From solar wind to turbulence
The solar wind is an incessant flow of charged particles from the Sun. As solar wind particles move through space they create a chaotic motion called turbulence. Images obtained with the Metis coronagraph, an optical instrument for observing the Sun's corona, confirm what has long been suspected: the turbulent motion of the solar wind begins very close to the Sun, inside the solar corona (the outermost layer of the Sun's atmosphere). The disturbances affecting the solar wind in the corona are then transmitted outwards and spread, generating a turbulent flow all the way to the space between the planets.
Turbulence affects how the solar wind is heated, how it moves through the solar system and how it interacts with the magnetic fields of the planets it passes through. Understanding solar wind turbulence is essential for predicting space weather and its effects on Earth.
The Metis coronagraph on board the Solar Orbiter spacecraft: a key instrument in this discovery
By blocking direct sunlight, the Metis coronagraph is able to capture light at different frequencies from the solar corona. Its high-resolution, high-speed images show the detailed movement of solar plasma within the corona. This reveals how the solar wind is already becoming turbulent at its roots. The images obtained by the team led by Daniele Telloni (INAF, Turin) made it possible to observe in detail the propagation of turbulence from the solar corona into interplanetary space, as shown in the video animation below.
The red-tinted ring shows observations taken by Metis in October 2022. At that time, the Solar Orbiter probe was only 43.4 million km from the Sun, less than a third of the distance Sun-Earth. Changes in the luminosity of the Sun's corona are directly linked to the density of charged particles within it. These changes are made visible by subtracting consecutive images of coronal luminosity taken two minutes apart. This reveals how the charged particles of the solar wind within the corona move chaotically and turbulently.
