25 percent of stars have a so-called "super-Earth" (worlds 1.25 to 2 times as big as our own)
Only 5 percent of stars harbor a gas giant with an orbital period of 400 days or less, researchers said.
Kepler detects alien worlds by noting the telltale dips in brightness caused when planets cross the face of — or transit — their parent stars from the instrument's perspective.
minimum of 17 billion small, rocky alien worlds, or an Earth-size planet around one of every six stars.