Key finding: Using the Daniel K. Inouye Solar Telescope, researchers have for the first time detected small-scale torsional Alfvén waves across the solar corona. These twisting waves travel along magnetic field lines and can transport energy and plasma upward from the Sun’s 5,500 °C surface into a corona that reaches millions of degrees. The team removed stronger swaying motions in the data to reveal the torsional signatures, resolving a search that began in the 1940s. The discovery strengthens models of coronal heating and could improve space weather forecasting.
Tiny Twisting Waves May Finally Solve the Sun’s 70‑Year 'Coronal Heating' Mystery
Key finding: Using the Daniel K. Inouye Solar Telescope, researchers have for the first time detected small-scale torsional Alfvén waves across the solar corona. These twisting waves travel along magnetic field lines and can transport energy and plasma upward from the Sun’s 5,500 °C surface into a corona that reaches millions of degrees. The team removed stronger swaying motions in the data to reveal the torsional signatures, resolving a search that began in the 1940s. The discovery strengthens models of coronal heating and could improve space weather forecasting.
16:30, 04.11.2025Science
Small torsional Alfvén waves observed across the corona shed light on how the Sun gets so hot
After decades of debate over why the Sun’s outer atmosphere (the corona) is millions of degrees hotter than its visible surface, an international team of researchers reports the first clear detection of small-scale torsional Alfvén waves throughout the solar corona. The observations, made with the US National Science Foundation’s Daniel K. Inouye Solar Telescope in Hawaii, provide a crucial clue about how energy and plasma move from the Sun’s surface into its ultra-hot outer atmosphere.
What was observed. Torsional Alfvén waves are twisting motions that travel along magnetic field lines while rotating the plasma around them. Until now scientists had mainly observed larger, isolated Alfvén waves associated with flares; smaller, ubiquitous torsional waves had been predicted by theory but not directly seen. Using extremely high-resolution spectral imaging, the team tracked signatures of superheated iron in the corona and identified the telltale Doppler shifts—bluer as material moved toward Earth and redder as it moved away—that reveal twisting motion.
How they found the twisting. Coronal plasma motion is dominated by stronger side-to-side swaying waves that can mask the smaller torsional signal. Researcher Richard Morton of Northumbria University developed a method to remove the swaying component from the data so the twisting became measurable. After separating the motions, the upward-traveling torsional waves were evident across multiple coronal regions.
"This discovery ends a protracted search for these waves that has its origins in the 1940s," says physicist Richard Morton. "We've finally been able to directly observe these torsional motions twisting the magnetic field lines back and forth in the corona."
Why it matters. These small torsional Alfvén waves can transport energy and momentum along magnetic fields, helping to heat coronal plasma and potentially contributing to the acceleration of the solar wind. Better observational constraints on these waves improve theoretical models of coronal heating and Alfvén wave turbulence and can help refine space weather forecasts that protect satellites, communications, and power grids on Earth.
Next steps. With clear detection established, researchers can map the distribution, energy content, and generation mechanisms of these waves across wider coronal regions, and use direct observations to test competing theories of solar heating. The full study is published in Nature Astronomy.
Source: Daniel K. Inouye Solar Telescope observations; research published in Nature Astronomy.