Indian solar mission’s new findings throw light on enduring Sun mysteries
Aditya-L1 Data Reveals How the Sun Maintains Its Scorching Corona
Ninoda.com – One of astronomy's longest-standing puzzles concerns the Sun's outer atmosphere. Scientists have long wondered how the corona reaches temperatures millions of degrees above the surface, and what keeps it so hot even after massive energy losses during eruptions. New research from India's Aditya-L1 mission may finally provide answers.
Published in the Astrophysical Journal Letters, the study led by Professor R Ramesh of the Indian Institute of Astrophysics offers crucial insights into these phenomena. According to Prof Ramesh, the temperature patterns observed across various solar regions challenge conventional understanding.
Understanding Solar Layers and Temperatures
Examining the Sun from its center outward reveals dramatic temperature shifts. The core burns at approximately 15 million degrees Celsius. Moving to the photosphere—the visible surface we observe from Earth—temperatures drop to around 5,500 degrees Celsius. Yet the corona, the outermost layer, soars to roughly 2 million degrees Celsius and can occasionally reach 40 million degrees Celsius.
This extreme outer region serves as the birthplace for powerful solar events. Solar flares and coronal mass ejections, collectively known as CMEs, originate here and release enormous quantities of energy into space. These eruptions create spectacular auroras on Earth while simultaneously posing risks to power infrastructure, weather systems, and communication satellites through geomagnetic storms.
The Energy Mystery Solved
The frequency of CMEs varies considerably throughout the solar cycle. During periods of normal activity, the Sun produces two to three such events daily. However, during peak solar activity—which recurs every eleven years—ten or more CMEs can occur in a single day.
"Now if the Sun is losing such huge amounts of energy with each CME and it's not replenished, the star at the centre of our solar system would lose all its energy and Earth would plunge into an irreversible deep freeze," Prof Ramesh explains.
Since this catastrophic scenario does not occur, researchers concluded that some mechanism must continuously restore the corona's heat. Two primary processes contribute to this energy replenishment.
The first involves turbulent, boiling movements on the solar surface that generate waves. As these waves travel outward, they transport energy toward the corona, similar to how ocean waves carry foam toward the shoreline. The second mechanism involves magnetic field lines within the Sun's atmosphere that constantly break apart and reform.
When these twisted, looping magnetic structures—resembling braided strands—rupture, they trigger CMEs. These eruptions typically emerge near sunspots, which appear as darker, cooler regions where magnetic fields intensify. After a CME occurs, the magnetic lines reconnect, allowing the Sun to restore lost energy within hours.
Quantifying the Energy Sources
The research team calculated the precise energy contribution from each mechanism. Their analysis demonstrates that magnetic field reconnection provides the overwhelming majority of energy needed to sustain the corona's temperature.
"Though the waves generated as a result of the bubbling, boiling motions on the Sun's surface generate and transport energy, their contribution is very little - they supply only 7% of the energy requirement."
"The remaining 93% comes because the Sun reconfigures itself and replenishes the lost energy."
To reach these conclusions, Prof Ramesh and colleagues examined a particularly powerful CME that occurred on August 5, 2024. Data captured by Aditya-L1's Velc instrument—short for Visible Emission Line Coronagraph—revealed critical details about the event.
"We saw that in 10 hours after the CME, the tangled field lines were able to go back to their original place, they reconnected and corona's energy was reconfigured," he said.
The corona remains visible to human eyes only during total solar eclipses, making such missions essential for continuous observation. India's solar exploration program continues to yield valuable discoveries about our nearest star.
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