ESA’s Solar Orbiter traced the solar wind’s mysterious magnetic switchbacks to the Sun’s surface

A single burst of solar wind that Solar Orbiter happened to fly through has given scientists their clearest link yet between the Sun’s magnetic kinks and the surface they came from. The kinks, called switchbacks, are S-shaped folds in the magnetic field carried outward by the solar wind, and the particles inside this one carried a chemical fingerprint of charged oxygen and carbon that points back to hot magnetic loops on the Sun.

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The measurements were taken while the European Space Agency spacecraft sat roughly midway between Earth and the Sun. Switchbacks have puzzled solar physicists for years, partly because they are common near the Sun yet vanish into the background farther out, making their birthplace hard to pin down.

Charged oxygen and carbon as a fingerprint

The work, published Oct. 8 in the journal Nature Astronomy titled “On the Coronal Origin of Magnetic Switchbacks in the Solar Wind”, is led by Jesse Coburn of CNRS/LPP in France. As ESA reported, the Solar Wind Analyser on Solar Orbiter sampled the plasma inside the switchback, and the mix included charged oxygen and carbon particles. According to the paper, the data came from March 2, 2022, when the spacecraft was about 0.55 astronomical units from the Sun, where one astronomical unit is the distance between Earth and the Sun.

Charge states act like a thermometer that stays attached to the plasma. Oxygen and carbon ions end up with particular charges only when they form in very hot, closed regions of the solar atmosphere, and those charges do not change much afterward. The team concluded that the switchback plasma had been released from such hot loops, and the paper also reports that helium was depleted relative to protons, another sign of that source.

Coburn described the encounter in plain terms, saying that Solar Orbiter had flown through a very large switchback and sampled rarely observed particles that carry signatures of their origin.

Switchbacks are not new to the field. NASA’s Parker Solar Probe has encountered them frequently in recent years close to the Sun, while older missions Helios 1 and 2 and Ulysses recorded them farther out, but only as in situ measurements taken as the spacecraft passed through. In 2022, researchers at the Max Planck Institute for Solar System Research led by Daniele Telloni used Solar Orbiter’s Metis coronagraph and Extreme Ultraviolet Imager to catch one on camera on March 25, 2022, a structure several hundred thousand kilometers across moving outward at no less than 290,000 kilometers per hour, as the Max Planck Society reported. Imaging showed where such a structure begins; the new composition data show what it is made of. More on the spacecraft itself is gathered on ESA’s Solar Orbiter pages.

Interchange reconnection against waves and turbulence

To locate the source, the researchers linked the spacecraft measurements to a model of the solar atmosphere that used data from NASA’s Solar Dynamics Observatory. The model traced the plasma either to the boundary of a coronal hole or to small loops inside one, with loop lengths estimated at roughly 8 to 12 megameters, according to the paper. That points to a process known as interchange reconnection, in which closed magnetic loops meet open field lines and fling their trapped plasma into space.

Interchange reconnection is one of two leading ideas. The rival explanation says switchbacks arise from waves and turbulence in the solar wind itself. Stephanie Yardley of Northumbria University, a co-author, said that once a switchback has left the Sun, waves and turbulence take over and govern how it moves. The result therefore does not knock out the wave idea; it suggests each process operates at a different stage of a switchback’s life, with reconnection creating the structure and turbulence shaping its journey.

The authors also found proton velocity and magnetic fluctuations that match an outward-traveling Alfven wave, which fits that second stage. Their wider claim is that switchbacks preserve measurable signatures of coronal heating and solar wind acceleration, so the structures may work as a tracer linking the solar atmosphere to material found far from the Sun.

Limits of one switchback and the value for space weather

Caution is built into the work. The study rests on a single case, and the paper notes that the magnetic field modeling carries uncertainty, in particular from the height of the source surface, which the authors varied between 1.5 and 3 solar radii. They call for larger statistical studies to test whether the same origin holds for other switchbacks.

Daniel Müller, ESA’s project scientist for Solar Orbiter, said the discovery would not have been possible without the spacecraft, which he said connects the Sun to its wider environment. ESA frames the stakes in practical terms: the better the origin of the solar wind is understood, the better solar storms can be prepared for. Earlier observations from the same spacecraft, including the 2022 image-based tracing by Max Planck researchers, had already linked a switchback to the lower corona; the new result adds the chemical evidence.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.