3. Alpha Centuri
The closets star system to our sun, this system consists two main stars- Alpha Centauri A and Alpha Centauri B, along with Proxima Centuari which is a slightly smaller star. Between these stars is Alpha Centauri Bb, which is the closets extrasolar planet to Earth ever discovered. It is also, however, supposedly far too hot to maintain life. But with a system such as this, the existence of another planet, slightly further from Alpha Cenauri A, is definitely possible and would be a great place for an alien race to hide their base camp while they abduct people from the Bermuda Triangle! Okay, maybe the Bermuda Triangle and Alpha Centauri wouldn't be related in an episode but the idea of The Doctor coming across a planet (relatively) close to Earth that could be inhabited by humanoid creatures and who seek to invade our planet because theirs is becoming too hot would make for another fantastic episode. I mean, during the original Lost In Space TV show all they wanted was to get to Alpha Cenauri! There's gotta be life there by now....