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2I/Borisov is an interstellar object discovered in 2019, essentially a comet en route to pass through the solar system. It is the second such passing interstellar object identified (indicated in the designator by the "2I"), the first being 1I/'Oumuamua in 2017 and later a third, 3I/ATLAS in 2025. Such objects are identified by their speed and orbital path: the speed is too great for a body orbiting the Sun, i.e., more than the Sun's escape velocity, and its path is hyperbolic rather than elliptical. 2I/Borisov's eccentricity was 3.3565, substantially greater than 1, the limit on an elliptical orbit. It was spotted 3 AU from the Sun, i.e., within Jupiter's orbit. Its closest approach to the Sun was about 1.9 AU in December 2019.