have been proposed. Alternatively, 2M1207b might be dimmed by a surrounding disk of dust and gas. 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. Although the mass of 2M1207b is less than that required for deuterium fusion to occur, some 13 times the mass of Jupiter, and the image of 2M1207b has been widely hailed as the first direct image of an exoplanet, it may be questioned whether 2M1207b is actually a planet. Some definitions of the term planet require a planet to have formed in the same way as the planets in the Solar System did, by secondary accretion in a protoplanetary disk. With such a definition, if 2M1207b formed by direct gravitational collapse of a gaseous nebula, it would be a sub-brown dwarf rather than a planet. A similar debate exists regarding the identity of GQ Lupi b, also first imaged in 2004. 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. As of 2006, the International Astronomical Union Working Group on Extrasolar Planets described 2M1207b as a "possible planetary-mass companion to a brown dwarf." See also Extrasolar moon HD 172555 Rogue planet References External links ESO Press Release 12/05:Yes, it is the Image of an Exoplanet BBC: Planet 'seen' around distant sun Space.com - Astronomers Confident: Planet Beyond Solar System Has Been Photographed Space.com article on the discovery "A Giant Planet Candidate Near a Young Brown Dwarf" (PDF) from the European Southern Observatory. Space.com: Fresh Debate over First Photo of Extrasolar Planet "A Moving Cluster Distance to the Exoplanet 2M1207 B in the TW Hydrae Association" "The Planetary Mass Companion 2MASS 1207-3932B: Temperature, Mass, and Evidence for an Edge-on Disk" "Planet collision could explain alien world's heat" 2M1207 Centaurus (constellation) TW Hydrae association Giant planets Exoplanets discovered in 2004 Exoplanets detected by direct imaging