Scientists affiliated with India’s Aditya-L1 space observatory have released findings addressing a long-standing puzzle in solar physics: the extreme temperature differential between the Sun’s surface and its outer atmosphere. The Sun’s core reaches approximately 15 million Celsius, while the visible surface measures around 5,500 Celsius. The corona, the outermost layer, maintains temperatures near 2 million Celsius and can spike to 40 million Celsius during periods of heightened activity.
The corona is the source of extreme solar events including flares and coronal mass ejections, or CMEs, which expel enormous quantities of energy into space. During typical solar conditions, the Sun produces two to three CMEs daily, increasing to ten or more per day during peak solar activity cycles that occur every eleven years. This consistent energy loss presents a paradox: if the corona continuously sheds energy without replenishment, the Sun would eventually deplete its reserves, causing catastrophic consequences for Earth.
Research led by Prof R Ramesh of the Indian Institute of Astrophysics identified two energy replenishment mechanisms. The first involves surface convection generating waves that transport energy outward toward the corona, comparable to ocean waves carrying material to shore. The second mechanism involves the Sun’s magnetic field lines, which twist and loop throughout the solar atmosphere. These lines periodically rupture, triggering CMEs, then reconnect and reconfigure, restoring energy to the corona.
Analyzing data from a significant CME recorded on 5 August 2024 using Aditya-L1’s Velc instrument, researchers quantified each mechanism’s contribution. The study determined that surface wave activity supplies only 7 percent of the corona’s energy requirements, while magnetic field line reconfiguration accounts for the remaining 93 percent. The reconnection process occurred within approximately ten hours following the observed CME.
Findings were published in the Astrophysical Journal Letters. Researchers indicated that these measurements establish important reference points for subsequent investigations into solar atmospheric energy generation and may help resolve fundamental questions in physics that challenge conventional understanding.
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