Astronomers have found the first interstellar object in the solar system, named 1I/2017 U1 (`Oumuamua):
A few weeks ago, we reported on a small object visiting from beyond our solar system. Now astronomers have scrutinized data from this object, which has been given the name `Oumuamua, and which must have traveled through space for millions of years before its chance encounter with our star system. The conclusion is that it’s a dark, reddish, highly-elongated rocky or high-metal-content object. And, indeed, it is the first known asteroid from interstellar space. These new results were published today (November 20, 2017) in the peer-reviewed journal Nature.
Some astronomers thought the object was a comet when the Pan-STARRS 1 telescope in Hawai`i first picked it up on October 19, as a faint point of light moving across the sky. Others thought it looked like a typical fast-moving small asteroid. As they tracked its motion through space, astronomers began to be able to calculate its orbit, showing beyond any doubt that this body did not originate from inside our solar system, like all other asteroids or comets ever observed.
Instead, this object was doubtless from interstellar space.
Bottom line: Astronomers report on the first known interstellar asteroid, which swept nearest our sun in September, then sped away again. Astronomers have named this object `Oumuamua and say it is dark red and very elongated.
For some reason, the Arthur C. Clarke novel Rendezvous with Rama comes to mind.