Sub-brown dwarf

From Vinidia

A sub-brown dwarf or planetary-mass brown dwarf is a celestial 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 13 M_J).

Lower mass limit

The smallest mass of gas cloud that could collapse to form a sub-brown dwarf is about 1 Jupiter mass (M_J). This is because to collapse by gravitational contraction requires radiating away energy as heat and this is limited by the opacity of the gas. A 3 M_J candidate is described in the paper.