On Oct. 19, 2017, a telescope in Maui detected something that had entered our solar system from elsewhere in the galaxy. Astronomers named it Oumuamua, Hawaiian for “scout” or “messenger,” because it was the first interstellar object they had ever recorded — the only known traveler to have crossed the vast distance between another star system and our own. Where it came from was only part of its mystery. Oumuamua fit none of the well-understood astronomical categories. If it was a rock — an asteroid — it was an extremely strange one. Researchers estimated that it was at least the length of a football field; its shape was hard to determine, but it seemed to be long and thin, like a cigar. “No known objects in the Solar System have such extreme dimensions,” wrote the group of astronomers who discovered the object.
