Free Astronomy Magazine July-August 2021

43 JULY-AUGUST 2021 ASTRO PUBLISHING ago. By analysing the polarisation to- gether with the colour of the comet to gather clues on its composition, the team concluded that 2I/Borisov is in fact even more pristine than Hale– Bopp. This means it carries untar- nished signatures of the cloud of gas and dust it formed from. “The fact that the two comets are remarkably similar suggests that the environ- ment in which 2I/Borisov originated is not so different in composition from the environment in the early Solar System,” says Alberto Cellino, a co-author of the study, from the As- trophysical Observatory of Torino, National Institute for Astrophysics (INAF), Italy. Olivier Hainaut, an as- tronomer at ESO 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 they formed in very similar conditions.” “The arrival of 2I/Borisov from inter- stellar space represented the first op- portunity to study the composition of a comet from another planetary sys- tem and check if the material that comes from this comet is somehow different from our native variety,” explains Ludmilla Kolokolova, of the University of Maryland in the US, who was involved in the Nature Communications research. Bagnulo hopes astronomers will have an- other, even better, opportunity to study a rogue comet in detail before the end of the decade. “ESA is plan- ning to launch Comet Interceptor in 2029, which will have the capability of reaching another visiting inter- stellar object, if one on a suitable tra- jectory is discovered,” he says, refer- ring to an upcoming mission by the European Space Agency. !