Studies into the composition of first interstellar comet shed light on its formation

An international team of researchers studied the composition of the first interstellar comet 2I/Borisov with the Very Large Telescope in Chile. They found that its composition is very similar to that of solar system comets, indicating that it might have formed in an environment similar to that in which solar system comets rich in carbon monoxide form.

2I/Borisov was discovered in August 2019 by amateur astronomer Gennady Borisov. It was soon after confirmed that the comet did not come from our own solar system, but was an interstellar interloper formed around another star.  Comets are some of the most pristine relics of the planetary formation process and their ices still contain information about the conditions that were prevailing at the time planets were forming. 2I/Borisov is the first interstellar comet that we had the chance to observe. It allowed us to probe material that formed around another star for the first time and to investigate how different formation conditions might influence the composition of comets.

Because of this exciting new opportunity, 2I/Borisov was observed with numerous telescopes around the globe and in space for several months. Most of these observations focused on the cloud of dust and gas surrounding the nucleus of the comet (called the coma) resulting from the sublimation of the cometary ices. We observed the interstellar comet for four months with the UVES instrument  at the Very Large Telescope, operated by the European Southern Observatory in Chile to constrain the composition of its coma. The research was led by Cyrielle Opitom, Chancellor Fellow at the School’s Institute for Astronomy, in collaboration with Colin Snodgrass from the IfA and researchers from several institutes in Europe, the US, and Japan. After a careful processing of the observations, we detected several atoms or molecules, such as CN, C2, NH, CH, O, and even the metals Fe and Ni. These enabled the first determination of key quantities potentially sensitive to the formation conditions of interstellar comets, such as the ratio between the Fe and Ni abundances. We found that, except for the high carbon monoxide abundance that was reported from previous studies, 2I/Borisov is surprisingly similar to solar system comets in terms of the composition of its ices. This could indicate that the first interstellar comet formed in a cold environment similar to the formation environment of carbon monoxide-rich solar system comets.

Dr Cyrielle Opitom commented: 

This is very exciting to have the opportunity to probe ices from a comet formed around another star for the first time and see that they are surprisingly similar to ices in comets from our own solar system.