A Portrait throughout Perihelion of the NH 2 -rich Interstellar Comet 2I/Borisov

Abstract The interstellar comet 2I/Borisov is the first interstellar object where compositional characterisation was possible throughout its entire perihelion passage. We report all 16 epochs of a comprehensive optical observation campaign with ESO Very Large Telescope’s integral field spectrograph MUSE, spanning 126 days from 2019 November 14 to 2020 March 19. The spatial dust emission of 2I/Borisov was predominantly smooth, with no seasonal effect. A jetlike feature was consistently visible. The gas production morphology of its coma was also smooth and similar for C 2 , NH 2 , and CN: symmetric around the optocentre. The production rates of these species gently declined into and beyond perihelion, until 2I’s outburst and splitting event in early 2020 March. C 2 , NH 2 , and CN production rates all increased, with NH 2 being the most significant; the dust emission also slightly reddened. 2I/Borisov is a carbon-depleted, relatively NH 2 -rich comet when compared to those comets yet measured in the solar system.