Astronomers have spotted signs of water spraying off comet 2I/Borisov, which is flying towards the Sun on a journey from interstellar space. It is the first time scientists have seen water in our Solar System that originated somewhere else.

“There’s water—that’s cool, that’s great,” says Olivier Hainaut, an astronomer at the European Southern Observatory in Garching, Germany. The discovery isn’t surprising, he says, because most comets contain a lot of water. But confirming its presence in an interstellar comet is an important step towards understanding how water might travel between the stars.

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