In 2017, the first confirmed visitor from another star system tumbled through the solar system on a path that should have been simple to read, then accelerated slightly as it left without showing the coma or tail of an active comet — a gap that let Harvard astronomer Avi Loeb argue it might be alien technology, a claim most astronomers reject but one that has never quite gone away.

In 2017, the first confirmed visitor from another star system tumbled through the solar system on a path that should have been simple to read, then accelerated slightly as it left without showing the coma or tail of an active comet — a gap that let Harvard astronomer Avi Loeb argue it might be alien technology, a claim most astronomers reject but one that has never quite gone away. – Space