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.
List of possible dwarf planets
After Brown and Tancredi made their calculations, it was discovered that Iapetus (1,470 km in diameter) and the smaller moons of Saturn down to Mimas with well-determined shapes are not in hydrostatic equilibrium as had been thought. They have a hydrostatic shape that froze in some time ago and that does not match the shape an equilibrium body would have at their current rotation rates. Ceres, at 950 km, is the smallest body for which detailed measurements are consistent with hydrostatic equilibrium. It is not clear whether trans-Neptunian objects would behave more like Ceres or Iapetus; thus, some or all trans-Neptunian dwarf planets smaller than Pluto and Eris might not actually be in equilibrium. The IAU has not addressed the issue since these findings.