The Sun's outer atmosphere is hundreds of times hotter than its surface.

The 'coronal heating problem' has puzzled astronomers since the 1940s when researchers like Bengt Edlén and Hannes Alfvén first identified high-temperature emission lines in the solar spectrum. The Sun's visible surface, the photosphere, maintains a temperature of approximately 5,500°C (10,000°F). However, the corona, which extends millions of miles into space, regularly exceeds 1.1 million degrees Celsius (2 million degrees Fahrenheit).This temperature inversion contradicts the Second Law of Thermodynamics, which suggests heat should dissipate as it moves away from the core. To solve this, NASA's Parker Solar Probe and the European Space Agency's Solar Orbiter have been studying two primary theories: magnetic reconnection and wave heating. Magnetic reconnection occurs when magnetic field lines in the solar plasma snap and realign, releasing massive bursts of energy known as nanoflares.Each nanoflare is equivalent to a 10-megaton hydrogen bomb, and millions occur every second across the Sun. Another contributor is 'Alfvén waves,' which are magnetic oscillations that carry energy from the Sun's interior up into the atmosphere. These waves dump their energy into the corona, accelerating particles and raising temperatures to extreme levels. Understanding this process is vital for predicting space weather, which can disrupt satellite communications and power grids on Earth.