Researchers weren't surprised that Oumuamua and the recently discovered interstellar comet 2l/Borisov (discovered only a few weeks ago) reached our solar system. In fact, they expect this to be the start of a very long list of interstellar guests.
On October 19th, 2017, the Panoramic Survey Telescope and Rapid Response System-1 (Pan-STARRS-1) in Hawaii announced the first-ever detection of an interstellar asteroid, named 1I/2017 U1 (aka. ‘Oumuamua). Originally thought to be a comet, this interstellar visitor quickly became the focus of follow-up studies that sought to determine its origin, structure, composition, and rule out the possibility that it was an alien spacecraft!
This month, scientists were able to confirm for the first time that a visitor from another part of the galaxy has entered our neck of the celestial woods. This strange space rock, initially thought to be a comet, is the first interstellar object we have ever been able to observe within our solar system.