The “interstellar asteroid” is not an asteroid after all. A detailed study of its path as it hurtled through our solar system indicates that it might actually be a comet, made mostly of ice instead of solid rock.

In October 2017, astronomers spotted an object, later named ‘Oumuamua, flying through our solar system at an unusual angle. Analyses of its trajectory showed that it wasn’t circling our sun, but rather simply passing through. It was the first-ever seen interloper from another star, hurled in our direction from somewhere in the …