Planet
The smallest known planet is PSR B1257+12A, one of the first extrasolar planets discovered, which was found in 1992 in orbit around a pulsar. Its mass is roughly half that of the planet Mercury. The smallest known planet orbiting a main-sequence star other than the Sun is Kepler-37b, with a mass (and radius) slightly higher than that of the Moon.
Kepler-47
The binary system is known to host three planets, all larger than Earth with no solid surface. The innermost planet, Kepler-47b, is a gas giant and resides close to its parent stars and therefore is inhospitable to life. It is thought to be smaller than Kepler-47c and is roughly three times the radius of Earth. The second planet, Kepler-47c, is also a gas giant and the outermost planet. It is situated within the habitable zone and its radius is 4 times the Earth's. Although it is assumed Kepler-47c is not capable of harboring life, it is marginally larger than Neptune and could possibly have a dense atmosphere of water vapor. The latest exoplanet to be discovered in the system was Kepler-47d, announced as being discovered in November 2013. This planet is about the size of planet "c", but orbits farther in then c does. It completes an orbit every 187.3 days.