spaceSpace and Physics

Interstellar Comet Borisov Is More Pristine Than Any Comet We Have Seen Before


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockMar 30 2021, 16:00 UTC
Comet Borisov

Researchers determined that the comet is supremely pristine – probably the most pristine comet that we have ever observed.. Image Credit: ESO/M. Kormesser CC-BY 4.0

Two new studies have provided some incredible insights into the interstellar comet 2I/Borisov which was discovered in August 2019. Thanks to the analysis of its composition, astronomers believe that its foray into the solar system was the first time it ever passed close to a star, and its home planetary system probably houses gas giant planets.

It is truly fantastic that so much can be learned based on what the comet is made of. In the first piece of research, published in Nature Communications, researchers determined that the comet is supremely pristine – probably the most pristine comet that we have ever observed.


The team found remarkable similarities between this object and Comet Hale-Bopp, which was visible to the naked eye from Earth in 1996 and 1997. Scientists believe that Hale-Bopp was only on its second tour of the inner solar system when we saw it, given how pristine and unaltered it was. Comet Borisov is even more pristine, so the researchers of this study believe that it formed in another solar system and was then kicked out without passing close to another star.

“The fact that the two comets are remarkably similar suggests that the environment in which 2I/Borisov originated is not so different in composition from the environment in the early Solar System,” Dr Alberto Cellino, a co-author of the study, from the Astrophysical Observatory of Torino, National Institute for Astrophysics (INAF), Italy, said in a statement.

The observations were possible thanks to the European Southern Observatory’s Very Large Telescope. Another one of ESO’s observatories, the Atacama Large Millimeter/submillimeter Array (ALMA), was used for the second study which was published in Nature Astronomy.


The team led by Dr Bin Yang, an astronomer at ESO in Chile, studied the grains released by the comet as it was heated up by the Sun. As this process took place, the icy nucleus of the comet developed a dusty envelope (the coma). Yang and her team established that the coma was made by compact grains one millimeter (0.04 inches) in size or larger.

The scientists also saw the relative amount of carbon monoxide and water changing as the comet lost layer after layer. This suggested that the comet is made of materials that formed in different places within that star system. The team believes that in the presence of giant planets, stirring with their large gravity, the primordial material could have helped to create this object.

“Imagine how lucky we were that a comet from a system light-years away simply took a trip to our doorstep by chance,” said Yang.


While Comet Borisov was the first interstellar comet, researchers believe that many more will be discovered in the coming years – and the European Space Agency is gearing up to chase one when the occasion arises.

“ESA is planning to launch Comet Interceptor in 2029, which will have the capability of reaching another visiting interstellar object, if one on a suitable trajectory is discovered,” explained lead author Dr Stefano Bagnulo from Armagh Observatory & Planetarium.

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