(ōmo͞o`əmo͞o`ə), officially 1I/2017 U1 (‘Oumuamua), interstellar object, the first to be discovered in the solar system. Highly variable in brightness, it also is highly and unusually elongated—a cigar-shaped object perhaps as much as 1,300 ft (400 m) long—with a rapid, chaotically tumbling rotation. It appeared to be composed of of rock and metal, indicating that it is an asteroid, but other evidence, such as its reddish outer surface and the speed at which it was moving (which appears not to be explained by the pull of gravity alone, suggesting that ejected gas was also propelling it) suggest it may be a comet. ‘Oumuamua was first observed in Oct., 2017; traveling along a hyperbolic trajectory, it made its closest pass to the sun in Sept., 2017.