Metis observes the Sun’s corona
The outer atmosphere of the Sun, known as the corona, can be seen stretching off into space in this image from Solar Orbiter’s Metis instrument. Metis is a multi-wavelength device, working at visible and ultraviolet wavelengths. It is a coronagraph, which means that it blocks out the bright sunlight of the solar surface, leaving the fainter light that scatters off the particles in the corona visible. In this image, the fuzzy red disc represents the coronagraph while the white disc is a mask to compress the image size to reduce the amount of unnecessary data downlinked.
There is an enduring mystery surrounding the corona: its temperature. Composed of a magnetised gas called a plasma, the corona has a temperature of around a million degrees Celsius but it cannot be heated from the much cooler solar surface. Solar physicists have long suspected that turbulence must be involved but gathering the necessary measurements to investigate this hypothesis has been difficult. Recently an opportunity became available.
On 1 June 2022, the ESA-led Solar Orbiter spacecraft was turned slightly and rolled to one side, so that Metis could see the part of the corona through which NASA’s Parker Solar Probe was flying. This manoeuvre meant that for the first time, solar physicists recorded both the in-situ behaviour of the plasma in the solar corona, and the large-scale consequences. This enabled them to make the first combined estimate of the coronal heating rate. The results provide strong evidence that turbulence in the magnetised plasma is indeed causing the extraordinary heating.
