The Hubble Space Telescope received new images of Borisov’s interstellar comet before and after perihelion. It turned out that the comet’s nucleus is more than 15 times smaller than originally thought, and its radius is less than 500 meters, according to the NASA website.

Comet 2I / Borisov was discovered on August 30, 2019, by the astronomer Gennady Borisov, and it soon became clear that its orbit has an eccentricity of more than three. The comet turned out to be the second interstellar object known after the asteroid 1I / Oumuamua: it moves in a hyperbolic orbit and can leave the solar system – and very soon. 

2I / Borisov studies can provide information on the composition of protoplanetary disks around other stars and the characteristics of planetesimals, so the comet is now monitored by a lot of terrestrial and space telescopes. Astronomers, for example, have already determined that a comet is very similar to similar objects in the solar system, measured the length of its tail, and also detected the outflow of cyan molecules and estimated the rate of loss of water from the surface of its core. 

2I / Borisov was also studied according to the data from the Hubble telescope: with its help it was possible to obtain the most detailed image of the body. The task of new observations was to compare the parameters of the coma and nucleus before and after approaching the Sun: the Hubble data show a change in the size of the comet’s coma, as well as a change in the direction of its tail. In addition, it turned out that the nucleus of Borisov’s comet is more than 15 times smaller than originally thought, and its radius is less than 500 meters.

The first necessary Hubble image was received on November 16, 2019, when the comet was at a distance of 326 million kilometres from the Earth, and there were 23 days left until the perihelion passed. The image also hit the distant spiral galaxy 2MASX J10500165-0152029. The telescope took the second picture on December 9, after the comet passed the perihelion of its orbit: at that moment it was located at a distance of 297 million kilometres from the Earth, at the inner border of the Main Asteroid Belt. The color of the comet’s coma in the images is artificial and is necessary to identify small details in it.

The parameters obtained for the cometary nucleus are rather unusual and allow us to estimate how often such objects can be registered in the solar system in general. It is expected that by mid-2020, Borisov’s comet will cross the orbit of Jupiter and after a while will return to interstellar space.