’OUMUAMUA, an object tumbling through space that was discovered on October 19th, has already made history. The speed at which it is moving relative to the sun means that it cannot be native to the solar system. Its official designation is thus 1I/2017 U1, with the “I” standing for “interstellar”—the first time this designation has ever been used.
That is exciting. Some scientists, though, entertain an even more exciting possibility: what if ’Oumuamua is not an asteroid, as most think, but an alien spacecraft? Asteroids come in all sorts of shapes and sizes, but ’Oumuamua seems particularly odd. As best as astronomers can tell, it is cigarlike, being roughly 180 metres long but only about 30 metres wide. That makes it more elongated than anything known of in the solar system. Such a shape would be a sensible choice for a spaceship, since it would minimise the scouring effect of interstellar dust.