There are two major sources of comets in our Solar System: the Kuiper Belt (pronounced KI-per) and the Oort Cloud. Comets from both sources wend their way into the inner Solar System, but interactions with Jupiter and the other giant planets can launch them out of the Solar System, never to return. Similarly, Jupiter-like planets around other stars can also eject extra-solar comets into interstellar space. Astronomers have not confirmed the existence of any extra-solar comets yet, but because the distances between stars is so large, encounters with our Solar System are expected to be very rare. Models predict that extra-solar comets should wander into our Solar System only once every few centuries or so. An extra-solar comet would be very easy to identify, arriving with a speed far above that of Kuiper Belt or Oort cloud comets. For more on interstellar comets click here.