[Reading Science] 'One Million Degrees Celsius' Solar Corona Mystery Solved

ESA Solar Orbiter Observes High-Energy Magnetic Fields
"Suspected Cause of Corona Temperatures Much Higher Than Surface"

One of the greatest mysteries of the Sun is the enormous temperature difference between its surface and the upper atmosphere, the corona. The corona is located far from the Sun’s core, where hydrogen fusion reactions occur. However, it is much hotter than the surface (6,000 degrees Celsius), reaching temperatures as high as 1 million degrees Celsius. Recently, scientists have detected the presence of high-energy magnetic fields that appear to heat the solar corona, raising hopes of solving this long-standing puzzle.

Sun. Photo by NASA website

A research team from KU Leuven in Belgium announced on the 24th (local time) that they observed the continuous generation of high-energy magnetic fields on the Sun’s surface last October using the Extreme Ultraviolet Imager (EUI) aboard the Solar Orbiter, a spacecraft jointly launched by the European Space Agency (ESA) and NASA. The team’s paper was published the same day in the international astronomy journal, Astrophysical Journal Letters.

The EUI can detect high-energy extreme ultraviolet rays emitted by the Sun. Using this, the team discovered that rapidly moving, swirling magnetic waves about 10,000 km wide were continuously generated on the Sun’s surface. The researchers believe these high-energy magnetic waves are the cause of heating the corona to 1 million degrees Celsius. Their calculations confirmed that these waves produce an enormous amount of energy.

This research result is expected to help solve one of the Sun’s greatest mysteries. Scientists have been trying to identify the cause of the huge temperature difference between the Sun’s surface and corona for over 80 years. Tom Van Doorsselaere, a professor at KU Leuven who participated in the study, stated in a press release, “There is increasing evidence that the Sun’s corona is heated by magnetic fields.”

Previously, another clue to the mystery of the Sun’s corona heating phenomenon was discovered. In July 2020, ESA revealed the first observation images from the Solar Orbiter, showing small fireballs erupting on the Sun’s surface. Although small, these “campfires” ? each about the size of a European country ? were erupting countless times on the Sun’s surface. This means that although the Sun’s surface may appear calm at first glance, small fireballs are constantly exploding.

Launched by ESA in February 2020, the Solar Orbiter can capture images of all wavelengths, including extreme ultraviolet, while approaching the Sun. Although Earth-based telescopes can capture high-resolution images of the Sun, they cannot detect extreme ultraviolet rays because Earth’s atmosphere acts as a filter blocking them. The Solar Orbiter is designed to withstand extreme heat of up to 600 degrees Celsius and orbits about 42 million km from the Sun while conducting observations.

Solar Orbiter jointly launched by ESA and NASA. Photo by ESA website