The team analyzed measurements taken by Solar Orbiter on 2 March 2022, when the spacecraft was roughly 0.55 astronomical units from the Sun, about 120 solar radii. During a six-hour window, the spacecraft recorded five intervals in which the radial component of the magnetic field reversed direction. Crucially, the suprathermal electron beam, the population of energetic electrons that streams away from the Sun along magnetic field lines, continued to point sunward throughout these reversals. That detail matters enormously: if the field had genuinely flipped its polarity, the electron beam would have reversed too. Instead, the field was folded back on itself, the defining signature of a switchback rather than a true sector boundary crossing.

What elevates this event from another statistical entry in the switchback catalog is the heavy ion data. Solar Orbiter’s Solar Wind Analyser, equipped with a Heavy Ion Sensor, measured the charge states of oxygen and carbon ions within and around the switchback. The ratios of O7+ to O6+, C6+ to C4+, and C6+ to C5+ all rose sharply and simultaneously with the largest switchback, which spanned from roughly 20:25 to 21:55 UTC. Because ions freeze in their charge state once the coronal density drops too low for further ionization or recombination, these ratios act as a fossil thermometer, recording the electron temperature of the plasma’s source region millions of kilometers back along the solar wind stream.

The elevated charge-state ratios pointed to a source region far hotter than the typical open magnetic field of a coronal hole. Adding to the picture, the ratio of helium ions to protons dropped measurably inside the switchback. Helium depletion is a well-known signature of plasma that has spent time on closed coronal loops, where wave heating and collisional transport fractionate elements differently than on open field lines. Taken together, the hot ion charge states and the helium deficit indicated that the switchback plasma had originated in hot, closed magnetic loop structures rather than in the cooler, open flux of the coronal hole itself.

To pin down the source more precisely, the researchers combined magnetic field modeling with remote sensing. Using a potential field source surface model coupled to a Parker spiral, they back-traced the field lines connecting Solar Orbiter to the solar surface, testing source surface heights between 1.5 and 3 solar radii. The footpoints converged on a large equatorial coronal hole, consistent with earlier connectivity studies for this period. Meanwhile, the Solar Dynamics Observatory’s Atmospheric Imaging Assembly imaged the same portion of the Sun in six extreme ultraviolet passbands, allowing the team to apply a differential emission measure technique and extract the most probable electron temperature and density of the low corona at the connected footpoints.

Those remote measurements then fed a semi-empirical coronal model. The team set the measured temperature and density, around 1.1 to 1.2 million kelvin, as the lower boundary condition of a coronal hole flux tube model and solved the non-equilibrium ionization equation outward through the corona, using ionization and recombination rates from the CHIANTI atomic database. The predicted frozen-in charge-state ratios matched the values Solar Orbiter measured at the peak of the switchback. Mapping the model across every pixel of the solar image revealed two candidate source regions: the boundary of the coronal hole, or small magnetic loops embedded within the coronal hole itself. Applying a constant-pressure scaling law, the team estimated the loop lengths at roughly 8 to 12 megameters, about a third of a supergranule, consistent with the observed size of coronal bright points.

The physical interpretation that emerges is interchange reconnection. In this process, closed magnetic loops carrying hot plasma reconnect with open field lines of the coronal hole, releasing the loop plasma into the solar wind and exchanging the connectivity of the field. The hot, helium-depleted plasma measured inside the switchback is exactly what interchange reconnection would deliver, and the mechanism has previously been invoked to explain the fast solar wind emerging from coronal holes. The loop sizes found here, tens of megameters, align with models in which interchange reconnection injects both energy and mass into the corona to create the solar wind.

Yet the story does not end at the Sun. The team also examined how the switchback propagated through interplanetary space. Inside the major switchback, the radial proton speed increased by approximately 50 kilometers per second, nearly equal to the local Alfvén speed, while the magnetic field strength remained roughly constant. The relative drift speeds between heavy ions and protons changed sign across the switchback boundaries, with all differences remaining below the local Alfvén speed. These observations are broadly consistent with an outward-propagating, large-amplitude, spherically polarized Alfvén-like fluctuation, suggesting that once launched by reconnection, the switchback travels outward as a wave-like structure, riding on the solar wind at roughly the Alfvén speed above the bulk flow.

This dual character, a reconnection birth and an Alfvénic propagation, is perhaps the study’s most consequential message. The solar physics community has long been split between two paradigms for heating the corona and accelerating the solar wind: reconnection on one side, and waves and turbulence on the other. The new results suggest these mechanisms are not mutually exclusive competitors but partners in a single system. Interchange reconnection appears to govern where and how switchback plasma is released from the corona, while wave and turbulence physics governs how the resulting structures propagate and evolve. Switchbacks, in this view, are a living demonstration of the elaborate interplay between the two mechanisms.

The authors caution that this is a single case study, and that the analyzed switchback was unusually long-lived compared with the typical duration distribution. Larger statistical surveys, including intervals with multiple coronal holes on the solar disk and future missions carrying more capable heavy ion instrumentation, will be needed to establish how often switchbacks preserve their coronal fingerprints. Still, the implications are striking. If switchbacks reliably retain measurable signatures of their source, they become messengers from regions of the solar atmosphere that are extraordinarily difficult to observe directly, encoding information about heating in the chromosphere and corona, kinetic energization of ions, and the fundamental energy transfer processes that drive the solar wind. Tracing these folded field lines from the photosphere, where the energy input begins, to the point where spacecraft intercept them may finally allow scientists to quantify the balance between reconnection and turbulence that powers our star’s ever-flowing wind.

Subject of Research: The coronal origin of magnetic switchbacks in the solar wind traced by Solar Orbiter heavy ion observations

Article Title: On the coronal origin of magnetic switchbacks in the solar wind

Article References: Coburn, J. T., Yardley, S. L., Ngampoopun, N., Dewey, R., Rivera, Y. J., De Marco, R., Verscharen, D., Owen, C. J., Suen, G. H. H., Alterman, B., Baker, D., Fazakerley, A., Galvin, A. B., He, J., Horbury, T. S., Hou, C., Ioannou, C., Kistler, L. M., Lepri, S. T., … Rouillard, A. P. (2026). On the coronal origin of magnetic switchbacks in the solar wind. Nature Astronomy. https://doi.org/10.1038/s41550-026-02928-0

Image Credits: AI Generated

DOI: 10.1038/s41550-026-02928-0

Keywords: solar wind, magnetic switchbacks, Solar Orbiter, corona, interchange reconnection, Alfvén waves, heavy ions, charge states, coronal holes, coronal loops, heliophysics, Nature Astronomy