Flying halfway between Earth and the Sun, the Solar Orbiter spacecraft passed directly through an S-shaped magnetic switchback and traced its origins to hot solar surface loops. The findings reconcile competing theories on solar wind formation, providing researchers with new tools to study space weather and protect infrastructure.
The Sun’s magnetic field constantly sends streams of charged particles into the heliosphere via the solar wind. Within these streams, scientists have frequently encountered mysterious S-shaped kinks known as switchbacks, where the field abruptly folds back on its path before snapping forward again. While these structures were first revealed in detail by NASA’s Parker Solar Probe as common features of the near-Sun environment, their precise origins remained unproven as researchers debated competing formation theories.
In 2022, the European Space Agency-led Solar Orbiter captured an observational milestone by spotting an S-shaped kink from a distance, confirming through direct imaging that the theoretical structures genuinely possess that geometry. The spacecraft has now gone a step further by flying directly through a very large switchback while positioned roughly halfway between Earth and the Sun, measuring the plasma contained inside the bend to read its chemical signature. The paper, On the Coronal Origin of Magnetic Switchbacks in the Solar Wind,
is published in Nature Astronomy (DOI: 10.1038/s41550-026-02928-0).
Sampling Heavy Ions With the Solar Wind Analyser
Researchers used the spacecraft’s Solar Wind Analyser instrument to examine the plasma making up the structure. The instrument measured heavy ions inside the disturbance, specifically tracking the charge states of oxygen and carbon.
An ion’s charge state depends on how many electrons it has lost, functioning like a thermal thermometer recording the environment where the particles originally forged their chemical identity.
The analysis revealed a distinctive mix of charged oxygen and carbon particles trapped inside the S-shaped kink. According to findings published in Nature Astronomy, that specific combination could only have developed within hot, closed magnetic loops anchored to the Sun’s surface. Researchers combined these direct particle measurements with solar disk images and coronal modeling, linking Solar Orbiter’s telemetry to data from NASA’s Solar Dynamics Observatory to map the exact solar source region in unprecedented detail. For this purpose, the group constructed a semi-empirical coronal model using electron temperature and density readings supplied by NASA’s Solar Dynamics Observatory. The plasma was traced by the analysis back to magnetic loops inside a coronal hole or a coronal-hole boundary.
“Because of this, we were able to sample rarely observed particles there that have tell-tale fingerprints of their origin.”
Jesse Coburn, researcher at CNRS and the Laboratoire de Physique des Plasmas
Interchange Reconnection Unites Theories on Switchback Formation
Heliophysicists divided into two primary camps regarding how switchbacks form. One group argued that switchbacks are born at the solar surface when magnetic structures snap and reconnect. The other camp maintained that the kinks form along the journey as waves and turbulence bend the magnetic field while the solar wind streams outward.
The detection of loop-origin ions provides the evidence needed to unite these schools of thought. Investigators identified interchange reconnection—a process where open magnetic field lines interact and reconnect with closed magnetic loops—as the trigger that releases trapped plasma into space and forms the switchback. Headed by Jesse Coburn of France’s CNRS and the Laboratoire de Physique des Plasmas (LPP), the study also features Stephanie Yardley of Northumbria University in the UK as a co-author.
“The specific mix of particles detected by Solar Orbiter is the smoking gun for a formation process known as ‘interchange reconnection’.”
Jesse Coburn, lead author of the study
The research acknowledges the validity of the second theory by establishing a chronological timeline. Once the switchback escapes the Sun and enters open space, physical forces change.
“Our finding reconciles the two, showing that they simply operate at different stages in a switchback’s lifetime.”
Jesse Coburn, lead author of the study
Waves and turbulence take over once the structure departs the solar atmosphere, governing how the disturbance moves through the heliosphere toward the outer planets. According to Stephanie Yardley, waves and turbulence assume control over the switchback’s trajectory through space once it has left the immediate solar vicinity.
Solar Plasma Discoveries Improve Space Weather Predictive Models
The discovery offers a method for reading the history of solar plasma even far from its birthplace. By understanding how the Sun heats its corona to millions of degrees and accelerates particles into the solar wind, scientists gain visibility into the primary drivers behind dangerous solar storms that threaten Earth.
Space weather events pose hazards to satellites, power grids, and communication networks operating in Earth orbit and beyond. Researchers emphasize that connecting surface dynamics directly to heliospheric measurements strengthens predictive models for these phenomena. Daniel Müller emphasized this connection, highlighting that no other spacecraft possesses both the proximity to the sun and the right instruments needed to make this connection.
“As humans on Earth – and in space – our lives are entangled with what’s happening on our star. The solar wind ties the Earth to the Sun, and our understanding of its dynamics has key implications for how we keep our planet safe from extreme space weather events.”
Daniel Müller, European Space Agency project scientist for Solar Orbiter
As solar activity continues through the current cycle, mission scientists note that capturing additional close-range encounters with heavy-ion instrumentation will be essential to determine whether interchange reconnection dictates the genesis of every observed switchback across the heliosphere.