2I/Borisov, discovered in August 2019 by amateur astronomer Gennady Borisov, was the first confirmed interstellar comet — and the second interstellar visitor ever detected after 1I/ʻOumuamua. It arrived on a hyperbolic trajectory with an eccentricity near 3.4 and a perihelion of 2.0 AU, passing through the inner Solar System before heading back into interstellar space. Spectroscopy revealed a coma rich in cyanide and water, closely resembling Solar System comets. Hubble and ground-based telescopes tracked Borisov from beyond Mars's orbit through perihelion. Its passage confirmed that comets are ejected from planetary systems throughout the galaxy and occasionally wander through ours.