First Determination in the Extended Corona of the 2D Thermal Evolution of a Current Sheet after a Solar Eruption

For the first time the evolution of the coronal reconfiguration after a Coronal Mass Ejection (CME) was observed by the multi-channel Metis Coronagraph on-board the ESA - Solar Orbiter mission. The images acquired in the Visible Light (VL) between 3.0 and 5.4 R_sun show the formation after a CME of a bright elongated radial feature interpreted as a post-CME Current Sheet (CS). This interpretation is supported by the appearance of the same feature as an intensity decrease in the UV Lyman-alpha images. The unique combination of VL and UV images allowed for the first time to map in 2D the time evolution of multiple plasma physical parameters inside and outside the CS region. In particular, the CS electron temperature reached peak values higher than 1 MK, more than 2 times larger than the surrounding corona in the covered altitude range. An elongated vertical diffusion region (DR), characterized as a region of much higher thermal pressure and lower magnetic pressure, is observed to slowly propagate outward during 13 hours of observations. Inside this region the Alfvènic Mach number is on the order of M_A ≃ 0.02 - 0.11, the plasma β is close to unity, and the level of turbulence is higher than the surrounding corona, but decreases slowly with time. All these results provide one of the most complete pictures of these features, and support the idea of a magnetic reconnection coupled with turbulence and occurring in multiple smaller scale CSs resulting in the much broader macroscopic feature observed with the Metis coronagraph. This allows magnetic reconnection to provide a significant heating of the local plasma, despite the weakness of involved coronal magnetic fields in the considered altitude range.