Aditya-L1 finds magnetic reconnection supplies 93% of corona's heat

Magnetic reconnection supplies 93% of the energy that keeps the Sun's corona at millions of degrees Celsius, while bubbling motions on the solar surface supply just 7%, according to a study published in the Astrophysical Journal Letters.

Led by Prof R Ramesh of the Indian Institute of Astrophysics, the work uses data from India's Aditya-L1 solar mission to explain why the corona — the Sun's outermost layer — remains far hotter than the photosphere and how it recovers after coronal mass ejections.

The corona averages about 2 million Celsius and can spike to 40 million Celsius, compared with about 5,500 Celsius at the photosphere and 15 million Celsius at the core.

Flares and coronal mass ejections originate in the corona and can trigger geomagnetic storms that disrupt power grids, satellites and communications on Earth.

During quiet periods, the Sun launches two to three CMEs a day; during the 11-year solar maximum, it can launch 10 or more. Each event ejects huge amounts of energy, yet the corona does not cool.

Using Aditya-L1's Visible Emission Line Coronagraph (Velc), the team analyzed a very energetic CME on August 5, 2024. Within 10 hours, the tangled magnetic field lines reconnected and restored the corona's energy.

Ramesh said the findings "provide an important benchmark" for future studies of energy generation in the Sun's atmosphere and should help answer fundamental physics questions that currently defy logic.