The Sun’s visible surface, known as the photosphere, has a temperature of about 10,000°F (5,500°C). Strangely, the corona, the outer layer seen during solar eclipses, can reach 1.8 to 3.6 million°F (1 to 2 million °C) and, in extreme cases, even up to 72 million°F (40 million°C), according to NASA.
For decades, scientists have wondered how the corona, located farther from the Sun’s core, could be millions of degrees hotter.
The new study focuses on low-amplitude decayless kink oscillations, small, continuous waves that ripple through the Sun’s plasma loops, also called coronal loops.
These arch-like magnetic structures extend from the Sun’s surface into the corona, and the study found that the waves moving through them don’t fade away over time. Instead, they persist, transferring energy steadily upward.
By examining the polarisation of these waves and how they move in three dimensions, researchers discovered that most oscillations vibrate in the same direction. This consistency indicates that they likely stem from long-duration flows on the solar surface, continuously feeding energy into the upper atmosphere.
“Our finding provides important information for answering the long-standing question of what heats the corona of the sun ,” said study co-author Valery Nakariakov, solar physicist at the University of Warwick.
The results suggest that even weak, continuous waves can carry sufficient energy to heat the Sun’s corona over time. The breakthrough provides a major step toward understanding not just solar heating, but also the origins of solar flares and other extreme space weather events that can impact Earth.
