Solar Orbiter tracks origin of mysterious magnetic switchbacks

The Sun has an intense and restless magnetic field. This field not only governs the star itself but is also dragged outwards along field lines by the solar wind, a stream of hot charged particles (plasma) that continuously pours out from the Sun into space. These lines can twist, snap, or fold back on themselves on their journey through the Solar System. Together, the solar wind and its dynamic field lines create all kinds of exciting activity that we can study to understand what’s happening on and around our star.

Back in 2022, ESA reported that Solar Orbiter had spotted a kink in the solar wind’s magnetic field known as a ‘switchback’. While switchbacks have been spotted often near the Sun, scientists are still debating how they form. By watching from afar, Solar Orbiter helped solve a piece of this puzzle, confirming the switchback to be S-shaped: something scientists had predicted but not seen directly.

The spacecraft has now added another crucial piece to this puzzle by tracing a switchback back to its source at the Sun. “Solar Orbiter flew through a very large switchback,” says Jesse Coburn of CNRS/LPP, France, lead author of the new paper. “Because of this, we were able to sample rarely observed particles there that have tell-tale fingerprints of their origin.”

Not either-or, but both

To make this connection, Jesse and colleagues used Solar Orbiter’s Solar Wind Analyser instrument (SWA) to sample the plasma making up the switchback. At the time, Solar Orbiter was roughly halfway between Earth and the Sun.

They found a mix of charged oxygen and carbon particles that could only have formed in one way: within hot magnetic field loops at the surface of the Sun.

“There are two main competing theories for how a switchback, and by extension the solar wind, forms,” adds Jesse. “The specific mix of particles detected by Solar Orbiter is the smoking gun for a formation process known as 'interchange reconnection’.”

This kind of reconnection takes place when parts of the Sun with different magnetic properties interact. In the Sun’s atmosphere, open regions have field lines that stretch away like highways, allowing material to zoom along them into space. Closed regions have lines that initially extend into space before curving back to the Sun, creating closed loops. When an open region engages with a closed one, the lines can crowd together, snap open, and reconnect in different ways, allowing plasma that was previously trapped in a loop to escape to space.

This is what happened with this switchback – but that’s not all. The alternative theory of switchback formation involves processes related to waves and turbulence (the kind of waves that Solar Orbiter has found to play a key role in heating and accelerating the solar wind).

“Excitingly, we also see signs of these, but likely only after the switchback heads out into space,” says co-author Stephanie Yardley of Northumbria University, UK. “Once the switchback has left the Sun, waves and turbulence take over and govern how it moves.

“Overall, it seems that both processes – interchange reconnection and waves and turbulence – are involved in how switchbacks form and move through space. Our finding reconciles the two, showing that they simply operate at different stages in a switchback’s lifetime.”

From switchbacks to storms

To make the discovery, the researchers studied in situ observations of the switchback’s particles from Solar Orbiter’s SWA, analysed images of the Sun’s disc, and modelled the magnetic fields of both the Sun and surrounding space. They created a new model to identify where the plasma came from; this model connected the measurements from Solar Orbiter to data from NASA’s Solar Dynamics Observatory to reveal the switchback’s solar source in unprecedented detail.

Looking beyond switchbacks, the finding reveals how the Sun heats its atmosphere and accelerates solar wind particles into space. Furthermore, it shows that the Sun’s atmosphere imprints its signature onto the particles making up this wind, giving us a possible way to read the history of solar plasma even far from the Sun.

“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,” says Daniel Müller, ESA Project Scientist for Solar Orbiter. “The more we know, the better we can prepare for solar storms to protect our space-based infrastructure and technology.”

“This discovery just wouldn’t have been possible without Solar Orbiter – no other spacecraft has both the proximity to the Sun and the right instruments needed to make this connection. It’s a great example of the mission delivering exactly the kind of science we knew it could, connecting the Sun to its wider environment and revealing more detail about our star.”

Notes for Editors

‘On the Coronal Origin of Magnetic Switchbacks in the Solar Wind’ by Jesse T. Coburn et al. is published today in Nature Astronomy. DOI: 10.1038/s41550-026-02928-0

More about Solar Orbiter: https://www.esa.int/Science_Exploration/Solar_Orbiter

For more information, please contact

ESA Media Relations, media@esa.int