Extrasolar planet Lists of extrasolar planets
Observed position
Observed separation (d) 41 ± 5 AU
Physical characteristics
Mass (m) 3.3+1.5-1.0 MJ
Radius (r) 1.5 RJ
Density (ρ)  ? kg/m3
Temperature (T) 1250 ± 200 K
Discovery information
Discovery date 2004
Discoverer(s) Chauvin et al.
Detection method Imaged
Discovery status Confirmed

2M1207b is an extrasolar planet orbiting the brown dwarf 2M1207, a star in the constellation Hydra approximately 200 light years from Earth. Notable as one of the first extrasolar planets to be directly observed (by infrared imaging), it was discovered in early 2005 by the Very Large Telescope at the Paranal Observatory in Chile by a team from European Southern Observatory led by Gael Chauvin. It is believed to be about five times the mass of Jupiter and orbits its sun at a distance nearly twice as far as Neptune is from the Earth's Sun.

Provisionally named 2M1207b, the gas giant planet is, like its primary, very hot; the estimated surface temperature is roughly 1250 K (976°C or 1790°Fahrenheit). The planet's mass is about five times that of Jupiter, well below the calculated limit for deuterium fusion in brown dwarves, which is 10-13 Jupiter masses. The projected distance between 2M1207b and its primary is around 41 AU (similar to the mean distance between Pluto and the Sun), giving it an estimated orbital period of around 1700 years. The infrared spectrum of the planet indicates the presence of water molecules in its atmosphere. The planet is not a likely candidate to support life, neither on its surface nor on any satellites.

Discovery and identification

2M1207b is about 100 times fainter in the sky than its companion star, and was first spotted as a "faint reddish speck of light" in 2004, and was inconclusively imaged by the Hubble Space Telescope later that year. Images taken in February and March 2004 by the Very Large Telescope array were more conclusive, and suggest a mass of about 5 Jupiters, although other methods suggest a slightly smaller mass. As with any astronomical object, adjacency in the sky does not necessarily mean that two objects are gravitationally bound (see optical binary); however, observations over time show with high confidence that the two objects (2M1207 and 2M1207b) show similar proper motion in the sky and are therefore part of the same stellar system.


Closer View of 2M1207b

Although widely hailed as the first direct image of an extrasolar planet (due to the fact that it's mass is less than that required for Deuterium fusion to occur, some 14 times the mass of Jupiter), some question whether 2M1207b is actually a planet. Some astronomers doubt that the body formed in the same way as the planets in our solar system (formation in a planetary disk). Such objectors say the body likely formed in the same way stars are formed, from gravitational collapse of a gaseous nebula. If this interpretation is correct, the object would not be a planet, but would be another brown dwarf, and the system would then be a binary system consisting of two brown dwarfs. A similar debate exists regarding the identity of GQ Lupi b, also first imaged in early 2005. On the other hand, the discovery of marginal cases like Cha 110913-773444--a free-floating, roughly planetary-mass brown dwarf, raise the question of whether distinction by formation is a reliable dividing line between "stars/brown dwarfs" and "planets."

As of May 2005, the International Astronomical Union officially described 2M1207b as "a possible planetary-mass companion to a brown dwarf."

In December 2005, American astronomer Eric Mamajek reported a more accurate distance estimate to the 2M1207 system of 53 parsecs (173 light years) by calculating a moving-cluster parallax. The revised distance means the luminosities and inferred masses of the 2M1207 system were decreased, from an original estimated mass and separation of 5 Jupiter masses and 55 AU respectively.

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