The first comet seen visiting our solar system from another star system isn't coming bearing gifts. What comet 2I/Borisov is bringing our way, though, is toxic gas that can be produced from cyanide compounds.
Astronomers reported in a recent issue of the Astrophysical Journal Letters that they'd detected CN gas, which is a molecule of one carbon atom and one nitrogen atom linked together, in the comet's atmosphere.
The discovery doesn't mean intergalactic aliens have launched a cometary canister of tear gas across the cosmos. Rather, it shows that comets from beyond the solar system could be quite similar to the local ones we see all the time, which also bring CN gas with them.
"We could have expected to observe a very different composition, since we don't know the origin and history of this object, which probably wandered for millions of years between the stars before reaching us," the University of Liege's Emmanuël Jehin explained in a statement. "This would indicate that the physical and chemical processes of formation of these small bodies, which are the building blocks of planets and perhaps the source of water and organic material on Earth, would be very common in the galaxy."
The pungent, poisonous gas has been spotted trailing other comets. When Earth was set to drift through the tail of Halley's comet over a century ago, The New York Times quoted a French astronomer saying the comet's tail could "possibly snuff out all life on the planet."
That obviously didn't happen then, as Earth's atmosphere is significant and able to easily disperse the toxic tail of one space rock.
There's far less to worry about this time around because comet Borisov won't be coming particularly close to Earth and will stay beyond the orbit of Mars as it passes through the solar system.
So it's definitely OK to breathe easy as it comes closer over the next several weeks.