Back in October 19th, 2017, a celestial object has been discovered by the University of Hawaii's Pan-STARRS1 telescope. It's name is 1I/2017 U1, nicknamed as Oumuamua. Even though it has been initially classified as "Comet" but later on it has been identified as an "Asteroid". The reason behind that was, this object did not reveal any comet like activity (spewing gases/comet tail) while slingshotted past our sun on September 9, 2017.
It is being assumed that for the very first time, human kind has discovered an interstellar object that is most probably came from another star or outer solar system. The logic behind such claim is fairly strong as such unusual shaped (elongated) asteroid has never been discovered in the past. It has been estimated to be 800 feet in length and 100 feet in width. Also the aspect ratio of this object (10:1) is far higher than any other asteroid (typically 3:1) that has been discovered within our solar system to date.Illustration of Interstellar Asteroid 1I/2017 U1 (Oumuamua).
Perhaps the most intriguing part was it's speed. It entered into our solar system at a speed that no other object within our solar system does. However, it gained even more speed and reached up to 196,000 miles per hour (87.3 kilometers per second) as it neared the Sun. At such speed even Sun's gravity could not hold this asteroid under it's own system (like rest of the planets). Slowly but surely it lost some of its speed as it was moving further away from the Sun towards unknown destination.
This asteroid was also very reddish in color which helped scientists at Nasa Jet Propulsion Lab to conclude that this steroid has definitely came from outer space. An asteroid may turn into such color due to the high effect of cosmic ray for over millions of years.
It is very important to understand that the asteroid belt of our solar system holds a large number of asteroids. However, these asteroids are fairly small (except 4 Vesta, 2 Pallas, and 10 Hygiea) in size and can not gain speed like Oumuamua. Even though not discovered yet the theoretical Oort Cloud is known to be the home for large number of icy materials (presumably comets) and very few asteroids.