KOI-314c, shown in this artist's conception, is the lightest planet to have both its mass and physical size measured. Surprisingly, although the planet weighs the same as Earth, it is 60 percent larger in diameter, meaning that it must have a very thick, gaseous atmosphere. It orbits a dim, red dwarf star (shown at left) about 200 light-years from Earth. KOI-314c interacts gravitationally with another planet, KOI-314b (shown in the background), causing transit timing variations that allow astronomers to measure the masses of both worlds. This serendipitous discovery resulted from analysis as part of the Hunt for Exomoons with Kepler (HEK) project.