... was the first known interstellar object detected passing through the Solar System; hence '1I'. It was discovered by the Canadian astrophysicist Robert Weryk, working on the Pan–STARRS telescope at the Haleakalā Observatory in Hawaii, on 19 October 2017. When it was first observed, it was already heading away from the Sun – having passed closest to it 40 days earlier (on 9 September).
It was first thought to be a comet, but no coma (the nebulous envelope around the nucleus of a comet, formed when the comet warms as it passes close to the Sun, and parts of it sublimate) was observed. It is thought that it could be a remnant of a disintegrated comet that originated outside the Solar System.
The name 'Oumuamua can be translated as 'scout', or (slightly more literally) 'first distant messenger'. ('ou means 'reach out for', and mua, repeated for emphasis, means 'first', or 'in advance of'.) The first character is a Hawaiian 'okina, not an apostrophe (or an unmatched inverted comma!), and is pronounced as a glottal stop.
© Haydn Thompson 2020