Aditya-L1 sheds light on why Sun's corona is so hot
What's the story
ISRO's Aditya-L1 mission, India's first solar observation project in space, has made significant contributions to understanding one of the most puzzling mysteries in astrophysics: why is the Sun's outer atmosphere (the corona) millions of degrees hotter than its surface? The research was published in the Astrophysical Journal Letters by a team led by Professor R Ramesh from the Indian Institute of Astrophysics (IIA).
Temperature anomaly
Temperature discrepancy across the Sun
The study highlights a major discrepancy in temperature across different layers of the Sun.
The core is around 15 million degrees Celsius, while the surface or photosphere (visible from Earth) is about 5,500°C.
The corona, the Sun's outermost layer, has a temperature of around two million degrees Celsius but can go as high as 40 million degrees Celsius at times.
Professor Ramesh said these temperature variations defy the laws of physics.
Solar phenomena
Corona is also the source of solar flares, CMEs
The corona is also the source of solar flares and coronal mass ejections (CMEs), which release huge amounts of energy into space.
These CMEs can create auroras but also pose a threat to life on Earth by triggering geomagnetic storms that can disrupt power grids and affect weather patterns as well as communication satellites.
During low-activity periods, the Sun releases two to three CMEs daily, but during peak solar activity cycles every 11 years, this number can be over 10.
Energy balance
How does the corona maintain its temperature?
Despite these massive energy losses through CMEs, the Sun doesn't seem to lose its energy and plunge into an irreversible deep freeze.
This led scientists to propose that some "mechanism" is at work to keep the corona's temperature high.
Two main factors are thought to contribute: waves generated by boiling motions on the Sun's surface that carry energy outward and tangled magnetic field lines in its atmosphere that snap and reconnect, replenishing lost energy.
Energy quantification
Study published in Astrophysical Journal Letters
The study led by Professor Ramesh quantified how much energy each of these systems contributes to the corona.
It found that while waves from boiling motions on the Sun's surface contribute only 7% of the energy requirement, a whopping 93% comes from reconfiguring magnetic field lines.
This was determined by analyzing a "very energetic" CME that occurred on August 5, 2024, and was recorded by Aditya-L1's coronagraph VELC (Visible Emission Line Coronagraph).