Discovery of Small-scale Flows in the Void of a Coronal Mass Ejection with High-cadence Images Acquired by the Metis Coronagraph on Board Solar Orbiter

On 2022 March 26, the ESA Solar Orbiter mission observed the early evolution of a coronal mass ejection (CME). On that day, the spacecraft was at a heliocentric distance of 0.32 au and a longitude separation from Earth of 74 5. The CME source region, observed with the Solar Orbiter Polarimetric and Helioseismic Imager magnetometer, shows no preexisting filament or flux rope. The event was first observed in the inner corona by the Solar Orbiter Extreme Ultraviolet Imager instrument with the Full Sun Imager telescope, showing the initial propagation of a flux rope seen face-on in the EUV, and formed during the eruption. Higher up, the event was observed by Metis with the Visible Light channel with an unprecedented time cadence of 20 s and a spatial resolution of 20" corresponding to about 4600 km bin‑1. The sequence of total brightness images shows the existence of small-scale circular flows inside the expanding flux rope, surrounded by multiple nested arch-shaped features. These motions, never reported so far, occur inside the void of the CME, with projected speed ∼40% higher than the CME propagation speed. The formation of the flux rope during the eruption suggests that these motions can be interpreted as a signature of conversion of magnetic writhe into twist, starting from the shearing of a preexisting arcade.