Free Astronomy Magazine July-August 2020

17 JULY-AUGUST 2020 SPACE CHRONICLES a comet from outside our solar system,” said astrochemist Martin Cordiner, “and it is dramatically different from most other comets we’ve seen before.” ALMA detected two molecules in the gas ejected by the comet: hy- drogen cyanide (HCN) and carbon monoxide (CO). While the team ex- pected to see HCN, which is present in 2I/Borisov at similar amounts to that found in solar system comets, they were surprised to see large amounts of CO. “The comet must have formed from material very rich in CO ice, which is only present at the lowest temperatures found in space, below -420 degrees Fahrenheit (-250 degrees Celsius),” said planetary scientist Stefanie Milam. “ALMA has been instrumen- tal in transforming our understand- ing of the nature of cometary material in our own solar system – and now with this unique object coming from our next-door neigh- bors. It is only because of ALMA’s unprecedented sensitivity at sub- millimeter wavelengths that we are able to characterize the gas coming out of such unique objects,” said Anthony Remijan of the National Radio Astronomy Observatory in Charlottesville, Virginia, and co-au- thor of the paper. Carbon monoxide is one of the most common molecules in space and is found inside most comets. Yet, there’s a huge variation in the concentration of CO in comets and no one quite knows why. Some of this might be related to where in A rtist impression of the interstel- lar comet 2I/Borisov as it travels through our solar system. This myste- rious visitor from the depths of space is the first conclusively identified comet from another star. The comet consists of a loose agglomeration of ices and dust particles, and is likely no more than 3,200 feet across, about the length of nine football fields. Gas is ejected out of the comet as it ap- proaches the Sun and is heated up. [NRAO/AUI/NSF, S. Dagnello]