The first rocky planet discovered by NASA’s Kepler mission was Kepler-10b.
Kepler-10b was announced on January 10, 2011, after NASA’s Kepler spacecraft observed repeated transits—tiny dips in its host star’s brightness. Follow-up measurements from the Keck Observatory detected the star’s radial-velocity wobble, confirming the planet and helping determine its mass.
The planet is about 1.47 times Earth’s radius and roughly 3.7 times Earth’s mass. It circles Kepler-10 in only 0.84 Earth days at an extremely close distance, so its dayside temperature is hot enough for molten rock. It is rocky, but emphatically not Earth-like in climate or habitability.
Kepler-10b is sometimes confused with later headline-making worlds such as Kepler-186f and Kepler-452b. Those planets became famous for their Earth-sized or habitable-zone characteristics, whereas Kepler-10b’s historical importance is that it was Kepler’s first confirmed terrestrial planet. The earlier CoRoT-7b is often discussed in comparisons, but its composition was less certain.