Roughly halfway between Earth and the Sun, the European Space Agency-led Solar Orbiter spacecraft passed through a very large twist in the solar wind’s magnetic field. Its instruments sampled rare particles inside the structure, allowing researchers to trace the switchback back to the Sun’s surface.
Jesse Coburn, lead author of the research and a researcher at CNRS/LPP in France, said: ‘Solar Orbiter flew through a very large switchback. Because of this, we were able to sample rarely observed particles there that have tell-tale fingerprints of their origin.’
The solar wind is a continuous outflow of hot charged particles, or plasma, from the Sun. It carries the Sun’s magnetic field into space, where the field lines can twist, snap or fold back on themselves as they travel through the Solar System.
These distortions are known as magnetic switchbacks: twists or S-shaped kinks in the solar wind’s magnetic field. In 2022, the European Space Agency reported that Solar Orbiter had seen one such kink. Scientists have long debated how switchbacks form.
During its passage through the large switchback, Solar Orbiter used its Solar Wind Analyser instrument, known as SWA, to examine the plasma. It found a distinctive combination of charged oxygen and carbon particles which could only have formed in hot magnetic loops at the Sun’s surface.
Researchers describe that particle combination as ‘the smoking gun’ for interchange reconnection, a process that occurs when regions of the Sun with different magnetic properties interact. Fingerprinting those elusive particles gave the spacecraft a route from a structure in the solar wind back to its source on the Sun.
The finding adds to efforts to understand solar magnetism, which shapes the Sun’s visible structure and dynamics through its interaction with the plasma of the solar atmosphere. It also offers a clue to processes that can produce disruptive space weather and dangerous storms.
The stakes extend to systems on Earth. Bursts of solar-wind particles can disturb the planet’s protective magnetic field and upper atmosphere, disrupting satellite communications, GPS signals and electrical grids. Large geomagnetic storms can also disrupt radio signals and GPS. Solar activity can produce extreme events including Coronal Mass Ejections that can affect Earth.
Understanding switchbacks and interchange reconnection could help space-weather forecasting and efforts to protect systems vulnerable to solar storms. Scientists had also come closer to identifying the origins of the ‘slow’ solar wind using data from Solar Orbiter’s first close journey to the Sun as of 28 May 2024.
Dr Luca Franci, a Royal Society University Research Fellow at Northumbria University, leads the S³PARK Workshop, which brings together spacecraft instrument teams and early-career researchers studying solar wind and particle physics.
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