In the mid-1990s, astronomers made history when they detected three planets orbiting stars in the Milky Way. The planets were nothing like Earth, however: They were giant gas balls like Jupiter or Saturn. More than 500 planets have been found since then, yet none of them could support life. Now, armed with more powerful technology, planet hunters are racing to find a true twin of Earth. Science writer Michael Lemonick has unique access to these exoplaneteers, as they call themselves, and Mirror Earth unveils their passionate quest. Geoff Marcy, at the University of California, Berkeley, is the world's most successful planet hunter, having found two of the first three extra-solar planets. Bill Borucki, at the NASA Ames Research Center, struggled for more than a decade to launch the Kepler mission - the only planet finder, human or machine, to beat Marcy's record. David Charbonneau, at Harvard, realized that Earths would be much easier to find if he looked at tiny stars called M-dwarfs rather than stars like the Sun - and that he could use backyard telescopes to find them! Unlike those in other races, the competing scientists actually consult and cooperate with one another. But only one will be the first to find Earth's twin. Mirror Earth is poised narrate this historic event as the discovery is made.