Our sun is surrounded by a cloud of comets. In the past, there probably were a lot more of them, the debris left over after the formation of the solar system. Presumably, other stars also have their own cometary companions. But it is difficult for any comet to escape from the gravity well of its parent star; it would require an interaction in it’s own system with a another body which could give it the additional gravitational boost needed to exceed stellar escape velocity.

Comets approaching the sun on hyperbolic orbits will never be captured by Sol unless some third body interacts with them, absorbing excess kinetic energy. So all the comets we have seen so far have either elliptical orbits, or parabolic ones (the parabola does not circle back on itself, it is the intermediate curve between ellipse and hyperbola, but it is extremely difficult to tell a parabola from an extremely skinny ellipse). We have detected several comets with apparently parabolic orbits, but they could be members of our own solar system.

This object is apparently in a true hyperbolic orbit, it must be an outsider, which according to the article is corroborated by other considerations. It is an interstellar visitor. I find this absolutely stunning.

http://www.skyandtelescope.com/astronomy-news/astronomers-spot-first-known-interstellar-comet/?utm_source=newsletter&utm_campaign=sky-jma-nl-171027&utm_content=978262_EDT_SKY_171027&utm_medium=email