India's first solar observation mission, Aditya-L1, has yielded new findings that offer vital clues to understanding one of the Sun's most enduring mysteries: how its outer atmosphere, the corona, reaches temperatures millions of degrees Celsius, far exceeding its visible surface. Astrophysicists in India, in a paper published in The Astrophysical Journal Letters, report that the mission's data is helping to unravel why the corona remains so hot despite frequent energy-losing eruptions.
The Sun's temperature gradient is a puzzle. Its core reaches approximately 15 million degrees Celsius, while the visible surface, the photosphere, is around 5,500 degrees Celsius. However, the corona, the outermost layer, can soar to 2 million degrees Celsius or even higher, sometimes reaching up to 40 million degrees Celsius. This extreme temperature variation has long defied conventional understanding.
Solar Eruptions and Energy Balance
These high temperatures in the corona are linked to extreme weather events such as solar flares and coronal mass ejections (CMEs). CMEs release vast amounts of energy into space, which can cause auroras on Earth and also lead to geomagnetic storms. These storms can disrupt power grids, weather forecasting, and communication satellites.
During periods of low solar activity, the Sun releases two to three CMEs daily. This rate can increase to 10 or more per day during the peak of the Sun's 11-year activity cycle. Professor R Ramesh, a leading Indian solar astrophysicist at the Indian Institute of Astrophysics and lead author of the study, noted that if the energy lost through these frequent CMEs were not replenished, the Sun would eventually exhaust its energy, plunging Earth into a deep freeze. The fact that this does not occur indicates a mechanism is at play that sustains the corona's exceptionally high temperature.