• Hubble Observations Show Interstellar Comet 2I/Borisov Rich In Carbon Monoxide (Planetary Science Institute)

Objects colliding a breaking apart is apparently the way of things in our Solar System. We now switch gears to look at the crumbling comet 2I/Borisov. As it passes near our Sun, this interstellar invader has been forming a tail and coma of material that is released as volatiles – all those ices rearing to become gas – sublimate away. On December 15-16, when Borisov was still one object, astronomers used the Atacama Large Millimeter Array to look at the chemical composition of Borisov. These results are now available in the journal Nature, and they show an unusually large amount of carbon monoxide gas and normal amounts of Hydrogen Cyanide. This implies that this comet, which originated in another solar system, must have formed someplace significantly colder than where our solar system’s comets come from.

While it’s not possible to speculate too scientifically about the origins of Borisov, this kind of a composition is consistent with Borisov coming from a solar system with an extremely extended disk, such as those currently being found by ALMA around low mass stars not too different from our sun. Until we find more interstellar comets, we can’t know what is more typical of the universe, comets like those produced in our Solar System, or high CO comets like Borisov. For now, we are going to enjoy Borisov’s shattered departure, and keep looking for more icy alien visitors.