Johannes Kepler flatly rejected the idea of planets orbiting other stars, so there is a certain irony in NASA naming a $600 million telescope after him in 2009 to prove him wrong. This deep dive explains how the Kepler Space Telescope used the transit method to watch roughly 150,000 stars for brightness dips of about 0.01 percent, why it needed a 1.4-meter ultra-low expansion mirror and a 94.6-megapixel array of 42 CCDs, and why its software threw away 94 percent of image data to fit through 1970s-era deep space bandwidth limits. It also explains why the spacecraft was placed in an Earth-trailing heliocentric orbit, drifting 16 million miles farther away each year.

The story turns when stellar noise proved stars were twice as variable as expected, forcing a mission extension just as the reaction wheels began to fail in 2012 and 2013, their  ...