?Oumuamua ?mo?o?mo?o? [key], 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 suggests it might be cometlike, 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, but no evidence of such gases were recorded). Other researchers have suggested that it may be a piece of planet destroyed by a star's gravity, or a block of frozen hydrogen formed in the core of an interstellar cloud. ?Oumuamua was first observed in Oct., 2017; traveling along a hyperbolic trajectory, it made its closest pass to the sun in Sept., 2017.

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