2M1207b is a planetary-mass object orbiting the brown dwarf 2M1207, in the constellation Centaurus, approximately 170 light-years from Earth.

[6] It is believed to be from 5 to 6 times the mass of Jupiter[3] and may orbit 2M1207 at a distance roughly as far from the brown dwarf as Pluto is from the Sun.

[7] The object is a very hot gas giant; the estimated surface temperature is roughly 1200 K (930 °C or 1700 °F),[3] mostly due to gravitational contraction.

[5] In December 2005, American astronomer Eric Mamajek reported a more accurate distance (53±6 parsecs) to 2M1207b using the moving-cluster method.

[8] As an unlikely possibility, Mamajek and Michael Meyer have suggested that the planet is actually much smaller, but is radiating away heat generated by a recent collision.

[16][17] The mass ratio of 2M1207b and 2M1207 is approximately 0.22, which exceeds the L4/L5 instability threshold and therefore means 2M1207b does not qualify as an exoplanet under the IAU's definition.

[19] On the other hand, the discovery of marginal cases like Cha 110913-773444—a free-floating, planetary-mass object—raises the question of whether distinction by formation is a reliable dividing line between stars/brown dwarfs and planets.