What is unique about the interstellar object 'Oumuamua'?

• A. It is the first object of its kind observed in our solar system.
• B. It is the largest asteroid discovered.
• C. It originates from the Andromeda galaxy.
• D. It was visible to the naked eye from Earth for months.

Answer: (A)

An object from outside the solar system passing through ours was detected for the first time. Oumuamua’s motion followed a hyperbolic path and its speed couldn’t be explained by something bound to the Sun, which reveals that it came from beyond our solar system. That combination—first-ever observed interstellar visitor and a trajectory indicating an extrasolar origin—is what makes it unique.

It isn’t the largest asteroid; estimates of its size are modest and its shape appeared elongated, not characteristic of the largest known asteroids. It certainly didn’t originate from another galaxy like Andromeda, since it merely traveled through our region of the Milky Way. And it wasn’t visible to the naked eye for months; it was far too faint and was detected only with telescopes for a relatively brief period.