample the plasma trapped inside the solar switchback.

What the team found was a chemical fingerprint: a specific mix of charged oxygen and carbon particles that, according to the researchers, could only have formed inside hot magnetic field loops anchored at the Sun's surface. That composition points to a formation process called interchange reconnection, where an open magnetic field line collides with a closed loop, the lines snap and reconnect, and plasma that was trapped in the loop escapes into space.

Why solar switchbacks matter for solar storms

"The specific mix of particles detected by Solar Orbiter is the smoking gun for a formation process known as interchange reconnection," said lead author Jesse Coburn of CNRS/LPP in France, according to the study's coverage. The result also carries weight because switchbacks are tied to the deeper question of how the Sun heats its atmosphere and accelerates the solar wind — the same machinery that drives the solar storms that can knock out satellites and power grids.

Here is the twist: the paper does not declare a winner between the two competing theories. Co-author Stephanie Yardley of Northumbria University noted that the team also found signs of the rival explanation — waves and turbulence in the plasma — likely taking over after the solar switchback leaves the Sun. "Overall, it seems that both processes are involved in how switchbacks form and move through space," she said, in the researchers' reconciliation of the debate: interchange reconnection builds the structure at the surface, and waves and turbulence govern how it travels.

That matters for space weather forecasting. Daniel Müller, ESA's project scientist for Solar Orbiter, said the results have key implications for keeping the planet safe from extreme space weather events, "to protect our space-based infrastructure and technology." In other words, knowing where solar switchbacks are born is a step toward predicting when the Sun's moods will reach Earth. Each solar switchback is a small chapter in the larger story of how a magnetic disturbance at the Sun becomes a forecast problem for satellites.

The team reached the Sun-side conclusion by combining the in-place particle measurements with images of the solar disk and a new model linking the plasma to data from NASA's Solar Dynamics Observatory — effectively reading a return address written into the particles themselves. As described in further coverage, different regions of the solar atmosphere imprint different chemical signatures on the plasma they release, which is what made the fingerprint possible.

What comes next: the method opens a way to read the history of solar plasma long after it has left the Sun. Solar Orbiter keeps orbiting closer in, and Parker Solar Probe is still sampling the young solar wind — so the next few years of solar switchbacks research may finally turn a decades-old argument into settled physics.

Related: continue with more science coverage, and see how Webb chased a different cosmic mystery in Most Distant Fast Radio Burst Traced to a Tiny Galaxy.