Sunday, June 6, 2021

2I/Borisov comet

The object photographed by the Hubble telescope in this image is a very particular comet: it was in fact the first interstellar comet discovered!

2I/Borisov was named after its discoverer, Russian amateur astronomer Hennadiy Borisov, who first observed it on August 30, 2019. At that moment the comet appeared as a dot of 17th apparent magnitude. 2I/Borisov in the following months continued its journey inside the inner Solar System, until it reached perihelion at 2 AU away from the Sun in December of the same year.

The determination of the orbital parameters clearly showed that the comet does not belong to the Solar System: it moves in a hyperbolic orbit at a speed of 32 km/s. Once it passed perihelion, 2I/Borisov abandoned our Solar System forever.

The study of the comet made it possible to obtain close information on the properties of interstellar objects. The core of the 2I/Borisov was not possible to observe directly as it was hidden by the gas of the coma, but it was possible to indirectly determine its dimensions, which were found to be between 2 and 16 km.

Spectroscopic observations have instead made it possible to determine the composition of the comet. Compounds such as cyanide and molecular carbon have been identified in quantities similar to those found in comets in the Oort Cloud (located in the outer regions of the Solar System). The color of 2I/Borisov was also found to be very similar to that of the long-period comets of the Solar System.

Credit: NASA, ESA, Hubble, D. Jewitt.

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