Gas giant
The smallest known extrasolar planet that is likely a "gas planet" is Kepler-138d, which has the same mass as Earth but is 60% larger and therefore has a density that indicates a thick gas envelope.
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.