Reconnection nanojets in an erupting solar filament with unprecedented high speeds

Solar nanojets are small-scale jets generated by component magnetic reconnection, characterized by collimated plasma motion perpendicular to the reconnecting magnetic field lines. As an indicator of nanoflare events, they are believed to play a significant role in coronal heating. Using high-resolution extreme-ultraviolet (EUV) imaging observations from the Extreme Ultraviolet Imager (EUI) onboard the Solar Orbiter mission, we identified 27 nanojets in an erupting filament on September 30, 2024. They are potentially associated with the untwisting of magnetic field lines of the filament. Most nanojets exhibit velocities around 450 km s$^{-1}$, with the fastest reaching approximately 800 km s$^{-1}$, significantly higher than previously reported but comparable to the typical coronal Alfv\'en speed. To our knowledge, these are the highest speeds ever reported for small-scale jets (less than ~1 Mm wide) in the solar atmosphere. Our findings suggest that these nanoflare-type phenomena can be more dynamic than previously recognized and may contribute to the energy release process of solar eruptions and the heating of coronal active regions.