ESO/K. Meech et al.
On September 9, 2017, a rocky, elongated body visited our solar system from beyond the realms of the Sun — the first-ever recorded interstellar object to cruise through our part of the galaxy.
'Oumuamua was like nothing astronomers have observed before, not quite a comet nor an asteroid. They could not agree on where it came from or what it was made of.
They still can't.