2IBorisov

2I/Borisov is the second known interstellar object detected passing through the Solar System and the first confirmed object with cometary activity from another star system. It was discovered on 30 August 2019 by Gennadiy Borisov, a Crimean amateur astronomer, using a telescope at the MARGO Observatory in Crimea. Orbital calculations based on astrometric observations showed a hyperbolic trajectory with eccentricity greater than 1, indicating an origin outside the Solar System. The object reached its perihelion in early December 2019 at about 2 astronomical units from the Sun, after which it continued to recede.

Observations during its approach and passage revealed a bright coma and a developing tail, characteristic of comets. Spectroscopic analysis detected common cometary volatiles, including CN and C2, and overall activity consistent with a volatile-rich body. Estimates placed the nucleus size on the order of a few kilometers, with the coma extending to large distances.

2I/Borisov was designated by the International Astronomical Union as 2I/Borisov, and was also cataloged in some records as C/2019 Q4 (Borisov). Its discovery provided the first opportunity to study material from another star system directly and confirmed that interstellar objects can exhibit comet-like activity similar to Solar System bodies. The object continues on a hyperbolic path, leaving the Solar System behind.