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.
Brown dwarf
The brown dwarf Cha 110913-773444, located 500 light years away in the constellation Chamaeleon, may be in the process of forming a miniature planetary system. Astronomers from Pennsylvania State University have detected what they believe to be a disk of gas and dust similar to the one hypothesized to have formed the Solar System. Cha 110913-773444 is the smallest brown dwarf found to date (), and if it formed a planetary system, it would be the smallest known object to have one. Their findings were published in the December 10, 2005 issue of Astrophysical Journal Letters.