How to Build the Machine That Will Find Another Living Earth

The 20-year stretch since the discovery of the first exoplanet--a planet circling a star other than the sun--has seen a wholesale relocation of cool ideas from science fiction over to science fact. By 1999, scientists found a way to study the composition of exoplanets. By 2004, they identified a rocky planet, broadly similar to Earth in structure. By 2014, they tracked down an Earth-size world that is the right distance from its star for liquid water. The Star Trek vision of a galaxy full of h