New study shows why the Sun’s outer layers are hotter than its surface

A new study may help solve one of astronomy’s oldest puzzles: how the Sun’s outermost layer, the corona, gets hotter than its visible surface. Research points to slow, continuous waves rippling through the solar atmosphere as a possible source of this mysterious heat.

The visible surface of the Sun, known as the photosphere, has a temperature of about 10,000°F (5,500°C). Amazingly, according to NASA, the outer layer, the corona, seen during a solar eclipse can reach 1.8 to 3.6 million°F (1 to 2 million°C) and, in extreme cases, even 72 million°F (40 million°C).

For decades, scientists have wondered how the corona, located far from the Sun’s center, 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 loop, also known as a coronal loop.

These arch-like magnetic structures extend from surface of the sun In corona, further studies found that the waves traveling through them do not dissipate over time. Instead, they remain in place, constantly transferring energy upward.

By examining the polarization of these waves and how they move in three dimensions, the researchers found that most oscillations vibrate in the same direction. This stability indicates that they probably originate from long-term fluxes on the solar surface, which continuously provide energy to the upper atmosphere.

“Our discovery provides important information to answer the long-standing question of what makes hot sun’s corona” said study co-author Valery Nakryakov, a solar physicist at the University of Warwick.

The results show that even weak, sustained waves can carry enough energy to heat the Sun’s corona over time. This breakthrough provides a major step toward understanding not only solar heating, but also the origins of solar flares and other extreme space weather events that can affect Earth.