People have long wondered about the existence of worlds outside of our solar system. Since 1995, significant progress has been made in the search for extrasolar planets, with over 155 planets found. But the questions remain whether there are other planets similar to Earth and whether humans are alone in the universe. This video from NASA, created in September 2004, outlines the plans for future missions and the search for Earth-like worlds.
This media asset comes from PlanetQuest by NASA.