Theoretical physicist Prof. Stephen Hawking and science philanthropist Yuri Milner unveiled this week a new initiative, called Breakthrough Starshot, to send light-propelled nanocrafts toward Alpha Centauri. This artist’s impression shows Alpha Centauri Bb orbiting the star Alpha Centauri B, a member of the triple star system that is the closest to Earth. Alpha Centauri B is the most brilliant object in the sky and the other dazzling object is Alpha...