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By comparing our local comet Hale-Bopp with interstellar visitor 2I / Borisov, a team of astronomers has concluded that the intruder is perhaps one of the most pristine comets we have ever seen.
“2I / Borisov could represent the first truly pristine comet ever observed, “ says Stefano Bagnulo of the Armagh Observatory and Planetarium, Northern Ireland, UK, who led the new study recently published in Communications from nature.
Many comets pass through the inner solar system at least once during their lifetime. When they do, they find the solar wind and every other random chunk of microscopic debris floating around. This contaminates them to such a degree that astronomers can determine how many steps a comet has made since it formed.
Comet Hale-Bopp, which wowed stargazers in the late 1990s, was incredibly pure. Astronomers estimated that before its entry in the late 20th century, it had only passed near the sun once before.
Using the FORS2 instrument on the Very Large Telescope of the European Southern Observatory in Chile, a team of astronomers carefully studied interstellar comet 2I / Borisov. That visitor was discovered by amateur astronomer Gennady Borisov in August 2019, and was the second known interstellar intruder in our solar system. The research team found that Borisov and Hale-Bopp were remarkably similar.
“The fact that the two comets are remarkably similar suggests that the environment in which 2I / Borisov originated is not that different in composition from the environment in the early Solar System,” says Alberto Cellino, co-author of the study, from the Astrophysical Observatory. of Turin, National Institute of Astrophysics (INAF), Italy.
Olivier Hainaut, an ESO astronomer in Germany who studies comets and other near-Earth objects but was not involved in this new study, agrees. “The main result, that 2I / Borisov is not like any other comet except Hale-Bopp, is very strong,” he says, adding that “it is very plausible that they formed under very similar conditions.”
2I / Borisov may never have passed near its parent star before being ejected into interstellar space and reaching our own solar system.
“The arrival of 2I / Borisov from interstellar space represented the first opportunity to study the composition of a comet from another planetary system and to see if the material that comes from this comet is in any way different from our native variety”, explains Ludmilla Kolokolova , from the University of Maryland in the USA, who participated in the Nature Communications research.
The truth is, we don’t know much about the life of comets, especially interstellar ones. But future missions can help paint a more complete picture.
Bagnulo hopes astronomers will have another, even better chance to study a rogue comet in detail before the decade is out. “ESA plans to launch Comet Interceptor in 2029, which will have the ability to hit another visiting interstellar object, if one is discovered on a suitable trajectory,” he says, referring to an upcoming European Space Agency mission.
