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 directly imaged exoplanets
The data given for each planet is taken from the latest published paper on the planet to have that data. In many cases it is not possible to have an exact value, and an estimated range is instead provided. The least massive planet is Fomalhaut b, which has a mass of 2 M or less. The coldest and oldest is 59 Virginis b with a mean temperature of 240 °C and age of 100–500 million years.
This list includes the four members of the multi-planet system that orbit HR 8799.