What is "sub-brown dwarf"

n. A planetary mass object, less massive than a brown dwarf star, and not in orbit around a star.

thumb|upright=1.2|Comparison: the Sun, a young sub-brown dwarf and Jupiter. As the sub-brown dwarf ages, it will gradually cool and shrink.

A sub-brown dwarf or planetary-mass brown dwarf is an astronomical object that formed in the same manner as stars and brown dwarfs (i.e. through the collapse of a gas cloud) but that has a mass below the limiting mass for thermonuclear fusion of deuterium (about ). Some researchers call them free-floating planets whereas others call them planetary-mass brown dwarfs.