Transit light curves of Kepler-139c from Kepler (black) along with the best-fit models (red). Fits were performed using the short-cadence (1 minute) light curves when available, but the data are shown here in 30 minute bins for ease of visualization. The gray dashed line marks the expected transit midpoint if the planet’s period were exactly constant. The data reveal TTVs of up to ∼0.5 hr.