Indian solar mission's new findings throw light on enduring Sun mysteries

One of the enduring mysteries that has puzzled scientists for a long time is why the Sun's outer atmosphere, known as the corona, is significantly hotter than its surface. Additionally, how does the corona maintain its high temperature despite frequent eruptions that release large amounts of energy? Indian astrophysicists have made some important discoveries about the Sun using the Aditya-L1, India's first solar observation mission in space.

Their findings are detailed in a recent paper published in the prestigious Astrophysical Journal Letters. The temperature of the Sun varies in different regions, defying the laws of physics. The core of the Sun, which is deep inside and very hot at 15 million degrees Celsius, contrasts with the surface or photosphere at around 5,500 degrees Celsius.

The corona, the Sun's outermost layer, has temperatures reaching up to 2 million Celsius, occasionally rising to 40 million Celsius. This layer is where extreme weather events, such as solar flares and coronal mass ejections (CMEs), originate. These events release large amounts of energy into space and can cause beautiful auroras on Earth, but they can also disrupt power grids, affect weather, and impact communication satellites.

During low solar activity, the Sun releases two to three CMEs daily, while during peak solar activity, this number can increase to 10 or more in a single day. The Sun's core, at 15 million degrees Celsius, is where the energy originates, but as it travels outwards, it loses energy. However, despite losing this energy, the corona remains extremely hot, a mystery that Indian astrophysicists aim to solve.

Two factors are believed to contribute to maintaining the corona's high temperature: the bubbling and boiling motions on the Sun's surface that generate waves, and the tangled magnetic field lines in the Sun's atmosphere that frequently snap and reconnect. While the former contributes only 7% of the energy needed, it is the latter that supplies the remaining 93%.

By analyzing a significant CME that occurred on August 5, 2024, Prof Ramesh and his team discovered that the magnetic field lines reconnecting and returning to their original positions replenish the lost energy in the corona. This study provides a benchmark for future research into the mechanisms that generate energy in the Sun's atmosphere, potentially shedding light on fundamental physics questions that seem illogical.