An interstellar object is a body other than a star or substar located in interstellar space, and not gravitationally bound to a star.
Recently an interstellar object believed to be from another solar system was seen in ours. Our Solar System’s recent interstellar visitor a space rock named `Oumuamua may be covered in a thick coat of organic material, an outer layer that’s protecting a cache of ice within. This veneer may have acted like a shield, preventing the ice inside `Oumuamua from getting overheated and evaporating when the rock passed close by our Sun. That means this interstellar object may be more like an icy comet and less like an asteroid.
The main distinction between asteroids and comets is their composition: comets are made up of a mixture of ice and rocks, whereas asteroids are mostly rock and metal, without much water. Astronomers think that most of the objects passing in between stars called interstellar space are more comet - like than asteroid - like.
Oumuamua has caused quite a buzz in the astronomy, planetary - science and SETI communities since the asteroid was detected in mid - October. The object's trajectory reveals that it came here from another solar system, and its weird, extremely elongated shape has sparked speculation that the rock could be an alien spacecraft of some sort.