On the coronal origin of magnetic switchbacks in the solar wind

The Sun continuously releases a stream of charged particles known as the solar wind, threaded by magnetic field lines that occasionally fold back on themselves in sharp reversals called magnetic switchbacks. These structures are frequently observed by spacecraft near the Sun, but their formation mechanism remains an open question. Using measurements from Solar Orbiter at 0.55 AU, we report heavy ion observations within a magnetic switchback that provide direct evidence of its solar source. Elevated charge-state ratios of oxygen and carbon, combined with a depletion of helium relative to protons, indicate that the switchback plasma originated from hot, closed coronal loop structures. A semi-empirical coronal model, constrained by electron temperature and density measurements from the Solar Dynamics Observatory, traces the ion signatures to either a coronal hole boundary or loops within the coronal hole, implicating the source mechanism as interchange reconnection, where closed loops reconnect with open magnetic field and eject plasma. The proton velocity and magnetic field fluctuations of the switchback are in accordance with an outward-propagating Alfvén wave. These findings suggest that interchange reconnection and wave or turbulence mechanisms jointly govern switchback origin and propagation, respectively. Most importantly, we show that switchbacks preserve measurable signatures, carrying information about the physical processes that heat the solar atmosphere and accelerate the solar wind. Solar Orbiter’s detection of the ion composition of a magnetic switchback reveals its origin in hot coronal loops, implicating interchange reconnection as the release mechanism of the solar wind plasma, where it then propagates as an Alfvén wave.