Before this date, all known exoplanets had been discovered by indirect methods, via transits and radial velocities, while this image shows the first exoplanet photographed directly!
2M1207b, that is its name, is orbiting a brown dwarf located 250 light-years from Earth, in the constellation of Hydra. Among the many records held between this planet is also that of being the first planetary mass object to be discovered around a brown dwarf.
The planet is a gas giant located on an orbit with a semi-major axis of 55 AU. Its physical parameters are not yet known, but it is believed to have a mass of less than 10 Jovian masses.
This would seem to confirm that 2M1207b is indeed a planet, since its mass is less than that deemed necessary for the fusion of deuterium to take place in its nucleus (about 13 Jovian masses)in which case it would be classified as a brown dwarf.
The brown dwarf - system of exoplanets was found in the infrared. In these wavelengths the planet still shines with the residual heat of its formation and is therefore easier to photograph than in the visible.
No wonder the first planet photographed directly was observed orbiting a brown dwarf. A normal star is in fact much brighter than a brown dwarf: thinking of a system composed of a star and a planet, the light of the latter would be lost in the halo of the star, making it very difficult to observe.
The last aspect that facilitated the discovery of 2M1207b was its large angular separation from the brown dwarf. If it had been on a more internal orbit, the planet would have been lost inside the glowing halo of the brown dwarf.
Credit: ESO.-
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