The closest star system with planets might well be the Tau Ceti solar system, less than 20 light years from the earth. There’s a lot of excitement about Tau Ceti, as we add space telescopes to our astronomical research capabilities, some scientists think they have discovered a planet in the inhabitable zone of the solar system. In short, a planet orbiting a star needs to receive the solar radiation to maintain a temperature where water is liquid, not always ice or steam. More on the Tau Ceti here.