Philip Lucas of the University of Hertfordshire and Patrick Roche of the University of Oxford spotted the objects in the Orion Nebula last year, but their characterization of them as planets was disputed by other scientists who argued that they might be normal stars far more distant than the Orion Nebula that simply looked like young planets. In their new study, Lucas and Roche measured the spectrum of infrared light emissions of the 20 objects and found the characteristic signature of water vapor. Because an atmosphere containing water vapor can only exist around an object far colder than a star, the team concluded that the objects are young, low-mass bodies and that the faintest of them are of planetary mass. "It's exciting to find these planet-sized objects floating around space, unlike planets such as our Earth, which orbits a star," Lucas says. "Our new results provide the first step in the exploration of their physical properties."
The only reason why these objects can be seen at all is that they are still quite warm from the formation process, thus permitting detection of their infrared light emissions. "The identification and study of these objects is extremely interesting in itself," Roche says. "But it can also aid our understanding of the star formation process, which is one of the major mysteries in astronomy."
The discovery also adds fuel to the controversy surrounding the definition of what constitutes a planet¿a debate that originated with a dispute over the status of Pluto. The possibility exists that these planets formed in the same way stars form, which has led some scientists to argue that they shouldn¿t be called stars. The authors suggest "planetars" as a compromise.