Findings from India's Aditya-L1 solar mission suggest how the Sun maintains its extreme coronal temperatures despite constant energy loss.

Data from India's first solar observation mission, Aditya-L1, has provided scientists with new insights into why the Sun's outer atmosphere, the corona, remains significantly hotter than its surface. A study led by Prof. R. Ramesh of the Indian Institute of Astrophysics, published in the Astrophysical Journal Letters, identifies the primary mechanism responsible for replenishing the energy lost during solar eruptions.

The Coronal Temperature Paradox

The Sun's temperature profile presents a long-standing challenge to physics. While the core reaches 15 million degrees Celsius, the surface temperature drops to approximately 5,500 degrees Celsius. In contrast, the corona—the outermost layer—reaches temperatures between 2 million and 40 million degrees Celsius. This region is the source of solar flares and coronal mass ejections (CMEs), which release massive amounts of energy into space.

Energy Replenishment Mechanisms

The study examined two primary factors that supply energy to the corona. The first involves waves generated by bubbling motions on the Sun's surface, which transport energy outward. The second involves the snapping and reconnection of tangled magnetic field lines in the Sun's atmosphere. When these lines rupture, they trigger CMEs, but their subsequent reconnection allows the Sun to replenish lost energy within hours. Researchers quantified the contribution of these two systems, finding that the magnetic reconnection process is the dominant source of energy. While surface-generated waves contribute only 7% of the energy required to maintain the corona's temperature, the reconfiguration of magnetic field lines supplies the remaining 93%.