One of the greatest mysteries in solar physics may finally be closer to being solved, thanks to observations from India’s first solar mission, Aditya-L1.
Scientists using data from the spacecraft’s flagship instrument, the Visible Emission Line Coronagraph (VELC), have found strong evidence explaining how the Sun’s outer atmosphere, known as the corona, becomes hundreds of times hotter than its visible surface, a puzzle that has baffled astronomers for decades.
At first glance, the Sun appears to defy common sense. The solar surface, or photosphere, has a temperature of about 5,500 degrees Celsius.
Logically, temperatures should fall as one moves away from the 2 million degrees Celsius and can soar to 40 million degrees during powerful eruptions.
The question of how the corona becomes so extraordinarily hot has remained one of the longest-standing mysteries in astrophysics.
Now, scientists at the Indian Institute of Astrophysics (IIA), Bengaluru, using observations from Aditya-L1, say they have found crucial evidence pointing to the answer.
According to the research team, the primary mechanism responsible for heating the corona is the continuous interaction and reconnection of tangled magnetic fields in the Sun’s atmosphere. These localised magnetic interactions constantly replenish the enormous amount of energy lost during explosive solar events such as solar flares and coronal mass ejections (CMEs).
The findings challenge the long-held view that waves generated by the Sun’s bubbling and boiling surface motions are the dominant ontribute only about seven per cent of the energy required to maintain the corona’s extreme temperatures.
“The results provide an important benchmark for future studies,” said Dr R Ramesh, Senior Professor at IIA and Principal Investigator for VELC. He noted that both waves and magnetic reconnection have long been considered potential heating mechanisms, but the latest observations strongly favour magnetic interactions as the dominant source.
The discovery is significant because the Sun continuously loses vast amounts of energy through eruptions. A single active sunspot region can lose energy at a rate of about one watt per square centimetre, and several coronal mass ejections can occur in a single day. Without a mechanism to replenish this energy, the Sun’s atmosphere would cool dramatically over time.
Scientists say the uninterrupted observations provided by Aditya-L1 from its unique vantage point in space are proving invaluable.
Combined with data from a global network of solar radio spectrographs, including one operated by IIA near Bengaluru, the mission is offering an unprecedented view of the processes powering our nearest star.
The findings, soon to be published in The Astrophysical Journal Letters, mark one of the most important scientific results from Aditya-L1 since its launch and provide a major step toward understanding how the Sun maintains its astonishing energy budget.
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