Discovery of the First Interstellar Comet and the Spatial Density of Interstellar Objects in the Solar Neighborhood

Abstract— The discovery of the first interstellar comet 2I/Borisov confirmed the astronomers’ speculation that the passage through the solar system of relatively large objects (asteroids and comets) formed outside of it is a common occurrence. There may be many such objects, but their discovery is still a rare case. Large professional telescopes and existing observation programs with these telescopes have limitations that can be overcome with more modest instruments. The paper describes for the first time how comet 2I/Borisov was discovered with the 65-cm telescope designed by G.V. Borisov and those features of the observation program that made it possible to make this discovery. Recommendations are given for constructing future programs for detecting such bodies. The spatial density of interstellar objects (such as asteroid 1I/'Oumuamua or comet 2I/Borisov) in the solar neighborhood has been estimated. According to our estimate, there may be about 50 interstellar bodies >50 m in size in the Solar System in a sphere with a radius of 50 AU at any given time. Since the speeds of possible approach to the Earth of such objects can be very high, such probable approaches require special attention. The use of special space projects for their study is discussed.