Scientists may be closer to solving one of the Sun’s biggest mysteries: why its outer atmosphere, known as the corona, reaches temperatures of millions of degrees—far hotter than the Sun’s visible surface. Researchers are also investigating how the corona stays so hot despite frequently releasing enormous amounts of energy through solar eruptions.
New observations from Aditya-L1, India’s first space-based solar observatory, have provided important clues about the process that heats the solar corona. The findings, reported by Indian astrophysicists in a recent paper published in the prestigious Astrophysical Journal Letters, could improve scientists’ understanding of solar activity and space weather.
Professor R. Ramesh, a leading solar astrophysicist at the Indian Institute of Astrophysics (IIA) and the study’s lead researcher, said the Sun’s temperature profile appears to challenge conventional expectations about how heat should behave.
The Sun’s core reaches an estimated 15 million degrees Celsius. However, temperatures fall significantly toward the photosphere—the visible surface seen from Earth—which is approximately 5,500 degrees Celsius. Beyond the photosphere lies the corona, the Sun’s outermost atmosphere. Despite being much farther from the core, the corona typically reaches around 2 million degrees Celsius and can become as hot as 40 million degrees Celsius during powerful solar events.
The corona is also where extreme space-weather events, including solar flares and coronal mass ejections (CMEs), occur. These eruptions send vast quantities of energy and charged particles into space. CMEs can create spectacular auroras, but they may also trigger geomagnetic storms that disrupt power grids, satellite operations, communications networks and other technologies on Earth.
During periods of low solar activity, the Sun can produce roughly two or three CMEs each day. At the peak of its approximately 11-year solar cycle, the number of eruptions can rise to more than 10 per day.
“If the Sun loses such enormous amounts of energy during every CME and that energy is not replaced, the star at the centre of our solar system would gradually lose its power,” Professor Ramesh explained. “That could have severe consequences for Earth’s environment.”
Because the Sun continues to shine and the corona remains extremely hot, researchers believe an as-yet-unresolved heating mechanism must continuously replenish the lost energy. Data from Aditya-L1 could help scientists identify that mechanism and finally explain the long-standing mystery of coronal heating.
Source: www.bbc.co.uk