Why the Sun’s atmosphere is hundreds of times hotter than its surface: Aditya-L1 helps solve the Sun's biggest mystery

The Sun appears to break one of nature's most basic rules. Normally, moving away from a heat source should make temperatures fall. Yet the Sun does the opposite. Its visible surface, known as the photosphere, has a temperature of about 5,500°C, while its outer atmosphere, the corona, soars to over 1,000,000 °C.

For decades, this puzzling temperature jump has challenged solar physicists around the world and remains one of the most important unanswered questions in astrophysics. Now, observations from India's Aditya-L1 mission are providing unprecedented views of the layers between the Sun's surface and corona. By tracking how energy moves through the solar atmosphere, the mission is helping scientists investigate the mechanisms that may superheat the corona, bringing researchers closer than ever to understanding one of the Solar System's greatest mysteries.

Why the Sun's atmosphere is hotter than its surface remains one of astronomy's greatest mysteries

At first glance, the Sun's temperature structure seems impossible. The photosphere, which forms the bright surface visible from Earth, is relatively cool compared with the corona above it. Yet measurements show that the corona can reach temperatures exceeding one million kelvin.According to the Indian Space Research Organisation's mission overview:"The corona has a temperature of more than a million degrees Kelvin, which is much higher than the solar disc temperature of around 6000K.

How the corona gets heated to such high temperatures is still an unanswered question in solar physics."Scientists suspect that magnetic fields play a central role. The Sun is a giant ball of electrically charged plasma threaded with powerful magnetic fields. These magnetic structures twist, reconnect and release enormous amounts of energy. Researchers believe that part of this energy is transferred into the corona, causing temperatures to rise dramatically rather than fall with increasing distance from the solar surface.Two leading explanations dominate current research: magnetic reconnection, where tangled magnetic field lines snap and reconnect explosively, and Alfvén waves, magnetic vibrations capable of carrying energy upwards through the solar atmosphere. Determining which process contributes most has remained a major challenge for decades.

How Aditya-L1 is uncovering clues to the mystery of coronal heating

Launched by the Indian Space Research Organisation, Aditya-L1 was specifically designed to study the Sun's atmosphere from the Sun-Earth L1 point, approximately 1.5 million kilometres from Earth.

This location provides an uninterrupted view of the Sun without eclipses or occultations.One of its most important instruments is the Solar Ultraviolet Imaging Telescope (SUIT), which simultaneously observes the photosphere and chromosphere at multiple wavelengths. This capability allows scientists to examine how energy and matter travel between different layers of the solar atmosphere.The SUIT team explains that the instrument was developed to:"Help us understand the processes involved in the transfer of mass and energy from one layer to the other."Recent scientific observations from SUIT have already captured solar flares, ultraviolet plasma eruptions and dynamic atmospheric processes that were previously difficult to observe in such detail. These measurements are providing researchers with valuable evidence about how magnetic energy moves upward from the lower atmosphere towards the corona.

What Aditya-L1's discoveries could reveal about space weather and the future of solar science

Understanding coronal heating is not merely an academic exercise.

The same magnetic processes that heat the corona also drive solar flares, coronal mass ejections and solar storms capable of disrupting satellites, navigation systems, communications networks and power grids on Earth.Aditya-L1’s observations of a Coronal Mass Ejection explicitly include studying:"chromospheric and coronal heating" and the "heat transfer mechanisms" operating within the Sun's atmosphere.By observing the photosphere, chromosphere and corona simultaneously, Aditya-L1 is creating a more complete picture of how energy flows through the Sun.

Scientists hope these observations will eventually reveal why the corona becomes hundreds of times hotter than the surface beneath it and improve predictions of space weather events that affect modern technology.More than a year into its scientific operations, Aditya-L1 is already delivering data that were previously unavailable to researchers. Each new observation brings science a step closer to answering a question that has puzzled astronomers for generations: how can the Sun's atmosphere be hotter than the star that created it?