By the time we realised that there was an extrasolar intruder, 'Oumuamua, named after the Hawaiian word for "scout", had already passed its closest point to the Sun and was leaving, as fast and stealthily as it had arrived. We are talking about the first sighting, in 2017, of an asteroid-like object from another area of the galaxy, a messenger from distant worlds. What do we know about this dark, probably cigar-shaped shard, which visited our Solar System with a trajectory and velocity that allowed it to leave so quickly?

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