On August 30, 2019, amateur astronomer Gennady Vladimirovich Borisov made an observation in the Crimea with the help of a self-made telescope that may have aroused the jealousy of many professionals: he discovered the comet 2I / Borisov, now named after him. An interstellar visitor on his way through our solar system. This was the second object after asteroid 1I / Oumuamua. Observations with the ESO Very Large Telescope in Chile by a team led by Stefano Bagnolo of the Northern Ireland Planetarium and Armagh Observatory indicate that 2I / Borisov probably did not fly near a star on its long journey. This is what Bagnulo and Co wrote in Nature Communications..
If this finding is confirmed, the Tailed Star will be in its original state practically unchanged, unlike any other comet so far observed. Then it will still consist of the gases and dust that it formed from long ago. For their study, astronomers compared the polar data – that is, the polarization of light waves – from 2I / Borisov with that of comets from our solar system.
The polarization properties of the interstellar visitor differed greatly from all other comets except for Hale-Bopp, which has been very visible with the naked eye since the mid-1990s, even from our latitudes, and has been one of the brightest comets in recent decades. Until the arrival of 2I / Borisov, it was considered the most primitive comet. Before it came back in 1995, it might have passed the sun only once, so the solar wind and radiation had little effect on it. The Hale-Bopp formation was also very similar to that of the gas and dust cloud from which it formed 4.5 billion years ago.
The polarization and color of 2I / Borisov, however, indicate that this comet has changed much less. “The fact that the two comets are remarkably similar indicates that the environment in which 2I / Borisov was formed does not differ much in composition from the environment in the early Solar System,” says co-author Alberto Celino of the Astrophysical Observatory in Turin.
In a second study, a team led by Bin Yang of ESO took a closer look at dust and gas particles from 2I / Borisov. The results are published in the journal Nature Astronomy.. The tailed star coma – the round crust around an actual solid comet nucleus – is made of fragments one millimeter larger and larger. In addition, the comet’s relative proportions of carbon monoxide and water changed as it approached the sun. Scientists write that this indicates that the body was formed from matter that came from different regions of its original system. According to this, some were recorded near the star, and some were in the system. This, in turn, would be an indication for researchers that there must be large gaseous planets there that “excite” the materials and distribute them through their gravity.