When astronomers first spied a weird cigar-shaped object speeding past the sun last October, they could tell from its path that it had come from another star system — but they didn't know exactly what it was.
Now they know. A study published Wednesday in the journal Nature indicates that the interstellar visitor, dubbed Oumuamua, is neither an asteroid nor an alien spacecraft (as some wags had suggested) but a small interstellar comet, NBC News MACH reported.
Comets — icy, dusty objects that have been likened to "dirty snowballs" — typically form long tails when they come close to the sun. No such tail was visible in earlier observations of Oumuamua (which means "scout" in Hawaiian), a fact that helped lead other astronomers to conclude that it was an asteroid.
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But an analysis of new observations made by ground-based telescopes and the Hubble Space Telescope yielded a surprise: Oumuamua's trajectory couldn't be explained solely by the gravitational forces exerted on it by the sun and the planets — as would be the case if it were an asteroid, or space rock.